DNA Detectives

DNA: it's the genetic information that makes plants and animals what we are. Most of the time when you hear about it in the context of food, it's to do with breeding. But in this short episode, we bring you two DNA detective stories that show how genetic analysis can rewrite the history of agriculture and fight food fraud—at least some of the time.

Listen now to hear how preserved DNA from an underwater site off the coast of Britain is helping paint a picture of how hunter gatherers in Northern Europe might first have experienced the wonders of agriculture, by trading kernels of exotic, domesticated Near Eastern wheat over long distances. We'll also explore DNA's role in some controversial accusations of food fraud and introduce you to the mysterious publication that defines the official standards of identity for food ingredients. And, finally, we squeeze in a short trip to Dublin's Science Gallery, to talk to chef Clare Anne O'Keefe about a dish that was entirely inspired by Gastropod!


TRANSCRIPT Are Insect Guts the Secret to the Most Delicious Kimchi?

This is a transcript of the Gastropod episode, Are Insect Guts the Secret to the Most Delicious Kimchi?, first released on December 3. It is provided as a courtesy and may contain errors.

CYNTHIA GRABER: You recording? Yep, OK. So now I am going to massage my cabbage. SOUNDS. Okay, number two, well massaged cabbage. Now for a large bowl for cabbage number three.

GRABER: Just what I like to do on a Saturday afternoon in the fall, give some cabbage a very deep massage.

TWILLEY: I prefer to be the one actually getting a massage myself. But you are not alone Cynthia: this is an autumn ritual for millions of people. Primarily Koreans.

GRABER: Because fall is the traditional time to make kimchi, and that’s what I was doing, and that’s what this episode is about.

TWILLEY: You’re listening to Gastropod, the podcast that looks at food through lens of science and history. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber. And I wasn’t just making kimchi for fun—and, yes, deliciousness. I was making it for science. What’s going on in the fermentation, and where do the microbes that transform cabbage and other veggies into kimchi come from?

TWILLEY: These are good questions. But while we wait for your microbes to get busy and then get sequenced, I have other kimchi questions. Like what’s the difference between kimchi and sauerkraut—aren’t they both fermented cabbage?

GRABER: Plus, is kimchi actually Korean—and what’s it doing in tacos today? How and when did it get so trendy? And has that changed kimchi in the process?

TWILLEY: We’ve got all that plus so many microbes that you are all going to fall down drunk.

GRABER: This episode is supported in part by the Alfred P. Sloan Foundation Program for the Public Understanding of Science, Technology, and Economics.


KEVIN KIM: So kimchi is a lot of different things to a lot of different people.

TWILLEY: This is Kevin Kim. He is a food ethnographer and PhD candidate at the University of Maryland. And Gastropod listener Calvin Ho recommended that we give Kevin a call to talk about, yes, kimchi.

KIM: Basically it is a traditional Korean dish of fermented vegetables, the formula of which is normally fermented seasonal vegetables with some form of fermented seafood. Sometimes in the form of anchovies, brined shrimp, but it runs the gamut.

GRABER: In the US, the kind of kimchi we nearly always eat is made of cabbage. But Lauryn Chun—she owns a kimchi company called Mother-in-Law’s and she wrote The Kimchi Cookbook—she says it doesn’t have to be.

CHUN: It can be made with any vegetables really. so it’s not necessarily a Napa cabbage that makes it kimchi. It’s the process of fermenting and pickling.

TWILLEY: That process— the fermentation—it produces a, shall we say, distinctive smell.

KIM: It’s hard to describe having grown up with it my whole life. But I would say you know to me it just smells like home. But I think it’s a vegetal funk that you might get from something like sauerkraut, interspersed with the sort of sharp aromas of onion and garlic and scallions.

GRABER: And actually, sauerkraut and kimchi are both made through the same fermentation process. There are two main differences—one is the type of cabbage, sauerkraut is usually made with that hard greenish round cabbage and not frilly Napa cabbage. The other one is the differences in the seasonings. But the fermentation method, that’s the same.

KIM: And for the most part kimchi is flavored with red pepper. So sometimes it’s quite spicy but it doesn’t necessarily have to be. There are varieties that are not spiced. But that fermentation, that lactic acid bacteria is what gives it its zip and zing. That’s what gives it what Koreans call life.

GRABER: There’s an old saying in Korea that kimchi is half of all the food provisions.

KIM: Koreans traditionally have kimchi at all three meals. Breakfast, lunch, and dinner. It’s served as a side. It’s sort of omnipresent on the side. You know, a lot of people will say without kimchi there’s no—there is no meal. I was born in South Korea but I immigrated to the United States when I was two. But even when I was in L.A.—we first moved to L.A.—kimchi was always on the on the table. We always had jars of it.

TWILLEY: So, if you’re Korean, you’re likely never far from kimchi when you’re at home. But sometimes Koreans need to travel to places where kimchi might not be on every table.

KIM: Because they want to have kimchi with almost every meal, they’ll pack kimchi. And sometimes the jars, because of the pressurization and the the fact that kimchi is alive with lactic acid bacteria, will sometimes explode mid-flight.

TWILLEY: The chefs at one of LA’s trendiest restaurants, Animal, actually had this happen to them—they’d cryovaced some kimchi to bring it along with them, and when they got to the baggage carousel, it was complete carnage. Everyone was gagging and holding their shirts over their noses.

GRABER: Kevin says there are entire Korean blog posts devoted to making sure your kimchi won’t explode on the plane and overwhelm your fellow passengers for the next however many hours.

TWILLEY: When Lauryn and Kevin were growing up in the US they ate tons of kimchi, of course, but that pungent vegetal funk—it was a problem, at least around non Korean Americans.

CHUN: The one thing that—admonition that my mom always told me was to never eat kimchi with with anyone who wasn’t Korean.

KIM: Early on I remember having it in my lunches. And of course being made fun of for it because, you know, of that vegetal funk. And having some semblance of perhaps embarrassment or shame. You know, I would ask my mom why can’t you just pack me peanut butter and jelly sandwiches

GRABER: Of course that’s all changed now. Kevin is proud of kimchi.

TWILLEY: But my question is how does cabbage, which, you know, I like cabbage OK, but it’s just cabbage—how does that become this essential source of zip and zing?

GRABER: Basically, there’s one bacteria called lactobacillus—you listeners might remember it from our sourdough episode, because, along with yeast, it’s a key part of sourdough starters.

TWILLEY: These lactobacillus, they’re also called lactic acid bacteria. And they live to eat the sugars in the cabbage leaves. And then they excrete. They excrete acid, which is sour, and they fart out carbon dioxide—that’s the bubbles and more of the sourness.

GRABER: So these lactic acid bacteria are the key to kimchi. And whenever we at Gastropod want to get up close and personal with the microbes in our foods, we know who to call.

WOLFE: I’m Ben Wolfe and I am an assistant professor at Tufts University. And Gastropod’s in-house microbiologist.

GRABER: Not only is he our very own in-house microbiologist—

TWILLEY: Not every podcast has that but we are special—

GRABER: So true. But as it happens, Ben is also in the middle of a huge kimchi research project! Perfect.

WOLFE: So there was a sort of baseline understanding of the traditional types of lactic acid bacteria that you would find in your average kimchi. And most of this work was in Korea. And so most of it was looking at what are the types of bacteria. And also looking at this very clear succession, this temporal change of microbes from the beginning of when you first put that kimchi in a jar and close it up, to the whole fermentation process all the way to the end.

TWILLEY: So if Korean scientists have figured all that out already, what’s left for Ben to study?

WOLFE: So one thing that I find really fascinating about kimchi compared to other fermented foods is that unlike cheese or yogurt where you use starter cultures, these microbes that you buy, kimchi and sauerkraut and other fermented vegetables are not inoculated.

GRABER: When you make sauerkraut or pickles or kimchi, you don’t ever use a starter culture. The microbes just kind of get in there.

TWILLEY: So, unsurprisingly, people like Ben are curious about where these microbes come from. And they’ve tested various possible sources. Like maybe it’s us? We’re the source?

WOLFE: So this is an interesting idea. The kimchi hands or the idea that humans can be an inoculum source for fermented foods. In fact, there was really cool study recently here in Massachusetts looking at a sauerkraut production facility, similar to kimchi, and they sampled lots of different things in the environment—the workers, the walls. And then they also sampled the raw materials, the cabbage. And they found the cabbage was really the primary source for these bacteria.

GRABER: Ben thinks this is actually pretty surprising and amazing: that we can just go out, pick or buy all sorts of vegetables grown nearly anywhere in the world, and we can basically always find these beneficial lactic acid bacteria.

WOLFE: And so I started to think, well, where are they coming from? What’s the origin story for these lactic acid bacteria? How did they get to the plant? Do different farms have different types or different abundances of lactic acid bacteria?

TWILLEY: So Ben and his graduate student Esther Miller set out to answer these questions.

WOLFE: She and others in the lab, we all went out and surveyed farms throughout New England. And so we went to New Hampshire, throughout Massachusetts, Connecticut, a little bit into the Hudson Valley as well, and said: Where are these lactic acid bacteria? What are they in terms of the species and how abundant are they in the environment? And we went to these 51 farms—some of them are community gardens, most of them are really small farms. And we sampled the soil. And then we also sampled the leaves of weeds and other plants in the environment. We didn’t directly sample cabbage. We just wanted to say: What is the potential source of these bacteria? Because they have to hide out somewhere when they’re not growing on the cabbage leaf.

GRABER: And they did find lactobacillus, but not as much as they expected.

WOLFE: They’re incredibly rare in the environment. So it’s actually really hard to find them. So if you look in soil or if you look on leaves they’re usually less than 1 percent of all the types of bacteria that are in the environment. And to us that was kind of surprising because it really does suggest that we’re relying on these rare and somewhat variable groups of microbes to do this important fermentation process.

TWILLEY: One of the reasons Ben and Esther think that these lactic acid bacteria are so rare on farms is because they aren’t particularly comfortable there. It’s just not their happy place.

WOLFE: They’re really good at fermenting sugars in a low oxygen, somewhat salty and cold environment. So if you think of your average cabbage leaf hanging out in a farm field in August, it’s none of those things.

GRABER: Ben and Esther wanted to make sure that these lactic acid bacteria truly didn’t love farm fresh cabbage leaves. So they grew tiny sterile cabbages in the lab—cabbages with literally no microbial life.

WOLFE: So what you do is you take cabbage seeds and you sterilize the surface of the cabbage seeds with ethanol and a little bit of bleach. And then you put them in this sterile clay medium that we have inside of a test tube. And you grow them—they happily grow in these test tubes. The Napa cabbages love this environment. And then what we can do is spray those plants with different combinations of microbes.

TWILLEY: And basically the lactic acid bacteria all die.

WOLFE: So it’s not even that they’re bad at getting to the plant but, once they do, they slowly just decrease in abundance. So they’re not even really good at fighting in that leaf environment where there’s lots of other bacteria that will happily grow. So again it’s sort of a magical thing that kimchi and sauerkraut even works because we’re relying on this really rare group of microbes.

GRABER: Okay, they are rare, but, like we said earlier, there are a whole bunch of different kinds of lactic acid bacteria that you can find in a kimchi fermentation. So do those different varieties make a difference to your final kimchi?

WOLFE: One of the questions that we’re interested in is, what species you start off with in terms of the cabbage you’re bringing in from the farm—how does that control or contribute to the fermentation process and ultimately the flavor and quality of the product? Because you would get different microbes growing on different plants. And so we’re trying to tease that apart too. What is the role of geography? Is there a microbial terroir to cabbage? And at this point we don’t know yet. We’re just starting to do some of those experiments.

TWILLEY: Ben told us all of these questions. And then he had an idea. After all, he knows we’re all about microbes here at Gastropod. Why not get us to do some of this research for him?

WOLFE: If you wanted to test our idea you could buy different cabbages from different sources, ferment them in the same way and see what happens. I bet they’ll be different.


GRABER: First one was from Brookford. Second one was from Assawaga. This is the one from the Asian market, right near the farmer’s market. I did what Ben said—

TWILLEY: I did not mainly because I live on the other side of the country from Ben. And after talking with Kevin, I was worried about my kimchi exploding in the mail!

GRABER: So I was in charge of the kimchi making—all three giants jars of it. I bought two Napa cabbages at the farmers market, one from a farm in New Hampshire and one from Connecticut. And I bought another massively huge Napa cabbage from an Asian grocery store in the same neighborhood.

GRABER: Okay, so now I’m gonna slice them up. Probably the hardest part of making kimchi is massaging the salt into the chopped cabbage. SOUNDS OF MASSAGING CABBAGE.

WOLFE: Which by the way is great for stress relief.

GRABER: It is actually hard. You have to really crush and smash it to break up the cell walls and release water and sugars. SOUNDS OF MASSAGING CABBAGE.

WOLFE: Yeah, in mid semester in one of my classes we always make kimchi because it’s such a great way to get out your stress by you know mushing up that cabbage.

TWILLEY: So you got rid of all your stress with that first step—but then it sounded as though you ran into other challenges

GRABER: Let’s see about this weighing down part. SOUNDS OF MOVING PLATES

GRABER: Yeah, I had to weigh down the salted, massaged cabbage for a couple of hours. And I was having a hard time finding something to put on top of the plates.

GRABER: SOUNDS OF MOVING PLATES. Now let’s see what heavy things I have. I’m not sure I have so many heavy things in my cupboard. Here’s a jar of peanut butter.

GRABER: But that wasn’t the worst of it—I worried I messed up the science.

TWILLEY: Cynthia, we are a show about the science of food. This is shameful. What did you do?

GRABER: Well, as you might remember, NIcky, you and I were about to meet up in New Haven to give a talk and do some reporting, and before that I had a wedding in Baltimore, so I had to rush to make three jars of kimchi before heading to the airport. And so I just quickly—well, honestly, I cut all the cabbage on the same cutting board, and I think maybe I forgot to wash the knife in between. So I might have cross contaminated the cabbages, and gotten the microbes from one into the other’s kimchi batch! Which I did admit to Ben.

WOLFE: Yeah. If the cabbage really is the source of the inoculum for these fermentations, then we’ll still see big differences, yeah. But you’re right. Those are some… some small errors in your experimental design.

TWILLEY: And this is why we’re podcasters rather than bench scientists.

GRABER: Totally true. And then to finish up making kimchi, I made a paste out of garlic, ginger, sugar, fish sauce, and red pepper flakes. And mixed that up with the rinsed off cabbage and chopped daikon and scallions. And then the fun continued—

GRABER: Okay. I am now mashing the different kimchis into glass jars and smushing them in so that the brine will rise to cover them. SMUSHING SOUNDS. And I think I may have grated my knuckles a little bit as I was grating the garlic. So I’m holding all of the garlic and spicy peppers. Really fun. SMUSHING SOUNDS.

TWILLEY: But you had to use your hands to do the mixing because Lauryn told us that’s how kimchi has to be made

CHUN: There’s no kitchen tool that’s going to be the proper thing for you to mix it. You’ve got to just use your hand. And in Korea there is this word, son-mat, which means your hands can taste. And I think that really comes from this idea of kimchi making and using your hand to mix and massage the seasoning into the kimchi.

TWILLEY: So your hands are worn out, grated, and on fire from all the spicy salty juices. But you weren’t done.

GRABER: Yeah. Every day, you’re supposed to check the jars, and then gently push the vegetables down with a spoon to make sure the brine is still covering them. I personally enjoyed checking the kimchi, but my partner Tim wasn’t too fond of the smell that enveloped our kitchen each morning.

GRABER: OPENING JAR. LIQUID AND BUBBLE SOUNDS. If I push this down too much, I think the liquid’s gonna overflow. That’s got some pretty serious bubble action going on.

TWILLEY: So you were doing this for science, Cynthia. But Kevin says that in Korea, people—mostly women—have been doing basically this exact same thing for thousands of years.

KIM: Well, historically speaking kimchi has been—some form of fermented vegetable has been found since prehistoric times

GRABER: Historian Michael Pettid wrote a book called Korean Cuisine, An Illustrated History, and in it he wrote about Chinese records from 2000 years ago describing the fondness of the people from the Korean peninsula for fermented foods such as kimchi. But nobody knows exactly where it was invented.

KIM: Some scholars have said that kimchi is a Korean invention in itself. Some people have said it comes from China and the root of kimchi is the pickled fermented Chinese vegetables that you find. And so the history of kimchi is also quite political and contested, as is a lot of food histories.

TWILLEY: Either way, kimchi developed early on as an essential way to preserve vegetables for the long winter ahead. Each household would get through about 150 heads of cabbage in the form of kimchi each year.

KIM: But the kimchi that prehistoric Koreans might have had looks very different obviously than the kimchi that we see today.

TWILLEY: In his book, Michael Pettid quotes a writer in the 15th century referring to kimchi as a golden yellow vegetable. Not red. And the reason it wasn’t red is that there weren’t any chile peppers in Korea. They’re a New World crop.

KIM: The introduction of red pepper comes at the end of the 16th century through the Japanese, who I think got it from the Portuguese.

GRABER: Before chiles, kimchi was spiced with garlic, ginger, and Chinese peppercorns.

KIM: So the spice previous to the introduction of chili peppers might have come from the peppery greens, like mustard greens, the different spices, like for example turmeric. And of course the indigenous spices to the Korean Mountains. But it wouldn’t have been the sort of red pepper spicy that we associate with kimchi today.

TWILLEY: But as soon as chile peppers were introduced, they caught on. Koreans loved the red color chiles gave the dish—red was seen as an auspcious color that would help drive away evil spirits and bad luck.

GRABER: But the kimchi that Koreans were turning red with those new chile peppers, it wasn’t just made of cabbages. And not all of the recipes use fish sauce. There are all kinds of kimchi.

CHUN: So it’s like something like two hundred just foundational recipes. And I kid you not when I say that every Korean family always had their kimchi recipe.

TWILLEY: Kevin’s seen kohlrabi kimchi and green onion kimchi.

KIM: That’s something that my mother absolutely loves and would make a lot. And a lot of it is very regional. So for example my mother’s hometown is Pusan, which is a port city and so it’s very laden with different types of fermented seafood. She might use fermented brined shrimp. And then also whole oysters and other types of shellfish. But then if you go to the sort of colder climates you might see very little seafood, particularly in the mountainous regions.

GRABER: And because Korean families relied on kimchi for their winter vegetables, because they ate so much of it, it didn’t make sense for each family to make their own jars. It wasn’t efficient. Instead, they’d get together in the fall for huge kimchi making parties.

KIM: It’s a very communal experience. It comes from the process known as Kim Jaeng which in Korea is the traditional time, mostly in the fall, where whole families, neighborhoods would come together to make kimchi for the winter months.

TWILLEY: This still happens today. Some of Lauryn’s earliest memories are of this group kimchi fest.

CHUN: You know what I call a kimchi block party if you will. So one day of just purely brining and then the next day of rinsing and then seasoning and then layering and putting away in these earthen earthen gigantic jars.

GRABER: I, of course, didn’t have gigantic earthen containers. I used Mason jars, like most people do today.

KIM: So the kimchi onggi or these clay pots that a lot of times would hold the kimchi were made for regulating the temperature. Most traditionally they’d be half buried into the ground to maintain a constant cave-like temperature to help it ferment appropriately.

TWILLEY: So Cynthia, you did not have these proper clay vessels or a backyard burial, so did your kimchi actually… like turn into kimchi?

GRABER: Well, it certainly it looked like kimchi, it smelled like kimchi, and it bubbled like kimchi I’ve bought in the past with that kind of fizzy tang. But I have to say, I was still worried I’d be poisoning anyone I fed it to. Still, I filled little jars with samples of all three of my kimchis—this time I used clean spoons for each one, to try to make up for my earlier mistake. And I brought all three samples over to Ben and Esther.

TWILLEY: And you confessed to your sins of unscientific cross contamination, and you were forgiven.

ESTHER MILLER: It’ll be fine. We can plate it out and see if there’s any differences. So—

WOLFE: So what we’re going to do for your three experimental kimchis, we’re gonna plate them on media that will grow what are called lactic acid bacteria, which we’ve talked about before. And we’re also going to plate them on a medium that will grow yeasts.

GRABER: Unlike me, Esther is indeed a real scientist. So she sprayed all the surfaces down to sterilize them. SPRAYING SOUND She lit a Bunsen burner to keep the air circulating away from the plates so we wouldn’t drop other microbes on them. LIGHTING SOUND. And she carefully plated out drops of liquid from each of my three jars.

MILLER: So I’m just gonna have 20 micro liters of some of the liquid from each of your different kimchis. Mmm. CLANKING. They’re really good color.

TWILLEY: Your kimchi might have looked nice, but it turns out, you were making mistakes you didn’t even realize you were making.

MILLER: So did you standardize how you cut the cabbage?

GRABER: No, that didn’t even occur to me.

MILLER: Yeah. Because I know some people have commented that if you cut the cabbage more than you releasing more of the sugars. So then you could promote the growth of different things. But I think after you’ve mushed it all up, it’s probably—it’s probably pretty even.

TWILLEY: Ben is one of the nicest human beings on Earth, and even he couldn’t sugar coat your scientific performance here, Cynthia.

WOLFE: We’ll give you—.

MILLER: Oh I think—.


MILLER: I’m sure we’ll see some difference.

GRABER: But he thought as actual kimchi all the samples looked pretty good.

WOLFE: It looks like wonderful kimchi. It really does.

GRABER: I think maybe I won from a cooking perspective.

WOLFE: Yeah. You got a culinary A+.

TWILLEY: Like I said, one of the nicest human beings.

GRABER: But you know even despite my scientific failings, the samples did all smell different.

WOLFE: Well, okay. So we already have some interesting sensory differences very qualitatively. I think this one smells much more less pungent, more rounded, almost like a little sweet. But then go over to the Asian market after that one.

GRABER: Oh, yeah.

WOLFE: More cutting.

GRABER: SNIFF. It smells—it smells a little more acidic, I think? So maybe Ben and Esther would actually find some interesting results. Esther put drops of the diluted kimchi juice on different plates.

MILLER: And then we’ll use the beads to spread it around. So we get like a nice even coverage of bacteria and yeast across the whole plate.

WOLFE: And this is where it gets noisy. SHAKING SOUND. These will grow up for about a week and then we’re going to meet again in November to talk about the results.


TWILLEY: So, Cynthia, your little kimchi experiment was designed to see whether different cabbages from different farms ended up making kimchi that had different microbes. But what I’m curious about is what difference different microbes would make to the texture and taste of kimchi. I mean, they’re all lactic acid bacteria at the end of the day, so why does it matter which exact ones you have?

WOLFE: Not all lactic acid bacteria are created equally. Some of them produce mostly just lactic acid, which is the main preservative in kimchi. But others can produce things like carbon dioxide in large quantities to make that really fizzy quality. Some of them can make a little bit amounts of acetic acid, which is vinegar. So you can really get a completely different flavor profiles based on the bacteria you have.

GRABER: So I had to wait for the results of my kimchi for a couple of weeks, and then I headed back to Ben’s lab at Tufts to find out the results.

WOLFE: OK. I’m gonna put this here. I’m gonna throw on a lab coat. There’s Esther.

GRABER: Great. I’m going to put this here. Okay. Nicky, I’m gonna put you down. So you’re gonna hear kind of from a distance.

TWILLEY: I did not want to be left out of this kimchi party, so Cynthia had me on speaker.

MILLER: So you can see these are the plates that have all of the different colony types on them. So you can see there’s like large round ones with dimples in the middle. Really, really tiny white ones. Some that are off white. You get very good at white descriptions. LAUGHTER.

GRABER: The different puffs and specks of white or off white represented colonies of different lactic acid bacteria.

MILLER: And then I took like a scoop here and extracted the DNA.


WOLFE: So what’s cool is we see unique microbes in each of the fermentations. So there’s some microbes that are across all three of the ferments. So this one right here, for example, is Lactobacillus plantarum. Super common in vegetable ferments. And we found that really abundant in all of them. And another bacterium we found across all three of the ferments is Lactobacillus brevis. But one bacterium that we found only in the Assawaga is the Lactobacillus curvatus. And you can tell that one does look distinct. It’s much smaller. The colonies are a little bit more see through. It’s a little bit more beige. And then the other bacterium that we didn’t find in all three ferments—it was only in the Asian market and the Brookford—is Leuconostoc.

MILLER: Yes. So the Leuconostoc is one that you find at the beginning of a lot of ferments. So it’s one of the first early acidifiers. So it’s really cool that we found it in yours when they’re sort of progressed. Because I’ve been looking for it. And I never find it because it’s always out-competed by the Lactobacillus.

GRABER: I thought these results were fascinating and I was glad Esther was excited, but mostly I was super relieved that even despite my lack of scientific rigor, there were actually differences. And even more importantly for my eating enjoyment, apparently all three looked like communities of pretty happy kimchi-making microbes.

WOLFE: Some cases we actually see ferments where you get a tenth or a hundredth of the number of colonies and those’d be bad or failed fermentations.

MILLER: And they’re looking really good and really diverse. Sometimes we don’t really find a very diverse community.

TWILLEY: I am so proud of you, Cynthia!

GRABER: Thanks! And that wasn’t the only cool thing about my microbes—Ben and Esther were particularly excited to find a type of yeast in one of my kimchis.

MILLER: So on two of them, we didn’t see any yeast, but on the Brookfield one we see this bright pink Rhodotorula. It’s so beautiful.

GRABER: They’re like these really cool, bright pink-orange polka dots.


WOLFE: It’s like American Apparel spandex, pink. Right? It’s so pink.

TWILLEY: Despite its obvious aesthetic appeal, Ben says the current science seems to suggest that yeast might not actually be a great thing to have in kimchi, because it might make it slimy. But everyone was very excited about Cynthia’s bright pink yeast.

WOLFE: I mean, I love yeast. I’m a fungal person by training. So anytime I see fungi in a largely bacterial community, I get really excited.

MILLER: I mean you just have to look at a sea of tiny white colonies and then something pink is there and we’re all freaking out. We’re like, something different!

GRABER: Luckily I can’t see anything bright pink in the actual jar of kimchi, and it doesn’t feel at all slimy. Basically, all three look like kimchi. They do smell and taste very slightly different, but they’re all really good.

TWILLEY: So what overall did we contribute to science here? Give me the abstract.

WOLFE: The overall results of this experiment suggests that where you buy your cabbage from means you get different microbes. You actually can—maybe you call it microbial terroir of cabbage. I don’t want to necessarily say that’s what we found. This is only three cabbages in your kitchen and we’d have to do a larger study. But it does support work that Esther has done in the past, showing that different farms have different microbiologies that then affect the ferment. You had real world conditions in your experiment and still the differences would shine through, which is fantastic.

TWILLEY: Real world conditions are great, but Ben said to really, conclusively figure out the microbial terroir of kimchi, he’d have to do a much larger and more controlled experiment.

WOLFE: I mean, I would love to have 75 farms throughout New England that would grow the exact same variety of cabbage in the exact same way for us that we could then bring back to the lab and then ferment in very controlled ways. And even show that, you know, northern Vermont has a different microbiome than western New Hampshire, for example. But to get people to grow cabbages at all those sites would be really, really challenging.

GRABER: But Ben has a question that goes back further in the process. Remember, Ben told us these lactic acid bacteria are rare in the field, they don’t love cabbage leaves—in fact, they die on the sterile cabbages. So, to go back to the question that started his whole research project, where do these microbes come from?

TWILLEY: As it happens, he and Esther are in the middle of testing a theory about that.

WOLFE: Yeah. So what we’re trying to do is find whether lactic acid bacteria that live in insect guts are the ones that are doing the fermentation. So in other words, insects as they’re crawling around on cabbage leaves and pooping and chewing, are they depositing important bacteria that will eventually be the ones that we’re seeing right here that are doing the fermentation? So we don’t actually have an answer for that yet. But there’s a lot of insects being smushed up for science to answer that question.

TWILLEY: Count yourself lucky you didn’t have to smush insects, Cynthia. It could have been worse.

GRABER: It wasn’t so bad in the end, I’m going to keep making kimchi at home. Maybe I’ll do the daily checking in on it when Tim’s at work.

TWILLEY: Ben and Esther are going to keep trying to solve these kimchi mysteries.

WOLFE: The origins of most of the bacteria that are in ferments are poorly known. We don’t really know where all these things come from, even though we rely on them for fermentation. And again, we don’t know their individual roles or the slight differences in their aromas they make or do they ferment at different rates? We would have to test that. But yeah, more science needs to be done.

TWILLEY: Meanwhile, you have three giant jars of kimchi at home.

GRABER: Good thing I really like it.

TWILLEY: But seriously, that’s a lot. How have you been eating it all?

GRABER: I do kind of traditional things like put it in rice with tofu. But I particularly love it—trust me on this one—I love it on toast with peanut butter.

KIM: Yes I’ve heard that combination, that kimchi and peanut butter combination. Yeah.

TWILLEY: Yeah, OK, but it’s not traditional. The most common way to encounter kimchi in Korean cuisine is just as a side, served cold.

KIM: The traditional Korean table setting is rice, kimchi, some kind of soup and then pickled or seasonal vegetables as well. So that’s the sort of classic setting that you will see—breakfast, lunch, and dinner. It also could form the backbone of different soups. So for example kimchi jigae or kimchi stew is something that I love and and that I crave whenever I go back home to visit my mother. That’s one of the first things she cooks for me.

GRABER: But my seemingly strange PB & Kimchi combination isn’t actually all that out there. Koreans are putting kimchi in everything these days.

KIM: The younger folks are now experimenting, right? So they’re putting kimchi in things like pizza or hamburgers or putting it on top of fries, or you know adding it to pasta to make kimchi carbonara, which is delicious by the way. Or kimchi grilled cheeses, which is also delicious by the way.

TWILLEY: Kevin says there’s lots of hand wringing about the younger generation of Koreans becoming McDonalds-ized, but actually from his research, yes, they’re eating Western foods, but they’re bringing kimchi along with them.

KIM: That’s sort of the osmotic nature of kimchi that you know you could use it as a condiment, you could chop it up and put it into various things. And you know I’m fascinated to see where kimchi ends up almost on a daily basis whether it’s pasta or pizza or hamburgers or in snack foods. I remember seeing kimchi-flavored potato chips.

GRABER: That’s in Korea. But these days, you’ll find kimchi in more than just Korean restaurants in the US, too. How did it get so popular here?

TWILLEY: There’s a few different reasons. One of them is the Hart Cellar Immigration and Nationality Act of 1965.

GRABER: The act opened up immigration to the US and totally transformed the immigration system. Not just for Koreans, obviously, but it had a huge impact—about 95 percent of the Koreans in the US are from families who immigrated after 1965.

TWILLEY: That’s kind of a bottom-up, organic approach to spreading the kimchi love. But Kevin says there’s a more intentional push behind the popularity of kimchi today.

KIM: So the top-down approach has been—and this is something that I’ve been looking at in my research—is the way that kimchi has acted as soft power or, like I say, kimchi diplomacy. Right? So the Korean government actively promotes Korean food and food culture abroad as a form of soft power diplomacy. And so Korean food, Korean dramas, Korean music in the form of K pop has been really pushed by the South Korean government and South Korean multinational corporations to promote the benefits of kimchi for example and to sell kimchi.

GRABER: A major push for kimchi diplomacy took place in 1998, at the Olympics in Seoul. Apparently officials in Seoul were really worried that Western Olympians and visitors would think kimchi was too stinky. But they also really wanted to promote kimchi.

TWILLEY: So they made kimchi one of the official foods of the Olympics. But they also made a rule that anyone interacting with foreigners during the Olympics had to brush their teeth thoroughly after every meal.

GRABER: And apparently this careful kimchi consideration paid off—sales of kimchi skyrocketed after the Olympics.

TWILLEY: Kimchi diplomacy is a long game in Korea. When the first Korean astronaut went to space in 2008, she took kimchi with her. The Korean government had invested years developing space kimchi—bacteria-free kimchi that would not explode in space but would still give that taste of home. And of course promote kimchi to the rest of us.

GRABER: Another thing that’s added to kimchi’s popularity is the idea that the microbes in it might contribute to the health of our guts.

KIM: And a lot of that science comes from Korean scientists in the early 90s. There was a real boom in kimchi research then. And you see all kinds of peer-reviewed scientific studies that looked into the nutritional benefits both of the lactic acid bacteria, the sort of gut friendly bacteria that we hear about all over the the the media today.

TWILLEY: So, put all this together, and Korean food has become much much more popular in the US. You get the rise of the Momofuku empire, which started as a noodle bar in New York City in 2004. And then in 2008, here in LA, chef Roy Choi introduced the iconic kimchi taco.

ROY CHOI (Splendid Table): I think, you know, nobody can hate on a taco, you know, so that right there was already a vessel that made people look and care and take a chance.

GRABER: That was Roy on NPR’s Splendid Table a few years ago. Roy created a perfect LA-style mash-up: Korean barbecue of pork or beef, butter-sauteed kimchi, chiles, soy sauce, garlic, lime, all wrapped up in a corn tortilla. I haven’t had the pleasure, but it does sound delicious. People chased his food truck down based on the location broadcast on twitter, critics raved, it was a huge success.

TWILLEY: Nowadays kimchi is like sriracha—something that used to be exotic and slightly scary that is now all over American menus at big chains like California Pizza Kitchen and TGI Fridays.

GRABER: Everyone’s eating kimchi. Americans are now enjoying it, Koreans haven’t given it up.

TWILLEY: Although Kevin says it is kind of annoying that kimchi prices have risen alongside its popularity.

KIM: I remember one of my real catalysts for going into researching kimchi came when my younger sibling and I, we were walking around a fancy farmer’s market and we saw someone selling a tiny jar of kale kimchi for like eight dollars. And that’s not to say that that person you know didn’t put love and care into that kimchi, but as Korean Americans, you know, that was sort of antithetical to how we remember kimchi as something that was communal, that was shared.

GRABER: So Kevin launched his own communal fall kimchi making party.

KIM: You know, we’ll get together, my younger sibling and I, we will buy boxes and boxes of Napa cabbage from our local Korean supermarket. And we’ll invite our friends and family over, we’ll make kimchi, we’ll hand it out to our neighbors.

TWILLEY: That’s the power of kimchi—it’s about community, and also, at a very fundamental level, it’s about being Korean. This is a message that’s pushed by the government with their kimchi diplomacy, but it’s also everywhere—in graphic novels and TV dramas and all over popular culture.

KIM: So you might see kimchi being shown in a K pop music video, for example, to signify the Korean-ness of a particular group.

AUDIO: Let Me Eat That Kimchi

GRABER: There’s a great video online of a performance at Korea Day in New York—

AUDIO: We’re cooking up the kimchi / Cabbage in a pot / Got to make it extra spicy  / Chile make it hot

TWILLEY: Like we said, back when Kevin and Lauryn were growing up, kimchi was seen as peculiar and stinky. And now it is hipster and foodie and supposedly the secret to eternal gut health—it’s basically fire.

KIM: So I tell my friends and colleagues that I find it interesting that the people that were making fun of my kimchi fried rice when I was in elementary school are now asking me for kimchi recipes. I find it to be quite hilarious.

GRABER: As Kevin pointed out, sometimes the older generations of Koreans and Korean Americans worry what the younger generations are eating. But both Lauryn and Kevin say—nothing to worry about. Kimchi is eternal.

CHUN: It’s still always going to be around. Like you can’t be a Korean—whether you like the taste or not, kimchi is just part of being Korean.

TWILLEY: We’d like to thank the Alfred P. Sloan Foundation program for the Public Understanding of Science, Technology, and Economics for their support of Gastropod and of this episode.

GRABER: Thanks this episode to Kevin Kim, a doctoral student based at the University of Maryland—and thanks to our fabulous former intern Emily Pontecorvo who helped out with research.

TWILLEY: Thanks also to Lauryn Chun of Mother-in-Law’s kimchi and The Kimchi Cookbook, and also our ongoing and eternal gratitude to our very own microbiologist, Ben Wolfe of Tufts University, and his kimchi-obsessed graduate student Esther Miller.

GRABER: We’ll be back in two weeks with our final episode of 2019! Don’t worry we promise we’ll be back in January 2020, and this last episode is going to be awesome.

TRANSCRIPT What’s CRISPR Doing in Our Food?

This is a transcript of the Gastropod episode, What’s CRISPR Doing in Our Food?, first released on October 7. It is provided as a courtesy and may contain errors.

NEWSCASTER 1: Cue the worldwide CRISPR frenzy! At the University of California, scientists used a form of CRISPR to edit mosquitoes so they can’t transmit malaria. Their colleagues are modifying rice to better withstand floods and drought.

NEWSCASTER 2: Scientists say it could someday eliminate inherited diseases like some cancers, hemophilia, and sickle cell anemia.

NEWSCASTER 3: Researchers in Massachusetts have created piglets that might one day provide livers, hearts, and other organs for humans. They used a gene editing technology called CRISPR to remove viruses from pigs that could cause diseases in humans.


SCIENTIST: This has CRISPR in it.

NEWSCASTER: So this is what’s revolutionizing science and biomedicine?

CYNTHIA GRABER: Wow, listening to that, it seems like scientists have discovered something that is going to change basically everything.

NICOLA TWILLEY: If you’ve been following the news at all, this whole CRISPR thing gets waved around like it’s literally a magic wand. But we at Gastropod are always a little suspicious of magic, especially when it comes to science—so we decided to get to the bottom of it.

GRABER: And find out what CRISPR means for the future of food. That’s right, this is Gastropod, the podcast that looks at food through the lens of science and history, I’m Cynthia Graber—

TWILLEY: And I’m Nicola Twilley. And this episode we are talking about CRISPR. Which I will say has a nice name, I like crispy things in general. But isn’t CRISPR just genetic engineering, like GMOs, with a shiny new rebrand for today?

GRABER: Right. How is it different from or the same as what scientists have already done to genetically modify foods? What is CRISPR?

TWILLEY: And will it really change what we eat? Or are we eating CRISPRed foods already and we just don’t know it.

GRABER: Should we be worried or excited? We promise you, when it comes to CRISPR and food, we’ve got it. Plus, the secret CRISPR in your yogurt.

TWILLEY: The yogurt story is the CRISPR story you won’t have heard anywhere else. And it involves microbes, so, you know, DRINK!


GRABER: So you’ve probably figured out that CRISPR is a gene-editing tool, but we wanted to learn what it is, and how it was discovered. This might sound a little strange, but trust us—to learn about CRISPR, we drove out to DuPont’s dairy culture plant and we met with a yogurt scientist named Dennis Romero.

DENNIS ROMERO: Okay, we’re in Madison, Wisconsin. It’s a kind of a dreary-but-sunny, if that makes sense, day. Winter’s coming. Anyway, we’re on the southeast side of the city, kind of on the corner. This used to be all farmland in the day but the plant which is just across the street was put up in the late 1960s, to make starter cultures.

TWILLEY: “Winter is coming,” I understand, but I don’t remember dairy starter cultures from Game of Thrones.

GRABER: You listeners know that cheese and yogurt is basically milk that’s gone bad, but in a good way. Bacteria have had their way with it. But when I leave milk in the fridge and the bacteria get going, it smells and tastes pretty gross.

ROMERO: Dairy cultures than would be bacteria that were originally found in the milk and over the years were selected and chosen. because they didn’t turn the milk that kind of a kind of funny sour nasty-tasting mess that you’d find, but they actually turned it into something quite pleasant like cheese and yogurt.

GRABER: In the past, someone might have made this discovery and then saved a little bit of the good yogurt to make the next batch. You can still do this today—take some yogurt you like and use it to make more yogurt.

TWILLEY: I have done this, in my one-and-only moderately successful attempt to make yogurt at home.

GRABER: But this is not what industrial yogurt makers do. They buy a package of just the right freeze-dried microbes from a dairy culture company—and DuPont is one of the biggest dairy culture companies in the world.

ROMERO: This red pouch one is called Yomix. It’s used to make any of a number of yogurts. And you just sprinkle this into the cheese milk or the yogurt milk in this case, and stir, and off it goes. It looks like a like a package of instant oatmeal, that’s about the size. And think about several billion bacteria in there that could turn, you know, many, many gallons of milk into yogurt.

TWILLEY: Dennis and his colleagues at DuPont have isolated and catalogued all the strains of all the bacteria that you might want to use to make yogurt. They know which strains of bacteria are the ones that will give you that nice, sour tang, and which make your yogurt more creamy, and which can help make it thicker or thinner.

ROMERO: In this catalogue, we’ve characterized these strains for these properties. And we give these recommendations to our sales people who talk with our customers, the cheese makers and yogurt makers, knowing what the bacteria or the culture can do, then they can recommend a specific culture to them to make what they’re looking for.

GRABER: All these bacteria that Dennis studies and that DuPont sells—they’ve been carefully selected to also be super fast and super reliable. The customers can make the same texture and taste of yogurt each time. This means the dairy culture business is big business.

ROMERO: Oh, how big? I don’t have the exact numbers. That’s something that I have no idea. I mean it’s hundreds of millions of dollars worth—even more I guess.

TWILLEY: But sometimes something bad happens at the yogurt factory. The company is using the cultures it bought from DuPont, but their yogurt is just not coming out right.

ROMERO: On occasion it can be kind of chunky and grainy looking. That’s probably a bacteriophage that attacked the fermentation at some point in time.

GRABER: This is the nemesis of yogurt culture bacteria. Bacteriophage are usually just known as phage, and a phage is a tiny, tiny virus that attacks bacteria.

TWILLEY: You think microbes are small and everywhere, but phage are even smaller, and even more ubiquitous. There are more phage on earth than every other organism, including bacteria, put together. And phage cause a trillion, trillion infections in bacteria every second.

ROMERO: That’s the one thing that will disrupt the cheese maker or yogurt manufacturers’ process more than anything else. You know, if you ever catch the flu, you don’t feel too good. You’re kind of slow, you’re kind of sluggish. Well, the bacteria if they catch the flu, they can feel that way. Worse yet, they tend to explode. So, not a good thing.

TWILLEY: Sometimes my head feels like it’s going to explode when I catch the flu. But actually exploding is a whole other level of bad.

GRABER: Dennis took us into his lab and introduced us to Annie Millen, a scientist with his group, and she showed us a clear circle of agar gel on a petri plate. They’d grown yogurt bacteria on the gel, and then infected the bacteria with phage.

ANNIE MILLEN: This phage is pretty deadly. So on this one, there’s still the hazy bacterial lawn in the background. But there are really large circular zones of death where it’s just clear.That’s all where the bacteria has died, and it just looks like nothing. because there’s nothing there anymore.

ROMERO: Can you hear the bacteria? “Ahh, I’m popping, I’m bursting.”

GRABER: Obviously, it’s not a great thing when your yogurt-making bacteria explode, because they’re no longer making your yogurt.

TWILLEY: In the past, when a yogurt company would call Dennis and say “Oh no, our starter cultures aren’t working and the microbes are all exploding”—the first thing Dennis would suggest was that they clean the entire factory from top to bottom.

GRABER: Because Dennis wants the yogurt maker to try to get rid of the phage. Though of course that’s pretty tough given how tiny and plentiful they are.

TWILLEY: And then Dennis would give them a new set of cultures. But they weren’t the same strain—he’d deliberately give them different strains of bacteria that could make the same yogurt, but that might be tougher than the microbes that exploded.

ROMERO: One of the unique things about them is that they have different sensitivities to these bacteriophages. And just like human beings, you know, Nicky could catch the flu. But, Cynthia, you could be sitting right next to her but you’d be perfectly fine because you are immune to whatever she’s got. And the bacteria kind of behave the same way. The key point here is you have to find two strains that will do the same thing except for their sensitivity to a given bacteriophage.

GRABER: Okay. So this is what’s been going on for a really long time in the yogurt business. Phage kill your batch of yogurt, you buy a new strain of yogurt culture, and so on. But then, a few years ago, something really exciting happened.

ROMERO: For me, this is actually kind of an interesting story of how science actually happens. I mean it’s not something that you plan for, you know, and say today I’m going to discover CRISPR. I wish I could have said that but, no, that’s not really the way it happened

TWILLEY: The context here is that it was the early 2000s, and genetic sequencing had got faster and cheaper and so DuPont decided to sequence some of their key yogurt bacteria.

ROMERO: We were looking for a way to identify our different strains in a very quick and rapid way. Because, you know, they don’t sit there and go “Hi, I’m Bob,” ‘Hi, I’m Steve,” whatever. And so there’s a lot of work that has to go on to determine, yes, this is strain one, strain two, strain three.

GRABER: And in doing these genetic sequences to try to identify their dairy culture bacteria, Dennis and his colleagues noticed these kind of weird stretches of DNA, a whole bunch of them. Nobody really knew what they were, but they’d been observed before, and so people called them this complicated name: Clustered Regularly Interspaced Short Palindromic Repeats. CRISPR.

ROMERO: It was a very short repeated sequence, of the same sequence repeated over and over and over again, with something that was seemingly nonsensical stuck in the middle of each of these little repeats.

TWILLEY: Like everyone, Dennis and his colleagues had no idea what these nonsensical CRISPR sequences did. But they realized they might make for a good fingerprint.

ROMERO: So we started to sequence more of them and, oh, look, you know, there’s something interesting. There’s subtle differences between them. That little piece of nonsensical DNA—you can line these up, because some of the strains have the same ones. And then at some point they start having different ones.

GRABER: At the time Dennis and his colleagues had another research project going on. They were taking cultures of yogurt that had gotten sick from phage, and they’d see if any of the bacteria lived through the infection. And some always did.

TWILLEY: So they took a look at these survivors—the phage-resistant bacteria—and they noticed a difference in the CRISPR section of their genome.

ROMERO: On one end, the phage-resistant variant had a couple extra pieces inserted in there. And I think it was that moment where, like, for any scientist there was like the, “Aha!”

GRABER: The aha was the idea that this tiny bit of code, the part that they had no clue what it did—this might be the part that made the bacteria able to survive an attack from that particular phage.

ROMERO: And my first thought was, can it be that simple? Think about this bacteria having 2 million base pairs that tell it what to do how to live and how to work. That two little pieces of DNA, about 30 nucleotides or 30 letters stuck in the correct place, can actually confer the ability of this bacterium to resist a bacteriophage, so it lives.

TWILLEY: This is Dennis and his colleagues’ breakthrough. They are the ones who figured out that maybe these CRISPR sequences in bacteria that no one understands what they do—maybe they’re to do with immunity to phage.

GRABER: So then the first order of business to test this idea is to figure out where the sequences come from.

ROMERO: So when we took a look, the only difference that we could tell, at least from what we were looking at, was: the sequences in the CRISPR array came from the bacteriophage. Oh, that’s interesting.

TWILLEY: Those nonsensical repeats in the bacteria’s genome? They were little chunks of phage DNA.

GRABER: To test whether the phage DNA is what helps with immunity, they did an experiment to try to figure out if the bacteria that survive a phage attack have bits of code that match to that exact phage.

ROMERO: So it’s really, really simple. You take the bacteriophage, you mix it with the bacteria, and then you throw it on this agar nutrient plate and see what lives. And you take what lives. And we look at the CRISPR loci—and oh look, it’s got a couple, one or two extra spacers in it again. And you look at the spacers and they come from the bacteriophage. So now you have this—hey, the two are connected in some way shape or form.

GRABER: So basically, somehow, it seems like that tiny bit of phage DNA gets into the bacteria, and the bacteria then become immune to that phage.

TWILLEY: Which is extremely exciting. Dennis’s next experiment was designed to confirm that that is really what’s going with CRISPR. If he inserted a little piece of phage DNA—one of those little CRISPR sequences—into a yogurt-making bacteria that was not immune to that particular phage, would that bacteria become immune?

ROMERO: And surprise, surprise—well, maybe not a big surprise. Yes, it was. Oh, okay. So now it’s absolutely clear: without ever having seen the bacteriophage, we can provide this immunity, this resistance to it.

GRABER: The way that this happens out in the real world is: some of the yogurt-making bacteria survive a phage attack. And the ones that survive keep a little mug shot of the evil phage that tried to kill them. In this case, the mugshot is a snippet of phage DNA.

TWILLEY: The survivor bacteria hold onto this mugshot in case they ever meet that evil phage again. And they stick in their DNA, for safekeeping, right next to where they keep their phage-killing weaponry.

GRABER: And one of those weapons? It’s a tiny protein called Cas9—CRISPR-associated protein number 9. And what this tiny little protein does is it snips. It’s basically a pair of scissors that just slices straight through phage DNA.

TWILLEY: And when your DNA gets sliced, you don’t really work as well. In fact, you are often toast, especially if you are a phage.

GRABER: The whole system together is super cool: mugshot plus scissors equals immune system.

ROMERO: People have described the CRISPR array as being something like memory for the bacteria. And it really is because it’s a memory of what viruses, in this particular case, what phages that they’ve been exposed to. So that in the future should the daughter cells of that CRISPR-ized—that’s what we call it—bacterium meets that phage again, it knows what to do to protect itself.

TWILLEY: This system is actually found in a lot of bacteria, although not all. It’s not unique to dairy cultures though, but, because we love yogurt and cheese and the microbes that make them so much, that’s where we first noticed it

GRABER: Dennis had been looking for a way to fingerprint his bacteria strains, but this—this was something else altogether.

TWILLEY: This was transformational. Dennis could use this natural bacterial immune system, CRISPR, to cure his customer’s sick dairy cultures.

ROMERO: So, cool. This makes life easy for us. So we go through the process of vaccinating or immunizing the bacteria, and then putting them back out there in situations where we know there’s a bacteriophage present, and they perform perfectly fine. It makes life much more simple for us and we can go off and study other things. It sounds ridiculously simple when I put it that way, but that’s what it does.

TWILLEY: Within a year, Dennis and DuPont were immunizing all their starter cultures and selling these CRISPRized microbes to their customers.

ROMERO: Essentially, it’s pretty much just like the flu vaccine. You try to find the most prevalent ones that are impacting the industry at that time.

GRABER: And any time there’s a new phage that appears, they can add that mug shot to the bacteria’s collection, too.

ROMERO: So, in essence—we joke about this—but from the perspective of sensitivity to a bacteriophage, we can immortalize that particular strain.

TWILLEY: Dennis and his team just keep adding new mugshots.

ROMERO: There’s no limit that we found just yet to how many spacers it can acquire. So it just goes on and on and on.

TWILLEY: For the past fifteen years, almost all commercial, industrial-type yogurt—which is basically all the yogurt in the supermarket—has contained CRISPRized bacteria.

ROMERO: We tell this to people. You’ve been eating CRISPRized cultures forever—you just didn’t realize it.

TWILLEY: This is something you never hear in all the hype about CRISPR. We’re already eating it all the time, thanks to the microbes in our dairy.

GRABER: These CRISPRized cultures are totally standard in the dairy industry these days. The yogurt companies are thrilled, DuPont is thrilled, Dennis and his colleagues are thrilled. The yogurt is a better, more consistent texture, they don’t have to add any extra thickeners in case the microbes are falling down on the job, they don’t have to rotate strains of microbes, it’s great.

ROMERO: Yeah, you know, it’s a living system. And one’s ability to control it to some degree so that you get the same thing out every day is a big deal.

TWILLEY: A couple of key words here are ‘living system’ and ‘to some degree.’ We’re talking about biology, so, of course, it’s not 100 percent under human control and the same every time. For one, not all yogurt bacteria even have this kind of immune system, so they can’t be vaccinated against phage. Also, some phage can evolve to beat CRISPR or work around it. But, still.

GRABER: Yeah, still. It’s changed the yogurt business.

TWILLEY: And honestly, that’s kind of the least of it.

GRABER: Right, as you heard at the beginning of the show, CRISPR is actually changing the world. We asked Dennis if he and his colleagues had any idea when they discovered this system what other researchers might end up doing with it.

ROMERO: We joke amongst ourselves that one of the first exercises was we wrote down all these experiments and possible applications and things. And we really went to town with that. What could you imagine that this could be useful for?

TWILLEY: The way Dennis and his colleagues saw CRISPR was as a way to create immunity. So in their brainstorming session, they came up with lots of cool ideas—outside of the yogurt business—where immunity would be useful.

ROMERO: So one of the things I thought was really, really interesting and gratifying for me personally was we had written down: would this be something that could somehow be adapted to confer immunity to things like influenza or HIV?

TWILLEY: Scientists are currently doing exactly that—there’s brand new research using CRISPR as a tool to cure HIV and the early results seem promising.

GRABER: But the part Dennis and his team didn’t predict is that CRISPR would become a tool for editing nearly everything. And that’s exactly what’s happened.

ROMERO: I’m still kind of awestruck by it all because, at least for me, I just—I find this fun. And to be able to come across something like CRISPR-Cas and see the impact that it’s having on life and people in general? I sit there and I think about it and go, wow, I had something to do with that. I mean, how lucky can one be?

GRABER: That’s kind of every scientist’s dream, to see research they’ve been a part of having such a major impact.

TWILLEY: But all this came out of something super non-world-changing—yogurt. No offense to yogurt, which I love, but you know what I mean. So how did CRISPR make it out of the yogurt factory and into nearly every genetics lab in the world?

GRABER: That’s just what what we’re going to reveal next.


GRABER: To answer the question of how CRISPR became the hottest new thing in genetic engineering, we need to take a step back.

JENNIFER KUZMA: Right. Well, since about the mid-1980s, we’ve been genetically engineering plants.

TWILLEY: Jennifer Kuzma is a trained biochemist who co-directs the Genetic Engineering and Society Center at North Carolina State University. And she told us that back in the 80s, before CRISPR, scientists had a couple of ways to insert new genes into plants—but they had no control over where that new gene ended up in the plant genome.

KUZMA: Like, you take a gene from, for example, a fish—and it would land anywhere into the crop that you wanted to place it in, let’s say tomatoes.

GRABER: This very example that Jennifer is using, this is one of the most famous early examples of genetic engineering. The idea was that this cold-water fish called the winter flounder had an antifreeze gene that helped it survive icy temperatures, and this gene could help tomatoes survive frost.

TWILLEY: So scientists put the antifreeze gene in the tomato. And then a bunch of people freaked out about the resulting fish-tomato.

PROTEST CHANT ON NEWSREEL: Hey hey, ho ho, GMOs have got to go!

NEWSCASTER: These protesters want this grocery chain and others to stop carrying foods with genetically-modified ingredients.

PROTEST CHANT ON NEWSREEL: Careful what you put on your grocery shelf!

NEWSCASTER: This man’s costume is meant to illustrate genetically-altered fruit that’s been given fish genes to make it hardier in cold weather. They call it Frankenfood, and they say it’s bad for people, bad for the environment.

TWILLEY: As it turns out, the fish-tomato didn’t do so well in field trials either, so it never made it to market. But that didn’t stop companies from creating all sorts of other GMOs. You’ll maybe have heard of Golden Rice, the rice with extra vitamin A—that comes from scientists inserting a daffodil gene and a gene from a soil bacterium in ordinary rice. There’s also pink pineapples and faster-growing salmon and non-browning apples, all with genes borrowed from different species. You can’t buy all of these yet, but they’re all approved for sale, at least under U.S. regulations.

GRABER: But, really, until now, most of the research on genetically modified foods has been focused on making plants resistant to certain weed killers. That meant that farmers could use those herbicides in the field, the chemicals would kill all the unwelcome plants, but the crops would still be going strong because they were resistant to that weed killer. So you have GM herbicide resistant corn, wheat, soy—and these are all being sold and used today, and if you eat processed foods in America, you are eating these GM crops.

TWILLEY: That might come as a shock to you. Especially because there’s still a lot of public discussion about whether genetically modified crops are really safe—safe for the environment, safe for human health. In the European Union, they’re mostly banned.

KUZMA: Genetic engineering has a pretty rough history when it comes to foods and there’s been quite a bit of controversy over genetically modified foods and whether or not they should be labeled and people seeking to avoid them through buying organic or non-GM products.

GRABER: Proving something is safe in terms of our health is really hard, but so far none of the studies have shown that these GM crops are bad for us. Whether their main use—making crops resistant to weed killers—is an overall win for growers and for the environment or not, is definitely questionable.

TWILLEY: That’s been the story of genetically modified crops up till now. But today, GMOs are sort of old school. The cool kids are all using CRISPR to create new crops. It evolved in microbes, and Dennis and his colleagues still use it in yogurt cultures. But it turns out that, with a little bit of tweaking, the CRISPR-Cas9 system can be used in all sorts of living things.

GRABER: As Dennis explained, there are two parts to CRISPR. There’s a piece that slices, that’s Cas9, and then there’s a piece that recognizes phage DNA, that’s CRISPR. But imagine this—you could put a different piece of plant or animal genetic code instead of phage DNA next to those scissors. Now you can direct the scissors to cut a very precise piece of DNA in, say, a tomato.

YIPING QI: And then you allow the sort of error-prone DNA repair pathway to repair the broken DNA. The result in most cases is a gene knockout

GRABER: Yiping Qi is a genetics researcher at the University of Maryland.

TWILLEY: And this process Yiping’s describing, works like this: instead of hunting down phage and slicing them to death, this tweaked CRISPR-Cas9 system will hunt down the DNA sequence of your choice, and slice it. The sliced DNA tries to repair itself, but usually there’s a kind of scar, where it was sliced, and the gene at that point, where the scar is, doesn’t work anymore. And there you go. You’ve knocked out a gene from the tomato’s DNA—the exact gene you wanted to get rid of. And, unlike the old-school fish tomato style GMOs, you’re not adding any new genes.

GRABER: Dennis and his colleagues figured out how bacteria use this slicing system to kill phage in the mid-2000s, and they published papers on it in 2007. About five years later, two different groups of scientists both claimed to have been the ones to figure out how to use this CRISPR system to edit something other than yogurt-making bacteria—and they’re fighting about it in court. Because it seems so flexible and so useful in genetics and human health, and all of this promises to bring in so much money—it’s a huge patent battle.

TWILLEY: But what do we care about here at Gastropod? Obviously, our friends, family, world peace, but, you know, mostly food! And CRISPR is set to transform our crops, too.

QI: I mean that CRISPR has been really put in to many, many crops. Almost nearly all the crop plants which you can transform, such as the wheat, maize, and sugar cane, and tomato. Many, many—like even carrots, which I have worked with a collaborator.

GRABER: This is a different technique, and it’s being used in a different way.

KUZMA:  With transgenic technology, it was very costly to bring a crop to market. Very costly to engineer it. With CRISPR technology, we’re seeing a wider variety of products. So not only, you know, your commodity crops like corn and soybeans and cotton but more minor vegetable and fruit crops.

TWILLEY: Including ones that are so minor that you may not have even heard of them. We’re talking about crops that don’t necessarily even make it to the store right now.

JOYCE VAN ECK: So they’re referred to as either underutilized or orphan crops.

TWILLEY: This is where we’re going next. To the crop orphanage, where some of the most minor fruits and vegetables of all are about to be rescued thanks to the magic of CRISPR!

VAN ECK: Yeah, these orphan crops out there, without anyone to care for them. LAUGHS

TWILLEY: And we’re going to visit the orphans with Joyce Van Eck. She’s a bio-engineer at Cornell.

GRABER: Though she’s laughing, Joyce does care about them. These crops are orphans because they’re not the type of plants we grow in a big monoculture. They’re tough to grow on a large scale, so they’re not traded internationally, and they don’t get a lot of research love.

TWILLEY: Joyce has picked out a particular orphan to adopt. It’s called the ground cherry, and it comes from the same family as peppers and tomatoes. It’s like the underachieving, less loved sibling.

VAN ECK: It’s this cute little yellow fruit that is surrounded by a husk. It’s kind of like, if you think of a little fruit in a balloon. And it’s related to tomatillos. If you’re familiar with tomatillo, it looks like a tomatillo. But it’s much smaller and it’s yellow. And it’s got—tomatillo is a tart flavor, but ground cherry has a sweeter flavor.

GRABER: When I had a ground cherry for the first time, about a decade ago, I totally freaked out in surprise and delight. They’re sweet and addictive, and I get so excited when I see them for a few weeks a year at the farmers market. But they’re expensive, and they’re not around for long. Because, like other orphan plants, they’re kind of a pain to grow.

VAN ECK: The plants are very… have this wild growth habit. They grow very large and they’re unmanageable. And also they’re called ground cherry because the fruit drops to the ground. Which you can imagine makes it very difficult for harvesting if you were, say, in a larger agricultural production setting.

TWILLEY: Funnily enough, ground cherry’s rockstar cousin, the tomato, also had many of these annoying characteristics back in the day. But over the course of time, humans bred those out.

GRABER: And then geneticists like Joyce figured out what genes in the tomato had changed over domestication to make the tomato more user-friendly. You know, the fruit grew more orderly on the vine, it didn’t drop on the ground, it was the right size.

VAN ECK: We decided to look for a plant species that was more distantly related from tomato but also was underutilized and had very little domestication or crop improvement effort. And that happened to be the ground cherry.

TWILLEY: Could Joyce and her colleagues use CRISPR to deliberately make a change in the ground cherry that had been just a lucky mutation that humans noticed and then kept breeding into the tomato?

GRABER: Take the out-of-control growth of the ground cherry. Joyce knew just what gene should in theory turn that off. When this gene is working, like in the ground cherry, plants just grow wild. But if that gene gets harmed when the CRISPR system slashes at it, then the plants should be much more compact.

TWILLEY: So Joyce built a little CRISPR set-up to target the ground cherry version of the gene that she knew turned off the wild growth in tomatoes. And she put that CRISPR system in some ground cherries. And, hey presto, her new look, CRISPRerized ground cherry was the opposite of its old, spidery, long-trailing self. The DNA that coded for that kind of unmanageable growth was gone, and so the plant now… self-prunes.

VAN ECK: Oh, it was—it was dramatic. It was a huge difference in what we were seeing. We went from plants that were, I’d say, five feet tall for the non-CRISPR, non-edited lines at maturity, to plants that were maybe two feet tall.

GRABER: Now, if plant breeders wanted to breed this type of self-pruning trait into a ground cherry the traditional way, they’d find a ground cherry plant that happened to be small and compact but maybe it didn’t taste as sweet, and they’d breed it with a sweeter one, and then grow the new plants out, then find out which offspring was both sweet and self-pruning, and they might have to do that a bunch of times.

TWILLEY: And if they were very, very, very lucky, they’d end up with a ground cherry that was everything they wanted. But they might retire first.

VAN ECK: Yeah. So it would take definitely more than 10 years to be able to do that type of work.

GRABER: But CRISPR is dramatically faster, and more targeted. It took Joyce and her colleagues only two years to get self-pruning ground cherries.

VAN ECK: So our work with the CRISPR is taking this angle where we’re using CRISPR to fast-track domestication, fast-track improvement.

GRABER: This was an amazing improvement, but it’s not enough yet. Joyce has spoken to local farmers around Cornell, and they say there’s a bunch of other changes that would help ground cherries go mainstream.

VAN ECK: We have a long wish list.

GRABER: It’s possible that for some of the items on Joyce’s wish list—things like fruit size, or whether the fruit drops on the ground before it ripens—if Joyce wants to change these, it might not be as easy as just targeting one gene. Genes often aren’t direct codes, one gene does one thing. It often takes multiple genes that work together to create something like drought-resistance or flavor.

TWILLEY: In its native bacteria, CRISPR usually goes after one thing at a time. But scientists have taken the CRISPR system and tweaked it so it can go find and slice multiple different things simultaneously. That means that Joyce could potentially design one CRISPR system that would target all the however many genes she needs to target in ground cherry to deal with its fruit drop problem.

GRABER: Or you could use CRISPR to target lots of different genes that change different traits all at the same time. This is a pretty new and super useful development— Yiping Qi has just successfully tried it in rice.

QI: We simultaneously targeted three genes and focusing on the trait which is about seeds. So we were able to enhance the number of seeds produced per plant and also how big the seed is, you know, per grain. So putting them together, sort of targeting them together, we were able to drastically enhance the yield.

TWILLEY: The main thing that makes CRISPR so useful for these kinds of edits is how precise it is. In a lot of crops, a piece of DNA that affects yield might be pretty tightly connected to, say, the DNA for a certain kind of disease resistance. In normal breeding, you can’t break that link—which means you can’t disconnect one trait from the other. But Jennifer says that CRISPR is kind of like a scalpel—it can get in there and separate even tightly connected genes.

KUZMA: With CRISPR, we can go in and we can make very precise, targeted changes at particular locations in the DNA. So it’s kind of like taking paper to pen like you would edit a book. You can go in and you can edit the letters in a word or you can change different phrases or you can edit whole paragraphs with CRISPR technology at very specific locations.

GRABER: We should say, none of these CRISPRed crops are available in stores yet, but some are pretty close. CRISPR is fast, it’s inexpensive, it’s precise, scientists love it, breeders love it. I mean, what’s not to love?

TWILLEY: I’m so glad you asked Cynthia, because I am falling head over heels for this CRISPR magic. But then, my cynical bitter side is saying—hey, there must be a downside. And my cynical bitter side will be right back to talk about that after we tell you about one more sponsor this episode.


GRABER: So—downsides. A couple of years ago, scientists were super excited about a gene-edited cow.

NEWSREEL: This is Brie. He might look like any other cow, but there’s one little thing about him that sets him apart from his breed. Brie has never grown a pair of horns. And that wasn’t a fluke of nature.

GRABER: Brie the cow wasn’t edited using CRISPR, but using a similar set of genetic scissors from bacteria. Scientists used these scissors to create a cow that wouldn’t grow any horns, so the animals couldn’t gore farmers or other animals.

TWILLEY: Normally, a cow’s horns have to be removed by hand, which some people say is painful for the animal. So this genetic edit was pretty cool. Except that it turned out that the edit was not quite as precise as the scientists had hoped.

GRABER: Two things happened. First, a bit of that foreign bacterial DNA was left in the animal—it was supposed to have been removed entirely.

TWILLEY: That’s a problem because now the hornless cow has got a little bit of alien DNA inserted in it. So rather than being one of these new school gene-edited organisms, it’s more like an old school GMO, like the fish tomato.

GRABER: And second, there was an accidental bit of DNA that also got inserted, and this one seems to have to do with antibiotic resistance. So like maybe if the animal got sick, antibiotics wouldn’t work as well. That’s pretty bad.

TWILLEY: So long story short, yes, these new gene editing techniques, including CRISPR, they are super precise, but they’re still not 100% precise. That antibiotic resistance—scientists call that kind of unwanted extra edit an “off-target effect.” Doing your edits with CRISPR should lead to way fewer off-target effects than the old-school, blast-your-gene-into-the-DNA method. But there could still be some.

GRABER: In plants, breeders and researchers like Joyce so far haven’t seen any major bad side effects from CRISPR. They are keeping an eye out, of course. And, of course, regulators are going to be asking questions about things like this before they approve any new crop for the market, right?

TWILLEY: You say “of course,” but, actually, Jennifer told us that that’s one of the things about CRISPR-edited crops. They’re not regulated like conventional GMOs.

GRABER: And this is where things get even weirder and more complicated. The Department of Agriculture, the USDA, has to approve crops grown in the field. And the way the regulations are written now, a crop is only considered genetically modified if it has foreign DNA in it. But it’s easy to use CRISPR to make a change and then get rid of it, so there’s no bacteria left.

KUZMA: And so therefore we have a couple dozen and probably more, approaching 30 to 40 now, crops that have not been regulated from a pre-market standpoint and didn’t have to undergo field trials by the United States Department of Agriculture.

TWILLEY: This is actually one of the things that scientists and start-ups love about CRISPR. Yes, they love how precise it is. But they also love the price tag. Because putting a GMO crop through field trials—that’s really, really expensive.

KUZMA: Some have estimated hundreds of millions of dollars to get a crop, a genetically engineered crop through the regulatory system. Now I don’t think it’s that high. But it is costly. At least a million, probably.

GRABER: Yes, CRISPR scientists love that regulatory loophole. But as it turns out, CRISPR can be used to insert a foreign gene, too, and it can do so a lot more precisely than genetic engineering systems did in the past. That’s something Yiping has been working on, but it’s not easy.

TWILLEY: In other words, Yiping thinks you could one day use CRISPR to put a fish gene in a tomato, and you could do it with great precision.

GRABER: But then it would be regulated the way the original fish tomato was, and, like we said, that cost a lot of money.

TWILLEY: But, for now, like Jennifer says, the USDA is not bothering itself with CRISPRed crops. Because they don’t have new DNA. But there’s a different agency in charge of approving whether that crop makes it to market as a human food. The Food and Drug Administration.

KUZMA: Now FDA does have a policy and it’s a voluntary policy—the Food and Drug Administration—to review these cops for food safety concerns.

GRABER: That voluntary policy just compares the CRISPRed food and makes sure that it’s substantially the same as the non-edited food. But again, voluntary.

TWILLEY: Jennifer says most companies seem to be going along with this voluntary check. And, in fact, to give credit where credit is due, it was the FDA that caught the problems with extra bacterial DNA in those hornless cows. The company wanted to send them out to the slaughter house to turn into hamburgers, and so the FDA took a look. They literally examined the genetic code of these new hornless cows, and they spotted the extra bits of DNA that weren’t supposed to be there, and they said, “Excuse me, we seem to have a problem here.”

GRABER: This is exactly what the FDA is looking for—these off-target effects, unexpected side-effects that might have come along with the intentional gene editing.

KUZMA: And so they do check for things like, is what you’re modifying going to cause more allergens in the food, or is it going to decrease the nutritional value of the food, or increase the toxicants in plants. Plants have a lot of toxic chemicals to ward off pests. And so whenever you make a genetic modification it can increase or decrease those toxins and the nutrients as well.

TWILLEY: So having the FDA check all that sounds like a good idea. But, Jennifer told us that what’s not happening is any ecological field testing for environmental effects—so like effects on pollinators or other plants. That kind of testing would be done by the USDA, and, like we said, they don’t screen these new crops unless they contain foreign DNA.

GRABER: This loophole seems like it could potentially be an issue—but, in a way, Jennifer says the loophole has been good for the field, because there’s been a lot more creativity. More scientists have been able to use CRISPR to see how it could help improve all sorts of crops, and not just the big money-making ones. They’re using it on orphans like ground cherries.

TWILLEY: And regionally important crops like cassava and millet that millions of people depend on in developing countries but that have never had the kind of investment that gets lavished on commodity crops like corn and wheat.

KUZMA: And you can do things that are better for the environment or better for health without having to really recoup your investment in the technology. So some people say it has a democratizing force on the technology, so that a wider variety of actors not only big industry are able to play in this space of CRISPR technology

GRABER: And because CRISPR is so fast, so inexpensive, and can target multiple regions of the genome, scientists are using it to try to make changes in response to the challenges that farmers are facing now, as the climate’s changing. They’re trying to do things like make plants more drought resistant, or capable of tolerating hotter temperatures.

QI: So I think CRISPR can sort of help us catch up climate change.

TWILLEY: This is not a super inspiring reason to love CRISPR—basically, everything is going to hell so fast the plants can’t keep up so we have to use CRISPR to help them evolve faster—but hey, that’s the boat we’re in these days.

GRABER: Another sucky thing that CRISPR might help with—nearly all the bananas that are grown commercially in the world are all the exact same variety, and they’re threatened by a banana fungus. Scientists are using CRISPR to try to help make our bananas resistant to that fungus. Again, crappy reason—can’t we just start eating different types of bananas? But CRISPR does seem to offer one potential solution, if it works.

TWILLEY: Maybe more excitingly, CRISPR can also help us move away from those kind of monocultures and that reliance on just a dozen major crops. That’s part of why Joyce is CRISPRing the ground cherry.

VAN ECK: So there’s a big emphasis right now especially on diversifying our diets. Eating more fruits and vegetables, you know. And is ground cherry going to be a huge production like tomato or corn? No, but again it does give us another option for not only fresh fruit but it can be used as dried and put in granola and cereals and jams and juices as well.

GRABER: But. But, but, but. It won’t surprise regular Gastropod listeners to know that CRISPR is not the solution to all our problems.

TWILLEY: We are not going to wake up tomorrow to a supermarket full of new and improved CRISPRized crops. For one, CRISPR works slightly differently in every different plant, and not all plants are super amenable to being CRISPRed. We’ll still need traditional breeding—CRISPR is not going to replace that.

GRABER: Plus, biology is super complicated. We haven’t sequenced the genomes of all the plants. And doing it at the level of detail you’d need for CRISPR takes a long time and is really expensive. And even if we have that, we don’t know what all the genes do. And even when we do think we know that, well, we’re often wrong. Biological systems are not like a computer code, where basically you write something and the computer responds the way you tell it to.

TWILLEY: Meanwhile, while we figure out the biology, we also need to figure out the policy side. There are a lot of things we could get right with CRISPR-edited crops that we got wrong with GMOs. Like clear and transparent labeling.

KUZMA: I think by putting these genetically engineered products on the market back in the mid-90s without people really being aware and without labeling them, I think people felt duped or tricked in a way in that, oh really? I’ve been eating these for 20 years and I don’t know?

GRABER: And so in order to change the conversation around these next-gen gene-edited foods, Jennifer thinks they should be labeled, too.

KUZMA: I mean, the way I view it is if you think this technology—which I used to be a plant bio-engineer—if you think it’s wonderful and it can do great things and you’re sure about its safety, then label it and be proud of it and show people what it can do for them. Show them how you can make tastier products or more nutritious products or healthier products or ones that are better for the environment, that use less pesticides or less fertilizer. Show them that and be proud of it and label it.

TWILLEY: Some of the scientists who work with CRISPR in crops share Jennifer’s opinion. And some are like, well, we don’t need to be labeled or regulated because this is so precise and nothing is a problem, and just leave us alone to work our magic. And to a large extent, they have a point—most CRISPRed crops seem just fine.

GRABER: But Jennifer thinks a little bit of caution and little bit more public discussion is a good thing. The plants seem fine, but they’re new—plus, Jennifer says that caution and discussion and transparency will help us all be more comfortable with using these technologies.

KUZMA: I know I tend to feel better knowing that somebody is looking out for me with consumer products, whether they be food or otherwise.

GRABER: Personally, I’m with Jennifer.

TWILLEY: It’s hard to predict how CRISPR might transform our food. Our yogurt has been CRISPERized for more than a decade and, in some ways, it seems like nothing has changed. But Dennis told us that in fact, CRISPRed bacteria are so reliable and high performing that yogurt companies don’t have to use additives to make sure they get the texture and creaminess they want. The microbes don’t need that back-up anymore, so those kinds of stabilizers and thickeners are being used less often.

GRABER: And so maybe if CRISPR can help Asian farmers produce more rice in their rice paddies, they’ll earn more money, which is great, and also maybe something else could happen—maybe they won’t have to convert more land to farmland, which could potentially be better for the environment. Dennis had no idea what was going to happen when they discovered how CRISPR worked in bacteria, and we don’t know where CRISPR is going to take us next.

TWILLEY: Cynthia, you asked at the beginning of the show whether we should be worried or excited about CRISPR in our food. And the answer is yes. Worried and excited.

GRABER: How about cautious and excited? That’s how I’m feeling.

TWILLEY: OK cautious, excited, and kind of amazed that I finally understand what all the hype is about.


GRABER: Thanks this episode to Dennis Romero and Annie Millen at DuPont.

TWILLEY: And to their former colleague Rodolphe Barrangou for originally telling me the CRISPR yogurt story back in 2014.

GRABER: Thanks also to Joyce Van Eck at the Boyce Thompson Institute, to Jennifer Kuzma at NC State, and to Yiping Qi at the University of Maryland—we have links to them and their work at gastropod.com. And I highly recommend you try a ground cherry if you’ve never had the pleasure.

TWILLEY: Finally, thanks to our fabulous former intern, Emily Pontecorvo, for finding some of the news footage we played during this episode. We miss you, Emily!

GRABER: We’ll be back in two weeks with something we’ve definitely earned this episode—a drink! But not just any drink. All I’ll say is three dots and a dash. Can you break the code?


What’s CRISPR Doing in our Food?

You've probably heard the hype: CRISPR will revolutionize biotech, cure disease, resurrect extinct species, and even create new-and-(not-so)-improved humans. But what is CRISPR—and what's it doing in our food? The first generation of genetically modified crops, or GMOs, were labelled "Frankenfoods" by critics and are banned in the European Union. Can CRISPR succeed where fish-tomatoes failed? And what's yoghurt got to do with it? Listen in this episode for the CRISPR story you haven't heard—and for a taste of our CRISPRized future.


TRANSCRIPT Running on Fumes: Strawberry’s Dirty Secret

This is a transcript of the Gastropod episode Running on Fumes: Strawberry’s Dirty Secret, first released on August 27, 2019. It is provided as a courtesy and may contain errors.

MATT CELONA: In the first year that we did pick-your-own, we tried to do it on two days, Saturday and Sunday. And so we put a barrier like thinking like, okay, people will pick this part of the bed today. And the people literally pushed the barrier over and picked the whole thing. It was crazy trying to control the crowds. And it’s like, for those few hours it’s mayhem and we call it, like, strawberry zombie time.

CYNTHIA GRABER: This is basically me in June at the farmers market. I can’t buy enough—I bring home quarts and quarts and I eat as many as I can and I make ice cream and popsicles and then I freeze whatever I haven’t devoured. I am a strawberry zombie.

NICOLA TWILLEY: This has never happened to me. Because, to be honest, I’m more of a raspberry girl. But Cynthia, I hate to break it to you—we can get strawberries basically all year round in the great state of California.

GRABER: Not just you—everyone can get California strawberries all year round. That’s where nearly all the strawberries for the entire U.S. are grown today. I have to say, I don’t love those year-round strawberries, I think they’re basically flavorless. I reserve my enthusiasm for the local ones in the summer. But this does make me wonder: How did California corner the market on strawberries?

TWILLEY: That’s the story we’re telling this episode: it’s that age-old tale of an innocent young berry that heads west to California to make its fame and fortune and loses its soul in the process. Cue violins.

GRABER: That soul it lost, it’s not just the missing flavor. It’s also the deal with the devil the strawberry had to make to become so world-famous—that is, its deep entanglement with chemicals known as soil fumigants.

TWILLEY: So what are fumigants, and how did strawberries end up in bed with them?

GRABER: Plus, what’s their impact on the environment and on human health? And can the two ever get a divorce?

TWILLEY: All that plus a sneak peek at the strawberries of the future. But first we have a couple of important news flashes. In case you’ve been living under a rock: we are having a very important birthday. That’s right, Gastropod is turning FIVE! In September!

GRABER: Five whole years! Which is actually an eternity in the podcast world. Sometimes it seems that way to us, anyway. But we are celebrating!

TWILLEY: And you are invited—we are making a special birthday episode. Also, if you happen to want to get us a birthday gift, hint hint, now is the moment to do it! We’ve got a super special prize for anyone who donates between now and the end of our birthday month—just go to gastropod.com/support.

GRABER: We’ll be offering this special birthday present for all of you, and, of course, for us, until the end of September. And if you’re a long-time Gastropod supporter already, don’t worry, we haven’t forgotten about you! We have a special present for you, too, in honor of our birthday. We love feeling the love from all of you, and we are going to give it right back!


PATRICK EDGER: So that’s actually a common misconception is that what we call the fruit is actually not the fruit. It’s a botanical organ called the receptacle. And if you ever look on the strawberry fruit itself, the little—you’ll see little studs of what we sometimes call seeds. Well, those are actually individual fruits. And the seeds are within those.

TWILLEY: This is Patrick Edger. He’s an assistant professor at Michigan State University and he studies plant genomics. He’s been on Gastropod before—he described the evolutionary war between butterflies and cabbages that gave us mustard.

GRABER: And in case Patrick’s botanical description of the strawberry caught you by surprise—and we were surprised, too—yes, he really is saying that the delicious red berry you eat? It’s not fruit. It’s the receptacle for the fruit. Basically, it’s the fleshy growth from a flower that forms to hold all the fruits.

TWILLEY: And the things you think are seeds on your delicious red receptacle? Nope, those little sesame-seed-looking dots, those are the fruits! The real seeds are hidden away inside them. I feel like my entire relationship with strawberries is built on a lie.

GRABER: Fruit or not, my zombie relationship to strawberries is mostly because those fleshy receptacles entice me with their smell.

TWILLEY: You are not the only one to have noticed this.

EDGER: So strawberry or its Latin name Fragaria was named by Linnaeus because it has a sort of striking aroma to its fruit.

GRABER: The ancient Roman poet Virgil called the strawberry ‘fragrant fruit born of the soil.’ A small variety was enjoyed more than a thousand years ago by the imperial court in Japan. Indigenous communities in what’s now Chile cultivated them for millennia before the Spanish conquest.

TWILLEY: So many strawberries, so many flavors.

EDGER: There’s one that I particularly like that tastes like a—almost like a little pineapple. It’s wonderful. It’s actually yellow in coloration. It’s very tropical tasting, very small. The fruit’s maybe the size of a pinky nail, so it’s incredibly tiny.

GRABER: That pineapple-flavored pinky-sized fruit is one of dozens of species of wild strawberries that have been around for millions of years. But the cultivated strawberry you can buy at the store? That’s super young.

STEVE KNAPP: That modern strawberry really only has 300 years of domestication history. It originated from chance hybrids from plants carried from the New World to the Old World by early explorers. And so it’s a hybrid between two wild species actually.

TWILLEY: This is Steve Knapp, he’s director of the strawberry breeding program at the University of California, Davis. He and Patrick recently collaborated on a project to decode the genome of the strawberry.

GRABER: What’s weird is that for most fruit, we have no idea when the fruit we eat today emerged. It probably took place over thousands of years, it took a lot of time and generations of mixing of different plants. But for the commercial strawberry, we know precisely where and when it was born.

EDGER: It occurred from a collection—a voyage to Virginia about, you know, 300 years ago. Wooden ships, collecting strawberry of one of the progenitor species called Fragaria virginia. It was brought back to France and then later there was a subsequent expedition where they collected the other species, Fragaria chiloensis from Chile, and then brought it back to France as well. And then, in a known greenhouse in Versailles, they accidentally hybridized. And then all of sudden they saw this massive strawberry emerge. And that really transformed the strawberry industry and what strawberry people eat.

TWILLEY: All the sudden, bingo: big conical red berries, rather than tiny little round ones.

GRABER: The new berries were hardier, too, which was a big deal. And they still tasted amazing.

TWILLEY: The British writer Samuel Butler was sufficiently moved to write “Doubtless God could have made a better berry, but doubtless God never did.”

GRABER: Samuel, you and I have something in common. And Samuel Butler could have enjoyed those heavenly berries for longer than in the past. Because the wild strawberries he’d have eaten otherwise—they were the very definition of ephemeral.

EDGER: They also have this quality that’s referred to as they melt. And so if you pick a wild strawberry, they will, like, melt in your hand. You can see them melting.

GRABER: These larger, less melty strawberries’ first home was in the northwest corner of France; the growers there supplied the markets of Paris and London. The farms were near the coast, and the region had a lovely marine environment with mild temperatures year round. Sounds like—

TWILLEY: The gorgeous coast of the gorgeous state that I am lucky enough to live in: California!

KNAPP: California is really blessed with this wonderful Mediterranean and subtropical climate mix. We also have good alluvial plains and flat areas where, you know, flowers and strawberries and lots of other crops thrive. We just have this ideal mix of temperature, the ocean cooling effect, and arable land.

GRABER: Wild strawberries might have been adapted to all sorts of environments, but this new breed of strawberry, it had finally found the perfect home. California had everything the strawberry could desire.

JULIE GUTHMAN: So the reason that California has become such an important place in the strawberry industry is it has these two kinds of natural advantages.

TWILLEY: Julie Guthman is a sociologist at UC Santa Cruz and she’s the author of the new book, Wilted.

GUTHMAN: Strawberries like sandy soils and they like temperate temperatures. And so most of the strawberries grown in California are grown very close to the coast, within three miles. People who’ve experienced summer on the Pacific coast know that summer like today, it starts foggy in the morning and warms to a nice 70s or so in the afternoon. So it’s never very hot. And so for the strawberries it’s like an eternal spring. And many other regions just don’t have those natural advantages.

TWILLEY: Blessed with these natural advantages, the California strawberry industry gets going. By the early 1900s, it’s already starting to be a serious business, although growers are still mostly only selling to the San Francisco market.

GUTHMAN: And when they first grew strawberries in California experimentally, they’d often grow them in between rows of apple trees. Strawberry farming then was still fairly small-scale, the strawberries were mixed in with other crops on the farm, and you could only get them a few weeks a year. They were a treat.

TWILLEY: So we’ve met the hero of our story: the California strawberry. But now we have to meet the villain. Its name is wilt.

GUTHMAN: So wilt refers to a problem of soil disease that comes from soil-borne fungi that get into the plants’ tissues and clog them up and disable that plant from being able to uptake water and nutrients and causes them to wilt.

GRABER: Julie’s book Wilted is, yes, largely about the meeting of heroic strawberries and the villainous wilt. The fungi is technically known as verticillium dahliae. And it’s bad for a strawberry plant.

GUTHMAN: It may still produce strawberries but it may not produce any. Often the wilt doesn’t happen till late in the season and so growers might get strawberries at the beginning of the season, and then they’ll see the wilt and they’ll get a less of a harvest.

TWILLEY: Now it’s not like wilt saves up all its evil powers to attack the strawberry. This is not personal.

GUTHMAN: It affects many, many plants. Tomatoes and potatoes and cotton and lettuce. Probably many, many others. I think there’s maybe over 150 plants are host to the pathogen.

GRABER: So wilt can kill a lot of crops. But it doesn’t sound too smart to kill off the plants you colonize.

GUTHMAN: It’s a bad evolutionary strategy for sure for a fungi to kill its host. And so you know in most settings something like verticillium is more of a parasite on its host.

TWILLEY: But in the strawberry situation, it does make sense for wilt to kill its host. Because the farmer is just going to come along and plant another strawberry plant in the exact same spot next season. There’s no penalty for killing your host.

GRABER: And so, by the 1920s, when the strawberry industry in California had started to grow, they also started seeing problems. Fields of strawberries would just all die.

TWILLEY: Farmers had no idea how to fight the wilt.

GUTHMAN: That didn’t help. For instance they used to leave strawberries in the ground for a very long time. Because strawberries will continue to produce. So if you don’t rotate those strawberries elsewhere the fungi will persist in the soil and reappear every year.

GRABER: And then on top of that, the farmers watered more heavily to try to revive their wilting plants, but verticillium actually loves damp soil. So that made it worse, too.

TWILLEY: So… maybe the strawberry is not going to make it big out west after all?

GRABER: But wait, World War 1 to the rescue.

TWILLEY: Specifically, tear gas.

GUTHMAN: And chloropicrin was tear gas. It was used to gas soldiers in World War One. When people are exposed to chloropicrin, they—their eyes tear and they want to vomit. And so what would happen is enemy troops would spray chloropicrin and soldiers would pull off their their gas masks to vomit and they’d be exposed to the full array of lethal chemicals.

GRABER: And then they died. Lovely.

TWILLEY: But, so did all the insects! Some bright spark noticed that yes chloropicrin caused crying and vomiting, but, also, there was a noticeable shortage of bugs in the areas where it was used.

GRABER: After the war, there was a lot of chloropicrin left over. So an entomologist started testing it on soil and found that, yes, it worked to kill bugs—but it also killed crop seeds, so he recommended waiting after using it before planting.

TWILLEY: Now, chloropicrin was super toxic, it smelled bad, and it made people really nauseous when they used it. But, at the time, there were a lot of scientists seeing whether weird left-over chemicals could be useful in the fields

GUTHMAN: Yeah, there was a lot of experimentation with chemicals. I mean it was such an imperative to control disease and pests. And I don’t know that there was a lot of public reaction to what the long-term effects would have been.

GRABER: Julie wrote in her book about a pineapple scientist in Hawaii who got a shipment of fifty-five gallon drums filled with chemicals, they were all waste products from Shell Oil’s petrochemical research.

TWILLEY: It was like Christmas morning. He went out, dug holes in the pineapple field every fifteen inches, poured in these random liquids, and waited to see what died.

GRABER: And a lot of creatures did. Dow Chemical heard how impressive those field trials were, they figured out what in the chemicals was doing the killing, and today that chemical is still in use in agricultural fields to kill tiny worms.

TWILLEY: But not strawberry fields. For strawberries, the magic bullet was chloropicrin—that’s the tear gas—but specifically chloropicrin used *in combination* with a chemical called methyl bromide

GRABER: Methyl bromide was first developed as a flame retardant, but then quickly scientists figured out that it could wipe out insects, too. In fact it was used in the Second World War to delouse soldiers.

GUTHMAN: So those two chemicals used in combination were the ones that the university scientists came upon in the 1950s, together they worked really well to control verticillium wilt.

TWILLEY: Like the pineapple scientist, California strawberry farmers injected this combination into their soil. Both chemicals were toxic, but methyl bromide was better at moving through soil, and chloropicrin had a noticeable smell, which was a helpful warning sign. And together—they fumigated the soil.

GUTHMAN: Well they, you know—sometimes they call it disinfestation, sometimes they call it sterilization. It kills a lot.

GRABER: Today we call those particular chemicals fumigants. They fumigate the soil. As Julie said, they kill nearly everything in their path. Including wilt.

GUTHMAN: Starting in the 1950s, growers started to fumigate instead of doing other techniques to control wilt. And by the 1960s, fumigation was a widely used practice.

TWILLEY: It wasn’t just that these fumigants stopped the strawberries from dying from wilt. Turned out injecting the soil with poison had other benefits.

GUTHMAN: Well, it had a tremendous effect on yield. I mean, after growers started using these chemicals combined—yield increased 20 or 30-fold. Huge increases. And part of it is like they don’t even know what was working about it. I mean, certainly they were losing less fruit to just the wilt, but they believed that there was something in the mix of these chemicals that was having an effect way beyond controlling wilt. That was giving it some sort of boost.

GRABER: Unsurprisingly, nearly all strawberry farmers started to fumigate. You kind of had to—banks wouldn’t even lend to farmers who didn’t. Because it was kind of like an insurance policy; you basically knew you’d likely have a successful crop if you fumigated.

GUTHMAN: And so growers who didn’t fumigate just wouldn’t stay in business very long. I mean there is a cost to fumigation and today it’s very expensive but pretty much everybody adopted it.

TWILLEY: So it’s the 1950s, and our hero the strawberry has had to get in bed with a couple of shady characters. But it seems like nothing can stop it now!

GUTHMAN: So fumigation did solve a whole lot of problems for growers and allow them to focus on a lot of other things including breeding for other qualities. They didn’t have to breed for disease resistance anymore. So it became all about breeding for yield and ship-ability. You know, in other words, a berry that wouldn’t rot.

GRABER: And then really quickly in the 1950s, after breeders turned away from wilt worry, they had a big breakthrough. They were interbreeding cultivated strawberries with a wild plant and they brought in a useful gene—

KNAPP: That had a really profound effect on changes in production, and it’s called day neutrality, but it’s a gene that allows the plant to flower under long days.

TWILLEY: This is Steve again, our strawberry breeder. And for the strawberry, this day neutrality gene is like winning the Triple Crown. Now you’ve got a strawberry that can grow year round, you’re breeding it to be more and more productive and long-lasting; meanwhile, your fumigants are taking out wilt and also boosting production. And, just as an added bonus, it’s the 1960s 1950s and pretty much everyone in America now has a shiny new refrigerator in their kitchen. Strawberries for the win.

GRABER: And so strawberry farmers bought new land. They planted more and more. They planted the strawberries year-round, no need to rotate crops because the strawberries never died.

GUTHMAN: And it created this surplus of fruit. I mean lots and lots of fruit. And so the California Strawberry Commission, which is the main industry group that supports research and marketing for strawberries, has had to do a lot to market strawberries because there’s so many grown. And so they’ve done all sorts of marketing campaigns. They work with retailers to feature strawberries in the front. They’ve done advertisements to encourage you know to tell people that strawberries are important or healthy or good for you or your kids’ll love them or that they’re antioxidant. And so there’s been a lot of work behind the scenes to get consumers wanting those strawberries. Productivity came first and then they had to figure out how to market them.

GRABER: And it worked. Strawberries are the most popular berry in America. Kids seem to love them. They’re in all sorts of processed food snacks. They’re everywhere.

TWILLEY: The strawberry came out west to make its fortune, and it has. Is that the end? Are we done, Cynthia?

GRABER: Well, Nicky, you and I have been making Gastropod episodes for five years now, and we both know—and you listeners know—that the story’s never quite so pretty. Because all those fumigants that all the strawberry farmers use to clear out the soil before planting? Well, maybe it won’t shock you to hear that they have some pretty serious downsides.

TWILLEY: Downsides! You know you want to hear all about downsides. And, of course, how our hero the strawberry might yet be able to overcome them.


TWILLEY: There are a lot of rules and regulations around fumigation that are designed to make it totally safe. For starters, it’s not like these chemicals are just sprayed on the field.

GUTHMAN: It’s a below-ground treatment and growers are no longer allowed to do it themselves. They hire out companies. There’s one company that does about 95 percent of the fumigation in California. The fumigation company has a rig and everybody suits up in this you know hazard protection equipment. And they go through the field and inject it into the soil and then cover it with plastic. And no one’s allowed to—supposedly allowed to go near that for several days after fumigation.

GRABER: Sometimes of course the plastic tears, and people do get exposed to the chemicals. It’s also an issue with communities that live near the farms.

GUTHMAN: There’s also people who after the fumigation takes place, there’s people who go round and shovel and they often do not wear protective equipment. So there’s all sorts of potential for exposure.

GRABER: Chloropicrin was, of course, tear gas, and it causes headaches and nausea and dizziness. If you’re exposed over the long-term, it can cause lung damage, and maybe cancer.

TWILLEY: Chronic exposure to methyl bromide is also not a good idea. High doses will kill you, but constant, low-level exposure damages your nervous system, it damages your liver, kidneys, and lungs. It’s carcinogenic. And scientists have found that pregnant women who live within 3 miles of fumigated fields have smaller babies, with lower birth weights and smaller head circumferences.

GRABER: Of course the protective gear and the plastic cover and the waiting time before planting, that’s all supposed to protect farm workers and people who live near strawberry fields. But Julie says that doesn’t always work.

GUTHMAN: This is a super contested thing. The strawberry industry thinks these accidents are unusual and hardly happen anymore. And if you talk to public health or farmworker communities they’ll tell you that it happens all the time and they don’t get reported in part because people don’t want to be deported or whatever.

TWILLEY: To be clear, what’s contested is how common exposure to fumigants is, not whether that exposure is a bad thing.

GUTHMAN: Most agree right now that they’re pretty toxic. The question is is whether the existing mitigation measures are effective enough at preventing toxicity to get to humans.

GUTHMAN: And again the degree to which these fumigants affect the plant or affect the pathogen is something that’s very little known about.

TWILLEY: Obviously, when you kill everything in the soil, you’re killing good things as well as the wilt. And Julie says that may well have led to the emergence of new strawberry diseases.

GUTHMAN: Fumigation pretty much controlled verticillium wilt. But in the past 15 or so years there’s been new pathogens that have emerged in the strawberry fields. But it’s also possible that those pathogens were there all along and appeared because of the changes that fumigation and the whole system did to the relationships between the plants and soils and diseases.

GRABER: And these are not the only problems that fumigants cause. Back in the 1980s, everyone was all worried about the hole in the ozone layer that was letting in more and more UV light that would kill plants and give everyone skin cancer. If you were around then, you might have thought your fridge and your aerosol hairspray were the biggest culprits—

TWILLEY: Which they were. But strawberries were to blame too.

GRABER: Specifically, methyl bromide. And so its use was phased out as part of the Montreal Protocol that was signed in 1987.

TWILLEY: At the time, there were other industries that also used methyl bromide. But they all had to figure out alternatives. They were given until 2005 to stop using it.

GUTHMAN: And the strawberry industry kept on lobbying the U.S. government to extend that deadline and they got what are called critical use exemptions. They said like we don’t have a viable alternative. Without methyl bromide the industry will die. And again that was the U.S. government really on behalf of the strawberry industry. They were the main group lobbying.

GRABER: But eventually even strawberry farmers had to give up their precious methyl bromide. The last year it was used was 2015.

GUTHMAN: There was another chemical that was developed to replace methyl bromide called methyl iodide. And that was super toxic, a neurotoxin. Probably causing thyroid cancer. It’s used to induce cancer in laboratory rats. It had all sorts of health effects related to it. And it was actually withdrawn from the market after a long activist battle and a lawsuit.

TWILLEY: So methyl bromide was finally gone, and there was no alternative. The strawberry industry predicted doom, gloom, and disaster. They said production would fall off a cliff.

GRABER: But it didn’t. Honestly, it’s mostly because strawberry farmers still use fumigants. They just use chloropicrin without its partner methyl bromide. It doesn’t spread in the soil quite as easily, but it still works.

TWILLEY: Basically, strawberry growers are hooked. They can’t grow on the same plot of land year after year without a fumigant. Which means they can’t grow in California without a fumigant.

GUTHMAN: I mean the cost of strawberry, of growing an acre of strawberries these days is at least $70,000. It’s probably more because labor costs have gotten really high for growers. And so to make a profit there, that means they’re making more than seventy thousand dollars an acre, which is extraordinary, compared to like something like rice which might be like fifteen hundred dollars an acre per year. So that’s a huge investment but the land is priced with the expectation that growers are going to grow this very high value crop.

GRABER: And so most California strawberry growers are still locked into this fumigant cycle, just so they can grow enough to afford the land they’re growing on.

TWILLEY: At this point, you might be starting to get a little worried. Like, oh my God, have I been eating tear gas along with my California strawberries? But researchers have tested and they have found that residues from fumigants don’t show up on the final fruit. So you are not exposed to fumigants, just the farmworkers and communities.

GRABER: Which is definitely already a reason to buy organic. But And there are plenty of other residues on conventionally grown strawberries. The Environmental Working Group lists the strawberry at number one of the dirty dozen pesticide-laden foods.

GUTHMAN: Oh, strawberries use all sorts of inputs. Fumigation’s just one of them. They’re one of the most chemical intensive plants that are—fruits or vegetables that are grown. They use all sorts of anti-fungals, they use miticides, because they have problems with spider mites. They use all sorts of inputs.

TWILLEY: In response to being named and shamed, over the past few years, the organic strawberry industry has grown. Even big industry leaders like Driscoll’s are converting more of their production to organic and not using fumigants in those fields.

GRABER: Frankly, though, I think even those organic Driscoll’s are pretty bland, since they’ve been bred to be stored and shipped long distances. As you all now know, I buy my strawberries in the summer from local farms that grow incredibly delicious, super aromatic strawberries. One of my favorite farms that grows strawberries is Mass Audubon’s Drumlin Farm. We visited with the head farmer Matt Celona.

CELONA: Right. So we are standing in our strawberry patch and we’re looking at eight thousand plants.

TWILLEY: There’s not fruit yet—it’s just like a carpet of green plants.

CELONA: Generally like the smell comes late in the season, like late June early July, and that’s when the berries are just ripening so fast and you have like this incredible sugary aroma. Smells like jelly, I suppose.

TWILLEY: Matt said that around when the fruit starts coming in, they use straw to keep weeds down. And they water the baby strawberry plants when they first go in the soil and that’s it. No sprays, no more irrigation, no nothing.

CELONA: We’d like to say like, hey, we we think the organic standard is kind of like a minimum standard and for us sort of unacceptably low. Like we want to be known for doing things beyond what’s required by the organic standard.

GRABER: And Matt said they have no problems with strawberry diseases. No issues with wilt. And lots of happy customers.

TWILLEY: But those baby strawberries? Matt gets them from a nursery. And that’s a whole different scene.

GRABER: Matt was shocked to hear about conditions in the nursery, and so was plant geneticist Patrick Edger, and we were too. But before we tell you about how those strawberry baby plants are grown, first we have one more sponsor to tell you about.


TWILLEY: Here’s the thing. Strawberries aren’t grown from seed—there’s too much natural variation. They’re cloned from runners—just pieces of the strawberry vine. And these runners are grown into baby plants at special strawberry nurseries.

GRABER: And those nurseries need totally clean stock for farmers in the U.S. and even in other countries. And so they managed to convince the powers that be that they should have what’s called a critical use exemption for methyl bromide.

GUTHMAN: It’s still allowed in the nurseries. I mean, I’ve talked to people New Zealand who use California varieties. And so because they haven’t found something that reliably keeps these plants disease free—and I think they have to, like, there can’t be any more than 5 percent of the plant can have disease or it becomes un-shippable.

TWILLEY: So this fumigant that is banned in the fields—every year, the strawberry nurseries apply for an exemption and every year they get one, and no one—even people who know a lot about strawberries like plant scientist Patrick Edger—no-one knows this.

EDGER: So actually that exemption is totally new to me. You know something I don’t know. Yeah. So—so nurseries that are propagating can use it?

GRABER: Yeah. It’s nearly impossible to buy starters from nurseries that don’t use methyl bromide.

EDGER: Huh. In glass houses or in the field?

TWILLEY: In the field.

EDGER: Huh. Yeah that’s totally new to me.

GRABER: So Patrick was shocked, and Matt was shocked, too. He didn’t even know that strawberry farmers in California use fumigants, because his farm operates so entirely outside that monoculture culture. So the idea that nurseries might use methyl bromide? Not on his radar.

CELONA: No, because I don’t know about this fumigant thing that you’re talking about. So yeah, it never crossed my mind. Wow. So, yeah, good to know.

TWILLEY: Like we said, Drumlin Farm holds itself to a higher standard even than organic.

GRABER: Matt buys his baby strawberries from a nursery nearby. He didn’t know how they grew those plants, as I said, he didn’t even know that anyone would ever fumigate strawberry fields. But I emailed that nursery, and, yes, they use methyl bromide.

TWILLEY: Even the best intentioned strawberry farmers don’t really have much of an option here. Almost all baby strawberry plants are grown using methyl bromide. In New England, according to industry sources, there are no commercial nurseries growing baby strawberries without fumigants. It’s like this dirty secret.

GRABER: But there are solutions that could wean the strawberry industry off fumigants—strawberry farmers who use chloropicrin, and strawberry nurseries who are using methyl bromide, too.

TWILLEY: In an ideal world, the strawberry industry would quit fumigants. Right?

KNAPP: Could I be un-courageous? Could I not answer that?

GRABER: Because Steve Knapp is a strawberry breeder who works with the entire strawberry industry in the state of California, organic and conventional, he really did not want to answer that question.

KNAPP:You’re just not going to let me be uncourageous, are you?

TWILLEY: Sorry Steve!

KNAPP: You know, I mean, I have deep personal feelings about our planet, right? And there are things I would like to see happen. But I really I also understand the challenges that people have to produce food. It’s you know—my view is hopefully my contribution to the world here will be to make that less necessary.

TWILLEY: Conventional strawberry growers love fumigants. So Steve’s caution is completely understandable—Patrick was the same way. But for farmworkers sake and for the environment—and honestly, maybe for the future of the strawberry itself—the industry *needs* to wean itself off them. And there are some ways it could start doing that.

GUTHMAN: One method that works is is very agro-ecological, like where you rotate strawberries with other crops or with compost. And/or with mustard seed and broccoli. Broccoli has mild fumigation properties. But in those integrated systems strawberries are a minor crop and you can only put strawberries in the ground like every three or four years because you’re using those other crops—you’re using fallows or or compost or cover crops or brassicas to fend off the pathogens. So that works but it doesn’t work—you can’t grow as many strawberries and you certainly can’t grow in the monocultures that we see in California.

GRABER: This integrated system is how Matt farms at Drumlin. And he has no wilt problems. But part of why he can afford to do that is because even though the farm is on pretty valuable land close to Boston, that farmland can never be sold to a developer. But strawberry farmland in California is incredibly valuable coastal property. And strawberries bring in a lot more money than broccoli does.

TWILLEY: In Europe, most strawberries are grown without fumigants—but also without soil.

GUTHMAN: In Europe, they grow a lot in greenhouses. And that’s certainly one of the directions the strawberry industry is experimenting with. If not full greenhouses than what they’re calling field level hydroponics, where they are growing strawberries in trays filled with soilless substrate. So rather than using soil which is is the medium of the disease, they use coconut coir or peat moss.

TWILLEY: Of course, in Europe, these Dutch greenhouse-grown varieties are also infamous for tasting of precisely nothing.

GRABER: Plus, California growers aren’t interested in soil-free greenhouses.

GUTHMAN: It’s super expensive. It’s a lot of infrastructure to use waist-high trays. They haven’t yet found varietals that really works well in those systems in California because so many of these cultivars have been bred to be in fields.

TWILLEY: And remember, the only reason the strawberry moved West is because of California’s natural charms.

GUTHMAN: But individual growers have nothing to gain by or little to gain by this because their biggest advantage is again the sandy soil and the climate. And once you move toward soilless systems and particularly if you move toward indoor growing, what’s the advantage of growing on this very expensive land in California? They could move these berries closer to urban markets.

TWILLEY: In other words, if you’re going to grow strawberries for New Yorkers in a greenhouse, that greenhouse may as well be in New Jersey.

GRABER: Farmers could use a non-chemical type of soil fumigant—there are a number of different techniques. One is called steam disinfestation, which is what it sounds like.

GUTHMAN: So rather than using a chemical, disinfesting in the field with steam injection. Which works OK. It works well on weeds but it’s super expensive and time consuming. There’s also a technique that’s been—that a lot of organic growers are using called anaerobic soil disinfestation where you’re mixing in a carbon source like molasses or rice bran into the fields and then flooding them with water and covering them with plastic and that’s kind of drowning out the pathogen, creating anaerobic conditions so it can’t replicate.

DAN NELSON: And we found that to be working very well, in particular in the nurseries where the temperatures are high. The efficacy of that treatment works really well.

TWILLEY: That last voice, that’s Dan Nelson. He is one of the co-founders of the only nursery that supplies baby strawberries that haven’t been grown using chemical fumigants. Driscoll’s—that’s the biggest player in the strawberry industry— they recently began to supply some of their growers with organic baby strawberries. But for non-Driscoll growers, Dan’s company, Innovative Organic Nursery, that’s their only option to avoid baby plants grown with methyl bromide.

NELSON: There’s a lot of other techniques that we’ve explored. we’ve got cover crops that we’re playing with. And we’re exploring almost anything that’s available to us. You know, we’ve spent the last four years effectively testing all of the options out there

GRABER: Dan’s baby strawberry plants so far are, unsurprisingly, more expensive than the methyl bromide fumigated ones. And Dan has to actually work even harder to have disease-free baby strawberries because he knows organic ones are an unknown risk for farmers.

NELSON: You know, essentially we’ve got to make sure that we don’t deliver something that is that is problematic for the growers. So yes, there are options but none of them are—have been really scaled up and a lot of them have significant disadvantages, not least of which is cost.

TWILLEY: In the meantime, there’s another path our strawberry hero could take. After all, we have bred strawberries that are bigger and last longer and are more prolific and bear fruit all year round. Why not breed strawberries that resist disease?

KNAPP: First of all, the strawberry is a fascinating species. It’s called an octoploid. So it has four different plant genomes that came together to make what we call the modern strawberry everybody’s familiar with.

GRABER: Fascinating, sure, but those four different plant genomes, or eight different sets of chromosomes, it means that breeding new strawberries is even harder than for other species that have fewer chromosomes. There’s so much genetic variability, the new breeds could kind of go anywhere. It’s hard for Steve to find the trait he wants and keep it in his new strawberry plant.

TWILLEY: We humans have just two sets of chromosomes in our genome that we inherit from our parents— one from each. In scientific terms, we’re diploids. But plants tend to be hoarders and they hold on to extra genomes when they interbreed. Still, eight sets of chromosomes is a lot. And that’s why it’s only just this year that scientists managed to publish the strawberry genome. Patrick and Steve and a couple of colleagues, specifically

GRABER: To assemble the octoploid strawberry genome, Patrick and Steve had to develop new tools to figure out how to put together genetic code for a plant that has eight sets of chromosomes. They didn’t publish the very first example of an octoploid—another team did that with the sugar cane genome earlier in the year.

EDGER: That was, you know, it’s also an octoploid. But really prior to that people really stuck with diploid organisms because how difficult it is. To even assemble something that only has four copies or a tetraploid was very, very difficult. And so for us to go on a mission to try to put together an octoploid, really, and develop tools to allow us to do this, was really pushing boundaries.

TWILLEY: And it took them a lot longer than usual. Assembling the genome of a diploid plant—that takes Patrick a couple of days, maybe three. Then maybe another month or so to make sure it’s all in the right order.

EDGER: The octoploid strawberry genome took us about two and a half years.

GRABER: It might have taken an extra long time, but it worked! They were able to assemble the strawberry genome. Which will help with breeding the strawberry of the future.

KNAPP: You could think of the genome as the foundation of a house. Without the foundation we’re not going to get the walls and the roof and the windows. And that the genome is is like a roadmap. If we don’t have that we can’t locate where a particular gene is. But once we know that it provides us with a strategic way to use DNA barcodes.

TWILLEY: Steve used to have to make crosses based on what he knew about the strawberry parent plants traits, and then he’d just have to wait and see. Now, using the genome he and Patrick assembled, he can predict which crosses will give him the qualities he’s looking for, and then test the baby plants right away to see if he’s right.

GRABER: And this is a really big deal to a really big business.

EDGER: For breeding programs, strawberry is a high-dollar crop to the U.S., worth about between somewhere between three to four billion dollars every year to the U.S. economy. And there weren’t really any tools available to guide breeding programs, to make strawberry bigger or better or more aromatic or higher disease resistance. So there were really no tools available as there are for soybean and corn and so on.

GRABER: But now that they have this tool, Patrick and Steve can use this information to breed new varieties that meet what growers need today—and, now that fumigants are being phased out, growers want plants that are resistant to diseases.

EDGER: Yeah. Oh yeah. We found hundreds of genes that are key candidates for disease resistance against a number of really important pathogens.

KNAPP: But you can imagine if you if you put the sort of the Venn diagram of all it, took all of it together, you know—be high yield, complete resistance to all pathogens. Wonderful flavor every month of the year. And so of course those are the ideals we’re shooting for.

TWILLEY: But, in strawberry plants as in life, turns out you probably can’t actually have it all.

EDGER: Of course, the plants don’t have infinite amount of resources. Some metabolic resources are now going to have to be devoted to defending themselves against some pathogens. And so there’s 100 percent going to be a trade off between yield, fruit quality, and disease resistance that people didn’t have to worry about before.

GRABER: It takes energy—metabolic resources, as Patrick says—for the strawberry to defend itself. And that metabolic resource has to be diverted away from something else. Like maybe growing bigger.

EDGER: Maybe there is a slight size—decrease in the fruit size but the aroma and the taste is going to be good—is going to be improved. But ultimately that I think will then have to be decided by consumers. But personally as a consumer myself I would be OK with a fruit that’s maybe 5 percent smaller if it’s more aromatic.

TWILLEY: Or if doesn’t require treatment with toxic chemicals.

GRABER: Yep, me too.

TWILLEY: Patrick has gone on to sequence the genomes of a bunch of wild strawberries. He’s found disease resistance genes in them that have been lost from the commercial variety we all eat.

EDGER: It’s going take us maybe a few years to be able to stack all that resistance to create new cultivars. But I’m confident that it could be done without soil fumigants

GRABER: And Patrick’s not just interested in resistance. He thinks that growers could breed a variety of strawberries, kind of like how you can buy apples that tastes pretty dramatically different from one another. Some are good for pies, some are good to snack on, some are better for applesauce…

EDGER: And of course it’d be nice, yeah, to have some diversity, right? Where we can have really a spectrum of different strawberries with different attributes. Some that maybe pair nicer in salads or some that may pair nicer in desserts or in cakes and so on. Or to eat plainly. Right? So I certainly envision a future where that’s possible.

TWILLEY: Of course, you’re not going to see all these new strawberries in the store next summer— even with the genome it still takes years to breed a winner and then grow up enough plants to introduce a new variety. But Steve and Patrick are definitely enjoying this next step in the strawberry’s journey.

EDGER: So you know it’s—so the greenhouses and particularly growth chambers where—these are highly climate controlled places where we grow strawberries. They’re sealed from the environment. Right. But as soon as we open them, like, there’s a blast of the most lovely—I mean, it’s exciting. I look forward to opening a growth chamber and getting blasted with the smell of strawberries. I look forward to that one or two times a day where I go and just check on all my plants and it’s really—it’s just really nice.

GRABER: Steve isn’t just studying strawberry genomes, like Patrick is, he’s breeding new varieties. So he actually has to eat them. A lot of them.

KNAPP:And I just eat them fresh. I just eat them fresh. I don’t do anything with them. I do make one Italian dessert with them, yeah, with sort of Madeira and crème fraîche. But, anyway, that’s the only way I ever doctor em up.


TWILLEY: If you haven’t started drooling yet, I don’t know what’s wrong with you. Even I am and, like I said, I’m really more of a raspberry girl. But I’m going to try Steve’s recipe—and you can too—he shared it with us so it’s on our website at gastropod.com.

GRABER: You might be wondering where this whole story leaves you in terms of eating strawberries. I totally love them, and I do think you should enjoy your strawberries! But I’d recommend you get them in season as much as possible and as close to you as possible. First of all, they’ll taste a lot better. Second of all, you can find out how they’re grown and try to buy from someone who grows them on an integrated farm, like Drumlin. Organic practices are definitely the way to go with strawberries.

TWILLEY: And if you really want strawberries all year round, Driscoll’s is starting to use organic baby strawberries too. But this is really a chance to talk to your farmer and ask them about their nursery. Organic baby strawberries are available from Innovative Organic Nurseries, and it’s not a bad idea to put pressure on other nurseries to clean up their act.

GRABER: Thanks so much this episode to Steve Knapp, Patrick Edger, Julie Guthman, Matt Celona, and Dan Nelson. We have links to their research and companies and books on our website, gastropod.com.

TWILLEY: There’s another reason to go to gastropod dot com and that is to get in on our awesome birthday gift exchange. You support us at any level before the end of September, our birthday month, and we give you a super special prize! If you prefer Patreon, we’re at patreon.com/gastropod.

GRABER: And we haven’t forgotten about those of you who have been long-time supporters of the show, you’ll be hearing from us in honor of our birthday, too! As we say frequently, we are just a two-person team here at Gastropod, and we could not do what we do without all of you!

TWILLEY: And guess what, because we just love to party, our next episode is also going to be a celebration! This one takes us south of the border. Any guesses?


Potatoes in Space!

Today, a half century after Neil Armstrong took one small step onto the surface of the Moon, there are still just three humans living in space—the crew of the International Space Station. But, after decades of talk, both government agencies and entrepreneurs are now drawing up more concrete plans to return to the Moon, and even travel onward to Mars. Getting there is one thing, but if we plan to set up colonies, we'll have to figure out how to feed ourselves. Will Earth crops grow in space—and, if so, will they taste different? Will we be sipping spirulina smoothies and crunching on chlorella cookies, as scientists imagined in the 1960s, or preparing potatoes six thousand different ways, like Matt Damon in The Martian? Listen in this episode for the stories about how and what we might be farming, once we get to Mars.


TRANSCRIPT Ripe for Global Domination: The Story of the Avocado

This is a transcript of the Gastropod episode Ripe for Global Domination: The Story of the Avocado, first released on May 8, 2018. It is provided as a courtesy and may contain errors.

NICOLA TWILLEY: Alright, I’m in my kitchen Cynthia, and I feel as though it’s time for some lunch.

CYNTHIA GRABER: I am thinking the same thing, and I have a really lovely ripe avocado here on the counter.

TWILLEY: I do too! I do too!

GRABER: Perfect! You might even think we planned this.

GRABER: Oh come on, don’t tell me we’re out of bread, that would be really bad.

TWILLEY: There’s no avocado toast without the toast.

GRABER: Oh here we go. God. Okay, I’ve got bread. I’m just cutting it into thin slices. The bread is ready, I’m just kind of laying out the thin slices of avocado on the toast. Okay, little mashing on the bread here.

TWILLEY: Yeah so I am so freaking bougie that I am going to put a few little pink slivers of pickled radish on mine.

GRABER: You have pink pickled radish ready for yours?

TWILLEY: Cynthia, I’m living that healthy southern California lifestyle.

GRABER: Okay, I’m sprinkling some beautiful salt on top.

TWILLEY: Oh my God, this so pretty. The pink on the green? I feel like I could literally invite Gwyneth Paltrow round to lunch.

TWILLEY: Hi Gwyneth, are your ears burning? We’re talking about you.

GRABER: No, don’t worry, we are not going to spend this episode talking about Gwyneth Paltrow. We are, though, going to be talking about an incredibly delicious fruit—yes, avocado is a fruit—and how it became the symbol of an aspirational lifestyle.

TWILLEY: We are Gastropod, the podcast that looks at food through the lens of science and history. I am Nicola Twilley.

GRABER: And I’m Cynthia Graber. So, this avocado toast thing, how in the world did it become a thing?

TWILLEY: More importantly, how did a fruit that is named after male genitalia become the poster child of the North American Free Trade Agreement and the next big thing in China?



MARY LU ARPAIA: It’s a New World fruit. It’s native to Mexico and Central America.

TWILLEY: That’s Mary Lu Arpaia. She’s head of the avocado breeding program at UC Riverside, near me in sunny Southern California.

GRABER: Nobody is sure exactly where the avocado first came from, but the oldest evidence we have that people were eating avocados comes from settlements from 10,000 years ago in Puebla, in Central Mexico.

TWILLEY: And again, no one is exactly sure where and when the avocado was domesticated—it might have happened more than once. But it was probably at least 7,000 years ago. The oldest known culture in the Americas, the Caral civilization of Peru—archaeologists have found evidence that they likely ate domesticated avocados, more than 3000 years ago.

GRABER: The Caral don’t seem to have been eating corn or other grains, and the same is true for another early culture called the Mokaya in what’s now Mexico and Guatemala. And so avocado may have played a really important role in their diets as a major staple.

TWILLEY: And we know the Maya valued avocados—the symbol they used for the 14th month of the year in their calendar was an avocado.

BROOK LARMER: When the Spanish conquistadors came to Latin America back in the 16th century, they encountered this fruit that they had never seen before that had this Aztec name ahuacatl, which means testicle actually, in the old ancient Nahuatl language.

GRABER: Brook Larmer is the “On Money” columnist for The New York Times Magazine and wrote a recent story on avocados. The Aztecs called these strange bumpy fruits testicles because they hung low, often in groups of two.

TWILLEY: And they look kind of testically in shape. I mean, I can see testicles in anything, but still.

LARMER: But the Spanish conquistadors took that name and made it into aguacate, from which our avocado has now derived in English.

TWILLEY: The conquistadors were big avocado fans, right away. The first written description of the avocado comes in 1519, from a Spanish guy called Martin Fernandez de Enciso. He described it as quote “an orange, and when it is ready for eating it turns yellowish; that which it contains is like butter and is of marvelous flavor, so good and pleasing to the palate that it is a marvelous thing.”

GRABER: Other conquistadors sang the praise of avocados as well. They likened them to figs. They said that avocados are healthy fruit for sick people, and when eaten with sugar, is like a preserve. They also said that avocados are like pears, but better.

TWILLEY: From the Spanish records we can get an idea of how indigenous Mesoamericans were using the avocado. They documented instances when it was used to pay nobility as a tribute, but they also wrote that it was for sale in the open air markets of Tenochtitlan. And apparently pigs used to gorge on the ripe fruit when it fell from the trees. Their meat was said to have a particularly excellent flavor.

GRABER: So it’s no surprise that the Spanish quickly adopted the avocado as a favorite fruit and eventually distributed it to other Spanish colonies, all around the world, where they started to grow it, too. But the avocado didn’t become a major commercial crop until recently.

ARPAIA: Even though it was grown as a door yard crop tree throughout Central America and valued for thousands of years, there was no intensive agriculture production of avocados actually until the industry in California and to some extent an industry in Florida started just about 100 years ago.

TWILLEY: What this means is that folks like Mary Lu, they’ve still got a lot to learn about the avocado’s evolution and its different varieties and its botany in general compared to more established crops like wheat. What we do know is that the avocado really old, in flowering plant terms.

ARPAIA: It’s a member of the laurel family. This is a very, very ancient part of the angiosperms.

GRABER: So ancient in fact that you have to imagine back millions of years ago, to a time when huge ground sloths the size of giraffes and mammoths stomped around avocado trees. These are the types of animals that could swallow a pit that big and then poop it out. These mega-sized animals went extinct about 13,000 years ago, but rodents picked up the avocado reproduction baton. They gnaw on avocado flesh and leave the seed to grow.

TWILLEY: Not the avocado’s target audience, but hey, it works.

GRABER: So for thousands of years, these ancient backyard angiosperms, they came in all sorts of varieties, and sizes.

TWILLEY: But not here in California.

ARPAIA: Over time we’ve gone to the point where now here in California we’re 95 percent Hass.

TWILLEY: Hass is the name of an avocado variety—really, the avocado variety that you see in stores today.

ARPAIA: Hass was a chance seedling that was actually found in La Habra Heights.

TWILLEY: La Habra Heights is a neighborhood in southeast LA, just a few miles down the road from me.

GRABER: And guess who’s behind this chance seedling?

TWILLEY: Oh my God, it is none other than our old friend, the globe trotting food explorer David Fairchild.

DAN STONE: Fairchild picks up what he sees as the greatest avocado in Chile.

GRABER: In case you don’t remember, our most recent episode was all about Dan Stone’s book called The Food Explorer. And this is Dan, describing another one of Fairchild’s adventures.

STONE: He’s visiting Chile in 1897, and he explores and he finds this great variety. It’s got a thick skin, it’s got creamy flesh. It’s not stringy at all. And he collects a thousand seeds and sends them back to Washington in hopes that at least a few will survive. A few do. And they are received in Washington, they are propagated. They are sent out to research stations in southern California toward the coast, around Fallbrook area and greater Los Angeles.

TWILLEY: There were already some avocados in California. They were brought here in the 1850s by settlers from Nicaragua. But Fairchild’s shipment of a whole bunch of new varieties got people excited about avocados again.

STONE: And people start experimenting with avocados. Farmers start growing them and scientists start breeding their seeds and seeing how they could improve them. Amateurs get into it too. In fact one of them is a postal worker, a letter carrier and in his spare time he just grows avocados in his backyard and one day one sprouts even better.

ARPAIA: It was the seed that was planted in the mid 1920s and the grower who actually was a postal worker kept trying to top-on the tree to the variety that was the dominant variety of the day. The graft kept failing. Then he finally gave up for different reasons. And then all of a sudden he realized he actually had something of value.

STONE: It’s straighter, its fruit comes faster, its skin is even thicker, its flesh is even creamier and greener. And so he decides to patent it and his name was Rudolf Hass.

TWILLEY: The mother Hass tree—it was actually still alive and growing in La Habra Heights. Apparently it got to an astonishing 65 feet tall. When I read this, I got so excited I was about to jump in the car and visit it, but then I read some more, and it died in 2002, from the dreaded root rot. There’s a plaque there now, instead, and the mother tree wood is still preserved at a nursery in Ventura.

GRABER: But even though the mother Hass tree has become so venerated that there’s a plaque for it, back when Hass avocados were new, this variety wasn’t an immediate hit.

ARPAIA: And if you read some of the older literature though, the thing that it had going against it was the fact that it turned black. There was a very nice article written in the mid 1940s where they’re complaining about well, you know the Hass is a great tree. It’s a great fruit. But my God, it’s black, not green! Because the dominant variety in the 40s up through the 70s was a Fuerte, which was a green variety. So it just shows how things have changed.

GRABER: So the black color freaked out consumers. But even though it took a few decades, both growers and eaters did eventually get used to it. Because this brand new Hass avocado had a lot going for it.

ARPAIA: Well I can go—I can wax on forever on that one.

TWILLEY: Let’s wax. First of all, in California, the Hass avocado ripens at a very convenient time.

GRABER: Farmers can harvest the Hass in March through June, after the Fuerte’s harvest is over. But it’s not just an addition to the Fuerte…

ARPAIA: The other thing is is that the fruit hung on the tree better.

TWILLEY: Mary Lu is not yet done listing the Hass’s virtues.

ARPAIA: The fruit is very easy to handle. It hides a lot of blemishes when it’s ripe because it turns black.

TWILLEY: And, and, and. The Hass is also the only avocado that Mexico and Peru are allowed to ship to the U.S., which makes it a pretty popular choice there too.

ARPAIA: Because they have insect pests in their countries. And research that was done in Mexico indicated that the Hass actually is a very poor host to fruit flies.

GRABER: There are all sorts of varieties grown in Mexico, but the Hass is the only one they can export. So this explains why small, black nubby Hass avocados have come to dominate the supermarket shelves today. But why have avocados themselves become so super popular?

TWILLEY: Well, they weren’t, at least not during the great Hass-Fuerte battles of the 30s through the 70s. They weren’t big in the U.S. or much of the rest of the world. In Central America and the northern part of South America, though, the avocado has always been a hit.

LUIS MARIO TAPIO VARGAS: Here in Mexico in a commercial way avocado was grown in small orchards. Main type of avocado fruit was a small fruit and thin-skinned, with large seed and scarce pulp or meat. Low commercial value but good flavor.

GRABER: Luis Mario Tapio Vargas studies water and soil management at the National Research institute for Forests and Agriculture. He’s based in Michoacan.

TWILLEY: Even with the introduction of the Hass, which had more flesh than seed and a sturdier skin—even then, the rest of the world took some convincing. Part of the problem with the avocado was its name.

LARMER: In the early 20th century in the United States, it was marketed as the alligator pear. Which might explain why it never caught on because it’s not a great name.

GRABER: Not a great name at all. The California Avocado Growers’ Exchange complained in the 1920s that associating the delicious fruit with an alligator was, quote, ruining the avocado business!

TWILLEY: Eventually the growers got their way and we now call alligator pears by a bastardized version of the Spanish bastardized version of the Nahuatl word which means testicle fruit.

GRABER: Because testicle fruit also was clearly not going to be a winner.

TWILLEY: Testicles and alligators aside, the avocado had bigger problems that just its name. In the rest of the world, the places where the avocado wasn’t from—people had no idea how to eat it. It was a fruit, but it wasn’t sweet, it was sort of slippery, it didn’t really cook well.

LARMER: I think when people first encounter the avocado, they’re getting them kind of off the truck and they’re just not edible. They’re hard. They don’t really know what to do with them.

GRABER: So on top of all the avocado’s challenges, consumers are buying them unripe. It is not looking good for the avocado. So how did we get to today? Lauren Oyler wrote an article about the rise of avocado toast—yes, we’ll get to that—and she looked back at how a few bold eaters in the U.S. were at least trying avocados in the early 1900s.

TWILLEY: She found a New Yorker article from 1937, called Avocado, comma, or the future of eating, by one S.J. Perelman.

LAUREN OYLER: And he goes to a restaurant in Los Angeles and has an avocado sandwich on whole wheat and a lime rickey at a pharmacy called Best drugstores. And so at that point you can see at least that there’s the concept of avocado on bread is emerging in our culinary consciousness in America. And then I also founded a 1962 New York Times article that says you could put avocado in a toasted sandwich and that would be an unusual way to serve it.

GRABER: Lauren’s point is that most people were not eating avocados. There weren’t as many Mexicans in the U.S. back then, and most non-Mexican Americans at the time weren’t eating as many tacos or chips and guacamole as they are today.

TWILLEY: Most Americans at the time would not necessarily have known what guacamole was.

GRABER: Plus, avocados were seasonal and only grew in certain areas of California and Florida, and so they were expensive.

TWILLEY: In fact, at nearly 5 bucks an avocado, they were apparently often stolen from grocery stores. And they were marketed as fancy foods: if you really wanted to impress your guests, you could serve an avocado with lobster as a elegant appetizer. That’s actually how I first encountered the avocado—my mum would serve it at dinner parties with the hole where the pit used to be filled with prawn cocktail.

GRABER: Plus you know, the 60s and 70s, this is also the beginning of the whole crazy ‘fat is bad’ time in American history, and avocados are pretty fatty, and they would have been seen as unhealthy. So the California Avocado Commission responded with a marketing campaign.

TWILLEY: They poured hundreds of thousands of dollars in to this. The first step: convince folks that avocados are actually healthy.


TWILLEY: Yep, that sexy avocado fan is the actress Angie Dickinson, and she is lying alluringly on her side, dressed casually in gold high heels and a shiny white leotard, just, you know, scooping an avocado out of its skin with a teaspoon.

GRABER: As one does. In a white leotard.

TWILLEY: We’ve got the video on our website for all your avocado-eating wardrobe inspo needs.

GRABER: I can see how this commercial would send everyone running to the supermarket. But that wasn’t all the commission did. They funded studies showing that the fat in avocado helped increase nutrient absorption. They partnered with Harvard to promote the Mediterranean diet, full of so-called healthy fats. This was an all-out avocado blitz.

TWILLEY: But there was another problem. People were buying these fancy avocados while they were shiny and green and trying to eat them. Which was not nearly as fun and delicious as eating a ripe avocado.

GRABER: The commission even introduced a mascot called Mr. Ripe. As in, make sure your avocados are actually ripe! And to get some attention, they launched a contest looking for his perfect mate—Ms. Ripe, who would, quote, exemplify the California lifestyle of good health and healthy eating.

TWILLEY: But even with Mr. and Ms. Ripe AND Angie Dickinson encouraging folks to put their avocados in a paper bag or on the windowsill and let them ripen for a few days, the fact remained: it’s annoying to have to plan in advance to get a ripe avocado. Who shops four days ahead?

GRABER: And then, Brook Larmer told us that an avocado farmer named Gil Henry came up with a revolutionary idea.

LARMER: But the guy who I talked to in Southern California who helped come up with this this idea—he and his children went up to the local market in L.A. and watched people buy avocados and he realized that people would go up there and kind of feel around the avocado and if they didn’t find a ripe one or one that gave a little bit to the thumb push they would just walk away.

TWILLEY: In fact, the avocado commission installed a hidden camera in a California supermarket in the early 1980s, and the footage showed shopper after shopper squeezing the fruit and putting it back down. It was just lost sale after lost sale.

LARMER: And so he had this idea—we will do this.

GRABER: This was invent ripening rooms for avocados! Gil modeled his avocado ripening rooms after after banana ripening rooms. They’re basically refrigerated rooms where the avocados would hang out, and small amounts of ethylene would be pumped in. Ethylene is a plant hormone and it’s what causes the fruit to ripen.

ARPAIA: And so that’s very, very important commercially.

GRABER: This way, all the avocados ripen together, at more or less the same time, before they even land on the grocery store shelf.

LARMER: And so first in Ralph’s grocery stores in Los Angeles and then that expanded to Kroger which owned Ralph’s and that became something where that was also a factor in getting people to buy avocados.

TWILLEY: Today, all avocados go through this ripening room process. It’s revolutionized the avocado business—the chances that you can find a ripe ready to eat avocado at the store are approximately 100 percent better than they were in the early 1980s. And so shoppers now put those avocados in their basket after squeezing them.

GRABER: And a side effect of all of this is that it causes the Hass avocado to fully take over the market. Beforehand, when avocados were sold unripe, the green Fuerte ones looked nicer, they were shiny and green. But once they’re sold ripe, the Fuertes would show any bruises to the soft fruit, while the black Hass avocados hide any small blemishes.

TWILLEY: So, between this massive marketing effort, the invention of the ripening room, the name change, and the nutrition message, the avocado is poised to finally become a regular part of the American diet. But the thing that really pushed it over the edge? Much less glamorous than Ms. Ripe. It was a trade agreement.

GRABER: But before we get to how NAFTA led to the avocado’s world domination, we have some sponsors to tell you about.


GRABER: In 1994, the avocado finally hit the big time—because of the North American Free Trade Agreement. Yep, NAFTA.

LARMER: But something else had to happen first. There was a ban on Mexican avocados that was imposed way back in 1914, ostensibly over fears of boll weevils getting into the agricultural crops in California. And it protected the California farmers from infestation. But it also kind of protected them from cheap competition. So there was this great fear in the United States that opening the doors to Mexican avocados in this particular industry would would destroy the California industry.

TWILLEY: So when it came to the talks about the avocado during the NAFTA negotiations…

LARMER: Well, they were hardly talks, they were more arguments. The fights that went into trying to lift its ban were extremely heated. I talked to one U.S. distributor who said that he went into this meeting in southern California to talk about lifting the ban and he was a distributor so he favored bringing in Mexican imports. He said that he was spat at and shouted at and basically kicked out of the meeting.

GRABER: A few years after NAFTA was signed, the ban on Mexican avocados was finally lifted. At first it was just for 19 states in the northeast.

LARMER: Far away from California so that the New Englanders could consume avocados in the wintertime. That gradual incremental lifting of that restriction was full fully enacted by about a decade later. And that’s what really led to the explosion.

TWILLEY: And explosion is the right word.

LARMER: You know, back in 1997, Americans only consumed avocados in the summertime when the California avocados were harvested. None of those were imported. You know, today Americans can eat avocados year round almost anywhere—if they can afford it.

TWILLEY: Post-NAFTA, avocado demand has grown exponentially. Twenty-five years ago, Americans were eating barely one pound of avocado per person per year. Now it’s more than seven.

GRABER: The other thing that’s boomed is ways to eat all that avocado.

TWILLEY: To go back again to when I was a kid in the 80s, encountering avocados in England, we had them on the half shell. Like Angie Dickinson. Though not, I hasten to add, in a white leotard. You scooped out the flesh with a teaspoon. When the pit hole wasn’t being filled with something fancy like prawn cocktail, we used to put vinaigrette in there. But that was the only way I knew to eat an avocado.

GRABER: And I don’t remember even seeing anything like that, at least not in my house or my friends’ houses. I do think my family went out to kind of Tex-Mex restaurants on occasion. I remember one down the street from my house in the 80s.

LARMER: In the United States we have this Mexican-American community that is growing along with the explosion of Tex-Mex food.

GRABER: And so people like me and my family started to eat more guacamole in their everyday lives. It also became one of the foods popular to snack on during the Super Bowl, so the avocado commission decided to do a big PR push to get folks to eat even MORE guacamole during the Super Bowl.


GRABER: If it’s not obvious, they are trying to hypnotize us all into consuming even more guacamole. And it worked! Super Bowl weekend became one of the most important dates for avocado consumption in the U.S..

TWILLEY: According to the Mexican Avocado Association, a full twelve percent of America’s annual avocado consumption takes place during the Super Bowl!

LARMER: But 80 percent of those are imported and almost nine out of 10 of those imports are from Mexico—specifically from the state of Michoacan.

GRABER: So Americans are eating lots of avocados—that’s a win for the marketing campaign and, in theory, the growers. But these avocados are from Mexico! Sounds like exactly the nightmare that the California growers were worried about. So, did this mean that California avocado farmers were doomed? What happened to them?

LARMER: Well, remarkably this is a case of the rising tide lifting all boats. The year-round availability of avocados helped expand the visibility and attractiveness of avocados for everybody. So there was the growing market and the explosion among consumers only helped the Californians.

TWILLEY: Part of this is because Mexico’s production actually fills a gap around the California growers season. Under the NAFTA rules, California avocados get priority during their season, and Mexico, where avocados bloom four times a year, gets everything else.

GRABER: But even if California could extend its season dramatically, the state couldn’t possibly meet this new and still growing demand for avocados even if the farmers wanted to. There isn’t enough water and land.

LARMER: And so they really need this kind of extra input from Mexican avocados. And so the analysis is that there’s a real benefit to the United States economy—not just that California agricultural growers are spared but also it’s adding many, many jobs. I think there’s something like 19,000 jobs—new jobs for American workers. More than two billion dollars added to U.S. GDP simply by avocados.

TWILLEY: OK, so California farmers are happy, American avocado eaters are happy. But what about the place where all these avocados are coming from?

LARMER: In Mexico, most of the avocados are grown in a single state: the state of Michoacan, which is in south central Mexico, not far west of Mexico City, that goes down to the Pacific coast. And it’s not something that’s run by big agribusiness. It’s actually there are 20,000 individual orchards that are coordinated by a National Association.

GRABER: Michoacan is the only state that’s actually legally allowed to export avocados to the U.S. And the state has been completely transformed by avocados.

LARMER: It dominates the agriculture in that state.

TWILLEY: So what has the rise of the avocado meant for Michoacan?

LARMER: Well it’s interesting. Michoacan is a beautiful state. It has volcanoes and forests. I remember my first trip to Michoacan way back a few decades ago was to see the sanctuary where Monarch butterflies migrate in the winter from the United States. And you know, these are butterflies that have come three generations or four generations since the original migrants to the United States and they all come back to the same trees in a couple different preserves in Michoacan state and in the state of Mexico. That was my first trip and it’s just—it’s a gorgeous state.

GRABER: Those volcanoes and forests are part of why Michoacan is so great for avocados—it has really fertile soil and lots of rainfall.

LARMER: In California one of the real issues is water because avocado trees are extremely thirsty. Michoacan is blessed with, I think more than 70 percent of the orchards are naturally fed by springs, rivers, natural irrigation.

TWILLEY: So water usage is not a big issue, at least in Michoacan. The bigger environmental issue, at least for now, is what the avocado is doing to all those gorgeous forests.

LARMER: The Mexican environmental authorities estimate that about 50,000 acres a year are deforested in the state of Michoacan.

GRABER: It’s a big problem—and it’s not just because of avocado farms. But they are one of the causes. We asked Mario, the researcher who works on forest and water issues.

TAPIO VARGAS: The natural forests has been deforested for three main causes: illegal logging, forest fires, and avocado planting.

LARMER: And about 30 percent of that is due to avocado growing. The growers association will respond that well, most of these new orchards were previously used for other crops that have transferred their growing to avocados because they’re much more lucrative.

TWILLEY: So the avocado is not the only culprit here.

GRABER: And, in case you you were worried about the future of the Monarch butterflies, the forests that are being cut down for avocados aren’t the ones where the Monarchs go to spend the winter. Those are higher up in colder areas that aren’t as good for avocado farming.

TWILLEY: But still, as an avocado eater, I would love to enjoy my daily dose of creamy green goodness without contributing to deforestation. Mario told us that there had been some discussion about a law that would protect the forest and actually require avocado growers to return 10 percent of their cultivated land to wild forest.

TAPIO VARGAS: I am not optimistic of this situation.

GRABER: The growers fought back. And the government wasn’t interested in pushing this law, partly because it has bigger things to deal with, like drugs. And partly because, Mario thinks that corrupt government officials are making money from avocados.

TWILLEY: So what should a concerned avocado eater do? Mario says that in fact, we are the ones who can make a difference.

TAPIO VARGAS: The only way to protect is that, for example, that the United States said, I don’t buy you more avocados if you continue deforesting your lands.

GRABER: This strategy—that American demand can make a difference—it worked in the past. Mario said that avocado crops had been poorly handled, there were lots of pesticides left on and bacteria, but Americans wouldn’t put up with that. So Mexican farmers improved their farming methods to meet the demand. Mario thinks the same thing could happen with the forests—that if US consumers demand avocados that don’t contribute to deforestation, that could help save the forests.

LARMER: And but there’s also another problem in Michoacan, which is that this is the center of the Mexican drug war.

TWILLEY: Drug cartels in Mexico have made so much money from Americans looking to smoke pot and take meth that they have actually pretty much replaced the government in some places. They are super powerful along the west coast and in Michoacan too.

LARMER: So you can imagine when avocado profits in the last 20 years started to rise the cartels were quite interested. I mean in Michoacan avocados are known as oro verde, you know, green gold. And the cartels became kind of an insidious influence within the avocado industry. There were different groups, one called the Knights Templar who kind of had this medieval chivalric code and came in but extorted growers, kidnapped owners, usurped land. They created a kind of almost a war like situation for growers—it became very dangerous for the larger owners especially. Today those the Knights Templar have faded from the scene, La Familia Michoacana has faded from the scene, and now there’s a small splinter group called Los Viagras, which is apparently named for the leader who had heavily moussed hair that kind of stood on its end.

TWILLEY: On one level, if anyone is going to control the testicle fruit trade, it should be the Viagra gang. But seriously—cartel violence is a gigantic problem.

GRABER: You may even have noticed reports in the U.S. media in recent years about blood avocados. I mean, it’s not just that we don’t to eat something that’s contributing to deforestation—I definitely don’t want to eat something that’s supporting the cartels!

TWILLEY: But Brook tells us that in the past couple of years, things have looked up a little.

LARMER: In response to a lot of this cartel activity many of these smaller towns have have created self-defense militias, usually formed by the owners themselves. Many of the owners have teamed together to try to keep the peace and keep their avocados. There’s one place in particular called Tancitaro, which has become famous as the last place where it has this kind of self-defense militia. It’s like an 80-person force where they surround their town with checkpoints and the producers have to work with armed bodyguards. But they’ve now celebrated four years without a kidnapping which is considered a success. So the cartels are still an influence on it, although they haven’t really slowed down production, which is quite amazing.

TWILLEY: And again, like the deforestation issue, the cartel violence is not entirely the avocados’ fault.

LARMER: I mean, first of all, I think that the drug cartels were not created by avocados, they happened to attract the cartels because of their lucrative nature.

GRABER: And actually, Mario says that avocados have been really good for Michoacan in a lot of ways.

TAPIO VARGAS: The avocado in orchards have permitted that the people, the poor people of many communities that was in the poverty, now they are in economic best conditions.

TWILLEY: And those economic benefits means that more people can stay in their homes with their families.

LARMER: Michoacan is a huge sending community—or has been a sending area for migrants to United States. But avocados have kept more people closer to the land without necessarily needing to migrate.

GRABER: Great to know that we can enjoy Mexican avocados with very little guilt. Because frankly, what would happen to Instagram feeds of <illennials if you took away their avocado toast? Just kidding, don’t write us angry emails.

TWILLEY: And for even less guilt—if you want to get rid of that lingering worry that your avocados from Mexico are contributing to deforestation—right now the best you can do is look for an organic, Rainforest Alliance, or Equal Exchange label. Rainforest Alliance and Equal Exchange avocados are hard to find, and organic doesn’t specifically guarantee that the grower is not cutting down virgin forest, but it does mean that the cultivation is less intensive and doesn’t pollute the groundwater as much. Not a perfect solution, but one that means you can go ahead and have your avocado and eat it on toast … just don’t expect to be able buy a house as well.

GRABER: As some would have you think. We are coming right back to take our usual nuanced look at the strange phenomenon that is avocado toast.


OYLER: So I was actually talking to someone yesterday and I was like, oh I’m going to do an interview for a podcast about avocado toast and they were like yeah! what — it’s like — what is it exactly? I’m not really sure I understand? I’m like: it’s literally what it sounds like.

GRABER: It’s avocado. On toast.

TWILLEY: This is Lauren Oyler again, journalist and author of an in-depth look at the origins of avocado toast. And, in case you’ve been living in a cave for the past few years, avocado toast is having something of a moment right now.

OYLER: I feel like I came to avocado appreciation relatively late in life. I grew up in West Virginia and it’s not that we didn’t have avocados there but it’s not like one of the main food groups as it is in somewhere like New York or L.A. or even Berlin where I used to live.

GRABER: Lauren first noticed avocado being served on toast just a few years ago, when she moved to Berlin after college

OYLER: I don’t really remember eating it in college. And I graduated in 2012. And then when I lived in Berlin there are a lot of Australians living there and there are a lot of Australian cafes and I think that is probably the first time that I really noticed it on a menu.

TWILLEY: This is kind of late in avocado toast terms. Or at least in terms of the current wave of avocado toast. Because the question of avocado toast’s origins is a tricky one.

OYLER: Because you could certainly argue that avocado on a tortilla is the original avocado toast. right? But I think that’s a fundamentally different eating experience though it may be a predecessor to avocado toast—probably certainly is a predecessor to avocado toast.

GRABER: Which today is basically mashed avocado on toast, with maybe salt and pepper, and a few beautiful garnishes, like Nicky’s pickled pink radishes. That avocado toast is now found on the menu at restaurants and cafes basically everywhere. But Lauren wondered, where did it first come from, this current incarnation of avocado toast?

OYLER: There’s truth to the idea that Australia popularized avocado toast in the way that we know it today, which is sort of like a glamorous snack or meal that one can take a nice photo of for one’s Instagram account. Generally the first menu avocado toast is said to be at a cafe called Bill’s, I think, in 1993, in Sydney.

TWILLEY: Bill’s is a trendy all-day restaurant run by a well-known Australian chef called Bill Granger. He has confessed that he had no idea what he was starting when he first put avocado toast on his menu—he says he just thought avocado was a nice thing to have with a bit of tomato on toast.

OYLER: He published a recipe for avocado toast and he put in his cookbook and he was sort of like, I felt dumb putting a recipe for this in my cookbook because it’s so easy and obvious that you shouldn’t need a recipe. But I needed to fill a page.

GRABER: It wasn’t an overnight success. But then a little more than a decade later, an Australian chef named Chloe Osborne put avocado toast on the menu at Cafe Gitane in Manhattan.

TWILLEY: And then came Gwyneth. Paltrow, in case you’re not on first name terms. She put avocado toast in her 2013 cookbook, It’s All Good. And this, according to Lauren, is the moment when avocado toast went from being a thing you ate to a cultural phenomenon.

GRABER: So much so that Miley Cyrus has a tattoo of a half an avocado on her upper left arm. But when we say phenomenon—really, it’s kind of crazy how much the avocado and avocado toast, of course, have taken over.


OYLER: So that. But then I also talked to some people who grew up in California in the 70s, and they were like, yeah we ate avocado on toast too.

TWILLEY: Yeah, not everyone is on board with the Bill’s-Cafe Gitane-Gwyneth origin story for avocado toast. Turns out people have been mashing avocado onto grain-based products for a while.

OYLER: After I published that article someone messaged me saying that her sister or something had spent a lot of time in Tel Aviv and that they always ate avocado on toast too, so that she thought that that meant that they had invented it.

GRABER: This was my experience—I first fell in love with avocado in the 90s, when I was living in Israel, and everyone just sliced avocado and put it on bread and sprinkled some salt on it. And I was like, this is delicious. Not revolutionary, just delicious.

OYLER: But I think trying to pinpoint the origin of it is a fool’s errand.

TWILLEY: No shit. But the real question is why? Why has avocado toast transcended its status as snack to become a symbol of everything?

GRABER: Part of it is that it’s become something that somehow seems pure and fresh and healthy and the good fatty, and somehow just perfect.

OYLER: I think as a status symbol. Avocado toast does does sort of advertise a certain lifestyle, which is like a wellness, a healthy lifestyle, which now is a kind of status symbol. And along with, like, doing yoga or going to Soul Cycle or going on a vacation to, like, Joshua Tree or something, avocado toast can, like, signify a certain kind of person and a certain kind of aspirational lifestyle.

TWILLEY: And it turns out that avocado toast is the perfect visual aid to advertise that lifestyle. It is the Instagram food par excellence. Last July, British Vogue reported that 3 million new pictures of avocado toast are uploaded to Instagram every day! Which truly says something about our times.

GRABER: I can’t even wrap my head around that figure. So why in the world has avocado toast taken over Instagram? What makes it such a perfect model? Once again, Lauren has the analysis.

OYLER: I think the color green of an avocado is bright and alluring but it’s not so bright that you can’t pair it with other colors. So you often see like a radish on avocado toast or like shaved—maybe like shaved beets or some kind of beet-like thing and so with the contrasting with the pink or the purple, it looks really, really nice.

TWILLEY: It’s beautiful and healthy and… it’s expensive.

OYLER: So there was a controversy semi recently in which I think an Australian investor or a millionaire or some sort of rich Australian non-Millennial was deriding the Millennial generation and saying that the reason we couldn’t afford to buy houses was because we’re spending so much money on avocado toast and coffees that cost four dollars.

TWILLEY: A tsunami of people helpfully told this dude he had his head up his ass and the real reason Millennials can’t buy homes is not actually because they’re spending all their money on avocado toast.

OYLER: But because of the raging income inequality and the subprime mortgage crisis and all the sort of economic stuff that has been pushed onto us from the older generations. And while I agree with the structural critique of his statement, I also do feel like avocado toast is quite expensive. And also it’s something that you can make at home for very cheap. And so I don’t want to say I see where he’s coming from because it was a stupid comment. But avocado toast is quite expensive. I mean, like, you can get it for like 13 dollars in some places in New York. Which is more than I’m going to spend on a piece of toast, shall we say.

GRABER: Look, I get it, sometimes you’re out at a cafe and they have awesome bread, and they put fun garnishes on it, and you want a piece of avocado toast. For Lauren, though, it’s come to mean something more.

OYLER: When I encounter avocado toast on a menu today, I always have this sort of like pain—this feeling of yearning because I at least still cannot justify ordering it in a restaurant though I see people doing it all the time. And I’m always like if only I were— like I feel like there’s—at some income level I will be frivolous enough to order an avocado toast in a restaurant. But still there’s like a barrier to me. It just seems so, like, luxurious.

TWILLEY: When you hear about Miley Cyrus having an avocado tattoo or avocado toast breaking Instagram and denying a whole generation home ownership, you think: we must be at peak avocado. But no.

GRABER: Because the future of avocados? It’s probably not in the US at all.

LARMER: In the year 2010, there were fewer than two tonnes of avocados imported into China. A small sedan could carry that many avocados. But since then it has become much more widespread mostly among young Millennials and the upper middle class but as a healthy fruit. And it’s known in China as the butter fruit, which seems to me like a perfect name for the avocado because that’s exactly what it feels like when you eat it—so buttery.

TWILLEY: So OK, in 2010, there was a car-load of butter fruit sold in the whole of China. That was the situation seven years ago.

LARMER: Last year, 32,000 tonnes were imported into China. And this is partly a marketing campaign and also partly kind of a young urban middle class kind of reaching for a global craze.

GRABER: Brook says Chinese entrepreneurs are building ripening rooms for avocados. They’re starting to talk about growing avocados in China. We’ve had our boom here in the U.S., and now that boom is moving on to other shores.

LARMER: Chinese have an unbelievable ability to adapt and incorporate new things into their cuisine. They are omnivores of the first order and also have a very, very widely diverse palate. And the avocado is a flavor carrier. In China, as in Southeast Asia, they’re also able to see it as a fruit. They don’t mind a fruit that looks like a vegetable or using it both for sweet and savory outcomes.

TWILLEY: In fact, Brook says that in the southernmost part of China, near the border of Myanmar, avocado is already popular. It’s used in salads with tomato and onion, like a kind of proto-guacamole. And it also goes into shakes, where it gets blended up with condensed milk, sometimes with powdered chocolate added for good measure.

GRABER: This is pretty common around the world—you find avocado ice cream and avocado shakes. It’s only starting to catch on here—we still seem to think of avocados mostly in savory dishes. But Brook says we can’t even imagine how big avocados are going to get in China. The avocado’s journey from Mesoamerican backyards to world domination still has a way to go.

LARMER: One of the guys that I quoted in the piece, this guy Steve Barnett who’s one of the biggest distributors in the world, dreams like every entrepreneur of introducing four chunks of avocado in every bowl of noodle soup in China.


TWILLEY: But wait, there’s more—what about the new pitless avocados? And avocado hand? And the trendy new variety that is supposed to be better than the Hass, and I want to plant in my back gardenz, but is impossible to get hold of, it’s so hot?

GRABER: Well, you can find out about all of that if you are one of Gastropod’s special supporters and get our special supporter newsletter! Every episode, it’s full of fun stuff we just couldn’t fit in. It’s $5 bucks per episode donation on Patreon, or $9 bucks a month support on our own website, gastropod.com/support.

TWILLEY: Thanks this episode to Brook Larmer, freelance journalist, avocado fancier, and New York Times Magazine “On Money” columnist, and also to Lauren Oyler, freelance journalist and avocado toast aspirer.

GRABER: As well as to Mary Lu Arpaia and Eric Focht of UC Riverside and Luis Mario Tapio Vargas at the Mexican National Research institute for Forests and Agriculture. We have links to their articles and publications and websites on our website, gastropod.com


Cutting the Mustard TRANSCRIPT

This is a transcript of the Gastropod episode Cutting the Mustard, first released on February 27, 2018. It is provided as a courtesy and may contain errors.

ROSE EVELETH: So I’m Rose Eveleth. I’m the host of Flash Forward, which is a podcast about the future. But more importantly I am a very huge fan of mustard.

CYNTHIA GRABER: And you and I were actually talking about this, I don’t know, a year or two ago, and you were, like, you have to do an episode on mustard! So why are you obsessed with mustard?

EVELETH: So it’s funny—in thinking about this call we were going to have, I figured you would ask me that question and I realized that I don’t have a great answer. I mean it is objectively the best condiment. But that’s not the best answer. I mean it’s just really delicious, it goes on everything. But I wanted you all to do an episode on it because I am a fan of mustard and I consume a very large quantity of mustard, probably an embarrassing amount of mustard, but I don’t actually know that much about how mustard is made. Like, I’m familiar that there is a mustard plant and a mustard seed. But what actually makes different mustards different is actually sort of a mystery to me. I just eat them. I don’t know that much about them.

NICOLA TWILLEY: That’s what we’re here for, is to do the Googling that you can’t be bothered to do.

EVELETH: Exactly. I’m too lazy, I need an episode of Gastropod.

TWILLEY: Fortunately, Cynthia and I are not lazy at all ever in any way.

GRABER: I hope everyone believes you.

TWILLEY: And so Rose’s wish was our command. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber, and, as Rose pointed out, this is indeed an episode of Gastropod, the podcast that looks at food through the lens of science and history. We are happy to look into mustard, but Rose, in return you have to answer all my questions about what life might be like in the future. But first, mustard, what do you want to know?

EVELETH: I guess, you know, I eat a lot of mustard and I know a lot about the different kinds of mustard that I could purchase on the market, right? I know the, you know, various varieties of consumer goods related to mustard. I know a lot about how mustard tastes. I know nothing about the pre-going into my mouth parts of mustard. I mean I get the basics—there is a seed. You know, it’s like it’s in many ways like a lot of other things that are made from seeds. The powder seems obvious to me, right? It’s like ground-up seeds. Maybe I’m wrong about that. Who knows? You know, actually.

TWILLEY: Side note, which we didn’t say because we didn’t want to puncture Rose’s belief in all things Gastropod, but we didn’t actually know. Then. Now we do!



GRABER: Rose has been a mustard fan for a long time.

EVELETH: I used to be an athlete in, like, high school. And so I was constantly at various athletic events and they often would sell pretzels and hot dogs and stuff like that. And I think that was when I realized that mustard is far superior to ketchup. And so I was always really into mustard. But I don’t actually know that much about, like, what the process is to take a mustard plant, and if there are, like, multiple different kinds of mustard plants, and that’s how we get these various different kinds of mustard. Like what makes Dijon, Dijon? Is it the plant, is it the seed, is it the processing? Is it some combination of all of those things? And so I was just curious about what where mustard comes from and sort of how all of these different types of mustard are made.

TWILLEY: So many questions! So many answers! But let’s start by getting our basics down: what exactly is this mustard plant of which Rose speaks?

PATRICK EDGER: So the mustard family actually consists of about 3,600 different species and so there’s quite a bit of diversity. Most of the species are the types that you would see growing in the cracks of sidewalks.

GRABER: Patrick Edger is assistant professor of horticulture at Michigan State University.

EDGER: The mustard family really consists of, you know, lots of wild species, but most notably the majority of the vegetable crops that you probably eat and consume every day. You know: broccoli, cauliflower, Brussels sprouts, kale, radishes, as well as like wasabi as a condiment or mustard as a condiment. But in addition there’s a lot of oil-seed types. So we would have things such as, like, rapeseed or canola oil that we would cook with. Those are all from the very same family.

TWILLEY: Fortunately, for the sake of my sanity, the kind of mustard that we can buy in the store labeled as mustard only comes from three plants within this enormous family: black mustard, brown mustard, and white mustard. Confusingly, the white seeds make yellow mustard, and the brown seeds are a kind of beigey-yellow inside, so the whole color terminology is not particularly helpful. But all three kinds of mustard seed have one thing in common: they’re tiny.

GRABER: And this is just the point of another mustard story Rose told us.

EVELETH: Yeah, so my grandparents on my mom’s side are Catholic and when I was a kid my grandma gave me this charm bracelet. And it had all sorts of various Catholic charms on it, it had obviously a little cross but it also had a bunch of other little charms that were relevant to various parts of the Bible or stories or whatever it was. And I was a very, like, tomboy kind of kid so I was, like, I’m not going to wear jewelry, this is stupid. But there was one charm on the bracelet that I was really into because it was this tiny little magnifying glass that you could flip open and you could look into it. And it just magnified one mustard seed. And I guess this comes from a parable of the mustard seed in the Bible.

GRABER: I had never heard of this parable of the mustard seed before—probably because I’m not too familiar with the New Testament.

TWILLEY: Whereas I had, despite never consciously listening in church at school.


EVELETH: Yeah, so I should say that I’m not a scholar of the Bible and nor am I a believer. So, like, I’m not an expert here. But it’s basically about how the mustard plant is really large—they can get to be nine feet tall. And for a plant that big they have small seeds. And so the story, the parable in the Bible, is kind of about that size difference—that when that tiny, tiny seed is planted in the earth it makes a giant plant. It’s kind of one of those “don’t judge a book by its cover,” I think, ideas—that even though the seed is so small it can become this great huge beautiful thing with birds and, you know, branches and all this stuff. So that’s kind of, I think, what the parable is about—if I’m interpreting it correctly, which I could be not doing.

TWILLEY: I am not a believer or a Biblical scholar either, but, from the best I can tell, this mustard seed story is actually more about how the kingdom of God will grow from its tiny beginnings.

GRABER: Which I still don’t really get, but that’s fine. It’s not meant for me.

TWILLEY: But this Jesus connection has an interesting side note attached to it. Supposedly because Christians were so attached to their mustard seeds, they carried them with them and scattered them as they walked, and so mustard plants grew along their trails. One of the places you hear about this happening is in California. People say that one of the early missionaries, Junipero Serra, walked north from the San Diego mission in the 1700s, scattering mustard seeds as he went. And the resulting quote “Bible trail” is apparently still marked by mustard plants today.  People say the same thing about pilgrim routes on the east coast of the U.S. too. You’re supposed to be able to see them clearly from above, thanks to their bright yellow flowers.

GRABER: There’s a Gastropod fan and supporter who happens to—okay—be a friend of yours Nicky, AND he also happens to work for a company that specializes in satellite mapping. So we figured, maybe he’d know if this supposed mustard trail is indeed visible from space. Do the satellite images show the particular visible signature of mustard?

TWILLEY: So my friend Wayne does actually have a real job, so he could not devote too much time to the search, but he told us that unfortunately, most purchasers of satellite imagery actually want something called “leaf-off images”—these are images captured in the winter where there isn’t a ton of foliage covering up all the other features they’re interested in. So, long story short, no luck.

GRABER: If anyone knows whether this California mustard trail tale has been proven true or false, please get in touch!

TWILLEY: But Rose doesn’t love mustard for its religious connections. She loves it because of its heat—its pungency and flavor.

EDGER: That sharp, pungent, bitter flavor that we sense are from compounds called glucosinolates. There are roughly a hundred and twenty-some different compounds and depending on the abundance and the profile of, like, the composition of these various compounds, that’s what gives cruciferous vegetables that sort of flavor.

GRABER: Now remember, these cruciferous vegetables—there are a lot of them: kale and Brussels sprouts and broccoli, just to name a few of my favorites. They have some of these glucosinolates—maybe slightly different ones with slightly different flavors. But things like kale and cabbage don’t have nearly as much pungency as mustard does.

TWILLEY: In other words, there’s a whole spectrum of spiciness between species, depending on which and how much of those 120 different glucosinolates they have.

GRABER: But here’s a question: What purpose does this pungency have for the plant?

EDGER: Yeah, so like most organisms plants do not want to be predated on. They don’t want to be consumed. And being a plant when you’re fixed in a location and you’re constantly combating insects and fungal pathogens and bacteria and viruses, you have to have some way to defend yourself. And so most of the flavors or things that we describe as flavors are actually chemical compounds that plants used to ward off being predated upon. And glucosinolates are one of those examples.

TWILLEY: Unsurprisingly, there’s an evolutionary reason for why the seeds of a mustard plant—the part we use for making the condiment—are much spicier than its leaves, which we use in a salad.

EDGER: If the purpose of a plant is to pass on their genetic material, they will invest quite a bit of that into their seeds to protect actually that next generation. So in mustard seeds, there’s lots of glucosinolates.

GRABER: These glucosinolates are really poisonous to some species—they kill insects.

EDGER: Glucosinolates are actually incredibly toxic even to the plant. The plants will actually sequester a lot of the precursor molecules in vacuoles that safeguard it even from the cell. So that’s how toxic they are.

GRABER: Those special containers get broken open when an insect starts chomping.

TWILLEY: But here’s where these mustard toxins gets even more interesting. A couple of years ago, Patrick published a paper tracing what he calls the great butterfly-mustard arms race. The story starts 90 million years ago, when the first mustard plant ancestors figured out how to stop caterpillars from eating them—by producing some glucosinolates.

EDGER: When the compounds first evolved, it would have been an instant barrier for predation, right? And so that actually would have permitted that ancestral plant that just evolved this novel trait to diversify very rapidly across the landscape. Because now it basically has a wonderful sort of set of armor for any predation to occur.

GRABER: So now the mustard great-great-great-etc. grandparent is super chill. The caterpillar can’t eat it, it’s free to grow and spread across the landscape. For at least a few million years.

TWILLEY: But the caterpillars aren’t done. They are hungry, hungry caterpillars.

EDGER: So the insects evolved a enzyme, a novel enzyme, a brand new gene, that actually, as the insect is consuming these glucosinolates, actually cleaves the compounds—this chemical compound—to make it an inert structure.

GRABER: So now these glucosinolates are no longer toxic to the caterpillars, and now the caterpillars are the happy ones.

EDGER: We then see, as one would predict, it now has a buffet.

GRABER: They can eat as much as they want of this spicy plant that no other insect can snack on.

TWILLEY: And now it’s the caterpillar’s turn to spread and diversify and generally be boss. But, as you would expect, the mustard plant ancestor does not take this lying down. Like Patrick said, it’s an arms race.

EDGER: We actually see repeated cycles of this—minimally, three of them that have occurred over the last 90 million years.

GRABER: This is plant-animal warfare, people. For his experiment, Patrick and his colleagues studied hundreds of species of related plants—plants that trace their ancestry back to those original, millions-of-years-ago genetic splits. This way they could figure out the timeline of when each side temporarily was victorious.

TWILLEY: They could see these big leaps forward in mustard defenses written in the plants’ DNA. One thing to know: lots of plants pass multiple copies of their genomes down to their offspring, instead of the single copies that we humans pass on to our kids. And this extra genetic material gives the mustard plants so many options to play with—so many different pathways to make new, improved glucosinolates.

EDGER: After every set of duplications, you basically would have a new and fancier set of defenses. And this escalated over time until the present day where many of the mustard plants have, you know, over 100 compounds in them.

GRABER: Here’s one of my favorite points in this whole research: this arms race led to amazing success for both insects and plants. As the war went on, it actually created many, many new species of both brassica and butterflies. Both dramatically increased in biodiversity and habitat. It is at least partly due to this arms race that we have kale and collards and cauliflower and Brussels sprouts and horseradish and radishes and mustard and everything.

EDGER: As the brassicaceae were more successful, that actually permitted subsequently the butterflies to be more successful. But then they also each of them have shaped the underlying genomes or even the phenotypes of one another. Ultimately, we really have the butterflies to thank for mustards, right? Mustard compounds. None of this would have existed if it wasn’t for this arms race.

TWILLEY: Next time you squirt mustard on a hot dog, remember to thank a caterpillar. So that’s cool, but my favorite part of Patrick’s experiment is that as part of his whole process, he found plants that are living today that have the level of glucosinolates that mustard used to have in the past.

EDGER: There are actually relatives from those ancestral intermediates that you can go out and you could potentially sample. And that was part of the study. We found all these sort of intermediate lineages—remnants. And from that, we can actually make estimates of what those profiles probably were like. We can’t be very definitive about it but we can make really pretty solid estimates of what those ancestral states would have been like, going back to at least 90 million years.

TWILLEY: I temporarily lost my mind for a minute when I heard this and decided that what Cynthia and I needed to do was track down all these milder-tasting relatives and do a mustard tasting through evolution, from bland to fiery.

GRABER: That sounds awesome, of course, but then you realized that it’s just the two of us and we have to put out shows and that would take months of plant collection and seed crushing.

TWILLEY: But if some millionaire mustard-ophile out there would like to fund this quest, I am available to talk offline. The 90-million year mustard tasting awaits!

GRABER: And I will happily join in. So Patrick and his colleagues wrote about this butterfly-mustard arms race. But here’s something that might scare you: the battle is not yet over!

EDGER: We see this constantly happening. So a lot of cabbage butterflies, if you grow any cruciferous vegetables in your backyard—broccoli or cabbages or cauliflower or what have it—you’ll see lots of cabbage butterflies always trying to predate on it.

TWILLEY: And that means that the plants need to be upping their game. And they will.

EDGER: I could imagine a mustard being spicier.

TWILLEY: Not just spicier, but even with a slightly different flavor profile, from new variations and combinations of these glucosinolates. Basically, we can’t even imagine the mustards of the future!

GRABER: Rose, this is the episode you get to make!

TWILLEY: Right, you do mustards of the future, we do the mustard science, and, next, mustard history.


HAYLEY SAUL: At this stage, I would say that these findings are the earliest conclusive use of spice for a culinary purpose.

GRABER: Hayley Saul is an archaeologist at Western Sydney University. And, a few years ago, she and her colleagues discovered the earliest known example of spiced food in human history—dishes perked up with, yes, mustard.

TWILLEY: OK, picture the scene. It’s more than 6,000 years ago, and you are in northern Europe, eating a plant called garlic mustard.

SAUL: So there were three main sites where we found the evidence of garlic mustard. One of them in Germany, which is a site called Neustadt, which is actually now underwater. It’s been excavated underwater. That inundation is actually one of the reasons why the pottery and the pottery residues are very well preserved because the waterlogging is great for preservation. And the sites in Denmark—so the sites are called Åkonge and Stenø,and they’re located on the edge of a bog.

GRABER: There are a lot of sites like these found near water, because water is a great source of food. But the people who were living at these sites, were they just hunting and gathering all the wild plants and animals that lived in and near the water? Who were these people?

SAUL: So, you know, all of the sites actually span the sort of Mesolithic/Neolithic transition, which is the time at which people were starting to just domesticate and experiment with domesticated plants and animals. So the people that lived kind of in the Mesolithic tend to be associated with hunting and gathering. But it’s actually much more complicated than that, really. It wasn’t the case that people just gave up on hunted and gathered foods and then adopted these new, more superior types of domesticated foods. They were actually combining things and it was just a period—I like to think of it as a period that was very creative. And there were new types of food coming in but people were starting to sort of explore how they can combine it with food that they’d used for years.

TWILLEY: What Hayley’s saying is surprising to me. I don’t tend to think of Mesolithic or Neolithic people as being culinary wizards or experimenting with their food to create new textures and flavors.

SAUL: I think there’s been a kind of an assumption in general that in prehistory, people were driven by just the need to get a certain amount of energy and that there was nothing particularly artistic about food practices in prehistory. And in part that’s brought about just because of the techniques that we have and the difficulty of finding certain evidence. So it’s quite easy to document animal bones on a site and slightly more difficult to document plants because they don’t preserve very well.

GRABER: In the past, scientists have been able to figure out what people were eating on a kind of more general scale—did they get more of their calories from protein or from fat, did they go fishing, or were they butchering domesticated cattle? But, until recently, it’s been much more difficult to get a fine-grained look at the flavors of the foods prehistoric peoples were cooking. But now, there are new techniques that Haley says can give a higher resolution look at ancient diets.

TWILLEY: These higher resolution techniques include starch analysis, as well as drilling into food residue to analyze the fats. There’s also a kind of microscopic analysis to match the tiny fossil remnants of plant cells, which are called phytoliths, to a catalog of different plant species collected from the area. The combination of all these techniques, plus how well preserved the food residues were at these sites, meant that Hayley and her colleagues were able to get that more nuanced and detailed picture of what these early northern Europeans were eating.

GRABER: And there was a lot of food residue for Hayley and her colleagues to analyze.

SAUL: In some cases it was up to a centimeter thick, because the pottery wasn’t necessarily cleaned. So it was just becoming more and more carbonized, and thicker and thicker residues. A bit like you would use a skillet, the flavor is partly brought to the food because the skillet is sort of reused again and again and again. And it’s only when the carbonization of that residue becomes so distasteful that the pottery is actually thrown away into the lake or into the sea. And at that point, it’s just like a record of reuse and a kind of build-up of all of these different meals that the pots been used for.

GRABER: And Haley’s big find from this food residue? These Mesolithic people were revving up their stews with a plant called garlic mustard. I know I said this already, but—drumroll!—this is the earliest known culinary use of a spice in the world.

SAUL: It’s from the seed husk, the actual sort of hardened shell of the seed, which has a flavor, if you grind it up, much like mustard.

TWILLEY: Hayley was able to figure this out by comparing the phytoliths—these plant micro-fossils—to the microscopic structures you find in garlic mustard today.

SAUL: I had to do a lot of just going out into the countryside and foraging for plants that were edible and, you know, making up the reference collections and things. And it’s one of those plants that you could so easily overlook. It’s just everywhere. And once you get your eye in you can see that it’s everywhere. It’s a plant that’s available across the whole of Europe, right into India and parts of Asia as well. But it’s not just usable for the seeds. The leaves of the plants are edible as well. The reason it’s called garlic mustard is because the leaves have a very garlicky aroma but the seeds have a very mustardy flavour. So you can sort of combine two different flavors in one plant really.

GRABER: That sounds delicious. But we were wondering—maybe garlic mustard was a major source of calories for the folks in these settlements. How can we know it was being used intentionally to flavor their food?

SAUL: The seed itself of Alliaria petiolata is very small and it’s woody. Some people have suggested that it has properties for preservation. It may have medicinal properties. But, because it’s so woody, in terms of delivering anything like energy or a great deal of vitamin nutritional value, it doesn’t really do that. So it seems to be much more that it’s being used at least in part because of its aromatic properties. So it is imparting flavors into the food.

TWILLEY: Basically, it turns out that Hayley is pretty confident that Mesolithic people had Rose Eveleth-style levels of enthusiasm for mustard. They too thought that there was nothing that didn’t taste better with some mustard!

SAUL: So we were finding from the lipid residue analysis that they were combining garlic mustard with marine fish.

GRABER: They also made stews of garlic mustard and meat from animals they either hunted or raised, like cattle or deer.

SAUL: It’s such a common spice it’s almost like they’re using it as we would use salt and pepper. And that suggests to me that it could have an even longer history. But we just don’t know at this stage.

GRABER: And actually, there are even older sites around the Mediterranean that have plant remains from other spices and herbs—poppy, cumin, and coriander—but the plant bits are not embedded in cookware. So we can’t be positive that people were actually eating these spices. But maybe they were.

TWILLEY: Really, though, the important question here is, what did these mustard-spiced dishes taste like? Fortunately, Hayley can answer that one too.

SAUL: Because my research involves me sort of going out and foraging for plants for my reference collection, the temptation is always there to try out what the flavors of those different plants were, yeah, so I have made some unusual concoctions of my own. But if you can find some garlic mustard, just grinding it up in a pestle and mortar and you can smell the mustardy flavor as you’re grinding it as well. And it’s delicious in a nice stew.

TWILLEY: Yes, that’s right: Hayley made her own Mesolithic garlic mustard stew.

SAUL: I used it with some venison. My dad’s a butcher, so I managed to get a nice cut of venison.


SAUL: It did taste quite contemporary. It’s not such a strong flavor as the sort of mustard that you would get in a pot. But there is definitely a sort of flavor of mustard.

GRABER: I love the idea that the earliest known use of spice involves garlic mustard. Two delicious flavors in one plant. But, for Hayley, even more importantly, this finding helps us rewrite the stories we tell about the people who were alive back then.

SAUL: It’s easy to fall back on the idea that people were sort of caveman-like and, you know, they were just out to sort of eat as much and as often as they could because they never knew when their next meal was, and things. But actually I would say that they were extremely sophisticated, and they had such sophisticated skills at acquiring food that they could sort of be really creative about the ways that they were combining foods.

TWILLEY: This is another thing that Rose and our Mesolithic friends have in common: mad mustard-pairing skills.

EVELETH: I put it on everything. I mean, I’m a big carb person. So, like, any kind of bread product, it’s good on. Olive bread with mustard is extremely delicious. I mean, obviously there are pretzels, but you can also put mustard powder on things like popcorn. So, like, a little bit of soy sauce and mustard powder on popcorn is delicious.

GRABER: I’d love to try that popcorn. But so I was wondering, you know, can you walk us over to your fridge? Tell us about how many jars you have and could you list some of the ones that you see?

EVELETH: Yeah. All right, I will—I’ll take you over. Hopefully my dog doesn’t get too interested in what we’re about to do. Okay, I’m opening the fridge. Let’s see, where are we. So there’s this great mustard place called—I’m going to mispronounce it. Maille? Maille? M A I L L E. Okay, so we have a bunch of those. I have a walnut mustard from them. I have a Dijon blackcurrant liqueur mustard from them, which is really good. It’s like—it tastes like Thanksgiving. It’s amazing. Really good on French fries actually, because, like, they’re sort of a good vehicle for any kind of mustard but they taste like Thanksgiving French fries. I have a blue cheese mustard which is super strong. You kind of have to, like, be a little gentle with this one. We also have an amber ale honey mustard from this farm up in Vermont that is near a place where we go skiing every year. We, of course, have sort of the standard spicy brown for sort of hotdogs and all that stuff.

TWILLEY: There’s more—many more jars. The thing is, it’s not just Rose that’s crazy about mustard. Her partner Robert is too. It’s actually central to their whole relationship, at least in terms of condiments.

EVELETH: We have a running joke, because I subscribe to the Mustard Museum’s newsletter, and it’s sort of full of mustard information. And a couple of years ago, they sent one out and that was, like, you know, we do weddings. And I don’t know if they were serious or not but we have a running joke about getting married at the Mustard Museum.

GRABER: Nicky, you and I did not have wedding plans.

TWILLEY: Because we’re already work married.

GRABER: But we did actually visit the Mustard Museum. It’s just outside Madison, Wisconsin, and we happened to be in town to do a Gastropod live show. When in Madison, go see mustard, apparently.

BARRY LEVENSON: So anyway we’re going down into the museum: the world’s largest collection of mustard, mustard memorabilia, and fine mustard art.

TWILLEY: Barry Levenson is the founder and curator of the National Mustard Museum. He’s a lawyer with a serious mustard obsession.

LEVENSON: We’ve got nearly 6,000 different mustards here. So, in addition to American yellow mustard, classic French mustard, you have horseradish mustard, you have whole grain mustards. We have hot pepper mustards. We have herb mustards, we have fruit and vegetable mustards. We have garlic mustard. We also have spirit mustards, which would be mustards made with beer, with wine. We have exotic mustards. The exotic mustard category can be anything from curry mustards to truffle mustards to mustards with ginger. Right now, we’re standing in front of some of the French mustards.

TWILLEY: But before things get even more insane—although personally I think getting married at the mustard museum is already pretty insane, and having 6,000 jars of any condiment is definitely a warning sign—we need to back up. How did we get from garlic mustard seed stew to the condiment-filled jars we know and some of us love today?

GRABER: Before we clear your sinuses with some strong Dijon, we have a sponsor to tell you about.


GRABER: To get to France, first we have to go back to ancient Egypt.

LEVENSON: We also know that the ancient Egyptians would chew mustard seeds along with their meats and that would flavor it. But they would just take the seeds, because mustard seeds themselves are inert.

TWILLEY: There’s actually a chemical trick to mustard. So: the glucosinolates in mustard seeds—they’re slightly different compounds in black vs. yellow vs. brown mustard seeds but they work the same way. Which is that they they react with a particular plant enzyme in the presence of cold water to produce that fiery essential oil of mustard. This multi-step trigger process is another way that the plant holds fire until the caterpillar actually crunches into it and sets off that reaction.

LEVENSON: It’s only when combined with some liquid do they release their heat and their pungency. As a result, that’s what the Egyptians would do. They’d say, okay, have some meat and chew on some mustard seeds.

GRABER: Then the Romans decided to turn mustard into a sauce.

LEVENSON: We know that the Romans were using mustard seeds in some of their sauces and then that migrated into the Roman Empire, specifically into the area now known as Dijon, where the monks were making pretty much what we know as mustard today back in the 12th and 13th centuries.

TWILLEY: The first reference to mustard in the Dijon archives occurs in 1336—it’s a record of a whole cask of mustard being consumed at a banquet. So mustard was already a big deal. The first ordinance specifying how to make Dijon came at the end of that century. Basically, soak the seeds, crush the seeds, and then add vinegar to the paste. To go back to our chemistry for a minute, using an acidic liquid like vinegar puts a brake on the reaction, which gives the resulting mustard a long-lasting, slow burn—as opposed to the quick, pungent hit of mixing it with water.

GRABER: Dijon mustard got super popular in 1756. That’s when a major mustard maker in Dijon changed his recipe from vinegar to verjus—it’s a juice made from unripe grapes, and it’s not quite as acidic as vinegar. Today, if you buy Dijon mustard, it doesn’t usually have verjus, but the makers still try to make it taste like the recipe that made it famous. They’ll often use a combination of white wine and vinegar.

TWILLEY: Technically, Dijon is supposed to only be made with either black mustard or brown mustard seeds. But basically nobody uses black mustard commercially because the seed heads are so fragile that you have to harvest it by hand.

GRABER: Seventy to eighty percent of the mustard seed exported to make condiments comes from industrial fields in Canada, which happens to be the world’s mustard basket. And Barry says a lot of those mustard seeds go to France.

LEVENSON: France, of course, is known for mustard. The per capita consumption of mustard in France is greater than any other country.

TWILLEY: Since the 1800s, Dijon has been found at tables throughout France. In my home country, though, we developed a rival: Tewkesbury mustard, which is mustard mixed with its close cousin, horseradish, for a little extra something something. This mustard was sold and transported dry in balls, known as Tewkesbury fire balls. They were a staple in English kitchens in the 1600s.

LEVENSON: Shakespeare loved mustard and wrote about mustard in several of his plays.

GRABER: Shakespeare even used this famous Tewkesbury mustard in one his slightly less famous plays, King Henry IV Part 2. He wrote, “His wit’s as thick as Tewkesbury mustard.”

TWILLEY: This is not a compliment.

GRABER: Barry has his own favorite Shakespearean mustard quote.

Barry: “What say you to a piece of beef and mustard? Aye, a dish I do love to feed upon,” from Taming of the Shrew.

TWILLEY: Here’s the Shakespeare mustard reference I found surprising though: eye of newt, which is one of the things the witches stir into their cauldron in Macbeth—”eye of newt and and toe of frog, wool of bat and tongue of dog,” etcetera, etcetera. So eye of newt—I always thought that was the eye of a newt. But it isn’t! It’s an old name for a mustard seed.

GRABER: Rose, the rabbit holes you’ve sent us down! But Shakespeare’s Tewkesbury isn’t the most famous British mustard today.

LEVENSON: That would be Colman’s. The classic hot, just good, strong mustard that just kind of goes right up in the nose.

TWILLEY: Colman’s in the yellow tin—it’s *the* British mustard.

LEVENSON: Yeah, Colman’s dry is kind of the gold standard.

TWILLEY: The thing about Colman’s is, as Barry points out, it was originally a dry mustard—and you can still buy it that way today. I have two tins of Colman’s mustard powder in my kitchen as we speak. But grinding and selling dry mustard as a powder—that actually wasn’t Jeremiah Colman’s idea.

GRABER: The inventor of powdered, dry mustard is lost to history. The only record comes from an article published in 1807, in the Gentleman’s Magazine. And the author wrote that, in 1720, quote, “it occurred to an old woman of the name of Clements, resident at Durham, to grind the seed in a mill and to pass the meal through the various processes which are resorted to to make flour from wheat.”

TWILLEY: Ms. Clements’ mustard flour was a huge hit. Even George the First gave it the thumbs up. But she kept the secret to herself for many years. Jeremiah Colman was originally a flour miller, with a mill of his own. He didn’t turn to mustard until nearly 100 years after Ms Clements’ big breakthrough. But then he conquered the British mustard market, with a special blend of locally grown white and brown mustard seeds ground to a fine powder.

LEVENSON: Colman’s mustard was just dry mustard for the first 60 or 70 years before someone decided at Colman’s, well, why don’t we actually make the mustard condiment?

GRABER: So while Dijon is made from brown mustard seed, Colman’s is a blend of white mustard and brown mustard seeds. Brown seeds, like the ones used in Dijon mustard, they give you more of a horseradish-y, sinus hit.

LEVENSON: It gives you more of that nose hit as opposed to the yellow seed, which is more pungent just on the tongue.

TWILLEY: So France has its favorite mustard, Dijon, England has Colman’s, but in America, it’s all about French’s. So what’s that?

LEVENSON: That came about a little over 100 years ago, when Mr. French decided that even though there were European mustards, they weren’t all that popular. What this country needed was a brightly colored, happy mustard and that’s what French’s mustard has been.

GRABER:  Actually French’s mustard—it first came out at the turn of the last century—it was originally called “French’s Cream Salad Brand.” Not only was it bright yellow because Mr. R. T. French added turmeric to the recipe, but it was also creamier and sweeter. And it was a huge, huge hit almost instantly in America.

LEVENSON: It is generally made with the yellow seed, so it is going to have a very different kind of flavor profile. And that’s the kind of thing that when you go to the ballpark, I think you’ve got to have yellow mustard at least on that first dog. Because you hold up the hotdog, you know, and you see the blue sky, the green grass, the brown base paths and there’s just something about that yellow squiggle of mustard that makes life so worth living that day.

GRABER: Oh Barry.

TWILLEY: People have strong feelings about mustard.

MADHUR JAFFREY: It’s very important and it’s an ancient seed that we’ve had forever.

GRABER: Madhur Jaffrey is an actress and food writer. She’s probably the most famous writer of Indian cookbooks—she’s the person whose cookbooks helped popularize Indian cooking at home in the West.

TWILLEY: We’ve been stuck in Europe and America so far this episode, but mustard is global. And India has its own serious, long-term mustard thing going on. It’s not a condiment-based relationship, but it’s central to Indian cuisine

JAFFREY: It’s been amongst our two hot spices that originated in India. We started out thousands of years ago with mustard seed and black pepper. Those are native to the region and those were the only spices we had that were hot, and chiles of course came much later. So for many centuries, they were even more important than they are today, but they’re still very important today, because one of the oils that we cook with, which is very important, is mustard oil.

GRABER: Mustard seed and, even more importantly, mustard oil is found in kitchens throughout the Indian subcontinent.

JAFFREY: It’s used for cooking a lot of food in several states. Bengal cooks a lot with mustard oil. Kashmir cooks a lot with mustard oil. So these are two states where it’s almost the state oil. And there are certain dishes that would be cooked always with mustard oil. If you’re steaming a fish, you will definitely use some mustard oil. In Bengal, if you are making this muri, which is puffed rice, you’ve puffed it and then you want to dress it quickly with different things, you’ll put, among other things, mustard oil on it and have it for breakfast.

TWILLEY: So but here’s what’s weird. Mustard oil is banned in the U.S. as a food. It has been since the 1990s.

JAFFREY: When I buy mustard seed oil, it says on top: “Use for external purposes only.” People in India eat it and survive and nothing happens to them and they live long lives. We put it on babies, we—you know — but externally we put it on babies. But I keep reading it and ignoring it. It’s just like what they used to say with coconut oil. “Don’t cook with coconut oil.” And people go through fashions and suddenly now everybody is cooking with coconut oil as if it’s the best thing in the world.

GRABER: You might think that maybe the U.S. government was afraid of those pungent, insect-fighting glucosinolates. But no. The FDA thinks the problem comes from a fatty acid that’s found in the seed. Apparently tests on rats show that in high doses this particular fatty acid can cause heart lesions. But frankly, as Madhur says, literally billions of people have been cooking with mustard seed oil for thousands of years.

JAFFREY: I wouldn’t give it up. No. It is in a lot of things that I cook. I cook everything from all over India and I use it all the time.

TWILLEY: For Madhur, the magic of mustard is in the way you can manipulate its heat.

JAFFREY: It’s like a Jekyll and Hyde of both spices and oils. If you use it plain, it’s quite pungent. So when we want that pungent flavor, we use it plain. But if you heat the oil or if you pop the mustard seeds, they turn sweet and nutty. So it depends on what we want. It can change its shape, as it were.

GRABER: So in India, cooks know that cooking heat tames the fieriness of mustard seeds and oil. But Barry says condiment markers can use other tools to manipulate that heat, too.

LEVENSON: Which seed you use, how much water, how much vinegar is going to be used. There are all kinds of ways that mustard makers are able to change the heat of the final product.

TWILLEY: In fact, mustard is surprisingly nuanced. You think of it as this blast of heat on a sandwich, but, depending on how you make it or how you pair it with food, mustard doesn’t have to steal the show—it can fade into the background and just make everything else taste better.

GRABER: I never really had strong feelings about mustard one way or the other, unlike all of our guests this episode, but the bagel shop near me uses mustard butter on their bagel-egg sandwich and it’s mind-blowing. So I also started using a layer of mustard in my savory galettes—these are free-form pies—and it totally ups the game.

TWILLEY: Whole-grain mustard smeared inside the pastry shell of a quiche, before you add the filling: unreal. And mustard powder is my secret ingredient in cheese straws. But Barry and Rose have taken this pairing game a little further.

LEVENSON: It’s something that you can also use in brownies because it accentuates the flavor of chocolate.

EVELETH: This is going to sound disgusting to a lot of people but I think it’s delicious: a little bit of mustard on Oreos is extremely good.

GRABER: Wow, that is an unusual one.

TWILLEY: Wait, wait, wait so are we talking like French’s here or what are you doing? Like, how is that?

EVELETH: Like you sort of dip a double-stuffed Oreo into like, a little bit of mustard, in Dijon mustard.

GRABER: And what does that do for the Oreo?

EVELETH: Well, because the Oreos are so sweet, right? Like, you’ve got the chocolate cookie and then you’ve got that, like, really saccharin middle chemical bit—like, I don’t know what it is—

GRABER: The white part.

EVELETH: The white part—it’s so sweet that just a little bit of like spiciness or that little bit of, like, mustard flavor is really a good foil to the Oreo. It’s delicious. I know everyone listening is going to be, like, you’re a psychopath. But I love it.

GRABER: I totally want to try this.

EVELETH: It’s really good.

TWILLEY: I might skip mustard Oreos. But I’m much more into Rose’s most recent mustard revelation.

EVELETH: I have been really into making Bloody Marys recently, and I put a little bit of mustard in my Bloody Mary mix.

TWILLEY: Wait, the spread or the powder?

EVELETH: So I’ve been experimenting with both. So I will put a little bit of powder in the ring, like, the ring that you put on the glass.

TWILLEY: Oh yes, that does sound really good.

EVELETH: And then a tiny bit of it in. Yeah, it’s super good. You have to be careful because you could definitely overdo it with mustard powder particular. But I also put a little bit of Dijon in the actual sort of concoction, the tomato paste concoction that I used to make Bloody Marys. I’ll make you Bloody Marys any time, they’re my favorite drink and I’m really into making them.

GRABER: I’m so there!

TWILLEY: And that’s it for today’s episode because we have somewhere to be! There is a mustard Bloody Mary calling my name.


GRABER: Thanks this episode to Rose Eveleth. She is the host of a fascinating podcast called Flash Forward—it’s all about possible and not so possible futures. She had a recent one on a future where we’re all telepathic, and another scary and possible one about what happens if the census goes haywire.

TWILLEY: Thanks also to Patrick Edger of Michigan State University, Hayley Saul of Western Sydney University, and Madhur Jaffrey, legendary food writer and actress. We have links to their work on our website, gastropod.com. And, finally, thanks to Barry Levenson of the National Mustard Museum in Middleton, Wisconsin.

GRABER: We’ve got some more fascinating mustard stories involving mustard gas, mustard plasters, and mustard sounds saved for our special sustaining supporters newsletter: if you’re able to donate $9 a month on our website or $5 per episode on Patreon, you too could enjoy some more mustardy goodness!


GRABER: We’re back in two weeks with a few famous friends. Yep, we’re hanging with Nigella and Yotam and we’re name-dropping like we just don’t care!

Secrets of Sourdough: TRANSCRIPT

This is a transcript of the Gastropod episode Secrets of Sourdough, first released on December 19, 2017. It is provided as a courtesy and may contain errors.

CYNTHIA GRABER: That’s really good.

NICOLA TWILLEY: Really good. That’s good.

GRABER: One more—I know, I just need one more little bit.

TWILLEY: Just one more piece.

GRABER: I’ll join you in that.

TWILLEY: How can I not? It’s so good.

GRABER: It’s so warm and yummy. I’m going to taste some of this. Mmmm, Nicky—hot pita with garlic butter?

TWILLEY: Welcome to an episode of carb lovers anonymous!

GRABER: Not so anonymous. Nicky, they know who we are. I’m Cynthia Graber—

TWILLEY: And I’m Nicola Twilley, and this is actually Gastropod, the podcast that looks at food through the lens of science and history. And Cynthia and I are the not-so-anonymous carb lovers.

GRABER: We spent three days in Belgium with two scientists and more than a dozen bakers. We were in theory investigating a deep scientific question about bread—but actually

TWILLEY: We were eating our body weight in bread. And Belgian waffles.

GRABER: Nicky, I still am not sure I can forgive you for encouraging me to eat that second hot Liege waffle—I felt a little sick afterwards—but it was frigging amazing.

TWILLEY: Listeners, I ask you: was that a bad thing that I did? No. When in Belgium, eat the Liege waffles.

GRABER: But you’re not here to find out how many pieces and what types of bread we gorged ourselves on in a 72-hour period. You want to know what we wanted to know: all about sourdough. In fact, many of you have written us emails asking us to do this very episode. For instance, listener Alex Freedman, who lives nearby in Somerville but grew up in San Francisco, wanted to know about the history of sourdough. Alex, we’re on it.

TWILLEY: Listener Danae Garriga is northern Illinois requested an episode devoted to sourdough starters. As a baker, she’d read about wild yeasts and how the environment the starter is made in affects the microbes in it. And she wanted to know, if she gave some of her sourdough starter to a friend, would the microbes in that starter change? Danae: exciting news, that is exactly what we went to Belgium to figure out, in the world’s most delicious science experiment. In fact, we have the world exclusive scoop on this brand new research!

GRABER: It’s true, we tagged along with scientists at the cutting edge of sourdough. The question they were trying to answer is: those microbes that make up your wild sourdough starter, where do they come from?

TWILLEY: Is it from the water, like so many people—especially in San Francisco—believe? Is it from the baker or the bakery?

GRABER: Or is it from the flour?

TWILLEY: This was a gigantic scientific mystery. Up till now.

GRABER: We are going to take you along to Belgium with us on this path of scientific sourdough discovery. But a quick note, if you’re a regular listener, you know we have a Gastropod drinking game: we say microbes, you yell, “drink!” and then, you know, do so. If you do that this episode, you’ll be drunk. Really fast.



GRABER: This summer, Nicky and I traveled to a remote corner of Belgium. We were visiting the headquarters of Puratos, one of the world’s biggest bakery ingredients companies. They’d invited more than a dozen bakers from more than a dozen different countries to participate in a science experiment.

PAUL BARKER: Hi, my name’s Paul Barker and I’m from the U.K.

CHRISTOPH VÖCKING: My name is Christoph Vöcking, I’m from Germany.

JOSEY BAKER: My name is Josey Baker, and I’m from America.

STAVROS EVANGELOU: Hello, my name is Stavros, I speak English not good.

HAKAN DOGAN: I am Hakan, I’m from Turkey.

LETICIA VILCHIS: I am from Mexico. I am a baker too.

TWILLEY: And then there were also two scientists: Anne Madden and Rob Dunn. They work together in Rob’s lab at North Carolina State University. And they were meeting all these bakers for the first time too—to introduce the experiment.

ROB DUNN: We know that when you make a sourdough, the species and strains of microbes in that starter, they influence the nutrition of that bread, they influence the flavor of that bread. They influence every part of the bread. And yet it’s still pretty mysterious what determines which of those microbes are originally in your starter.

GRABER: Rob and Ann are microbiologists. They’ve been studying communities of microbes in all sorts of places—your bellybutton, your showerhead…

DUNN: And we’ve worked on microbes for a long time and often the responses is repulsion, like oh gross, there are microbes in my house.

ANNE MADDEN: When you talk to people about bacteria that might be in their bathroom it’s ugh, ugh, please stop talking, please don’t tell me any more. I don’t want to know. But when you talk to people about the microorganisms in their sourdough, it’s like, what did my children do? This is lovely. Like, can we put it on the refrigerator? Are there pictures? I love the response.

DUNN: And this was this one little niche where people seemed to gather around the idea that this was a beautiful kind of microbe, that there was something wondrous about them.

TWILLEY: And there really is something wondrous about a sourdough starter. It’s a community of wild microbes that somehow, miraculously, makes bread rise.

GRABER: And you need something to make the bread rise, because otherwise, if you mix flour and water and bake it together, you get matzah. Or, you know, a cracker. Hard and flat.

TWILLEY: Today, if I’m a baker and I want to make my bread rise, I can just go to the store and buy some baker’s yeast. Baker’s yeast is precisely one microbe, Saccharomyces cerevisiae, but it does the trick.

GRABER: But bakers have been making leavened bread in an oven—bread that puffed up and got soft like ours does today—people have been baking that for thousands of years. The ancient Egyptians made bread.

KARL DE SMEDT: So our question was okay, so where did the Egyptians bought their yeast? Because to make bread you need flour, water, salt, yeast. So where did they bought their yeast? They didn’t. It was there.

TWILLEY: This is Karl de Smedt. He’s the communications and training manager at Puratos, and, for this experiment, he was the one in charge of wrangling the bakers. And before we got started on the science, he dropped some sourdough history on the group.

GRABER: Nobody knows exactly where and when sourdough bread was first invented. The earliest evidence we have for making bread comes from a site in Africa. Archaeologists have dated the remains of that bread to about a hundred thousand years ago. It was probably made from pounded sorghum and water and baked on a hot stone.

TWILLEY: We’re not sure whether that was a sourdough or not—but it may have been something like the injera that Ethiopians still eat today. That’s sort of spongy and bubbly, and those bubbles are created by a community of wild microbes, just like today’s sourdough.

GRABER: Basically, if you combine ground up grains—something like wheat—with water, and you forget about it and leave it alone, eventually it starts bubbling. And that’s because a bunch of different microbes, usually a combination of fungi like yeast and bacteria like Lactobacillus, they colonize the mixture and feed on the flour and that is both the start of beer, and a sourdough starter!

TWILLEY: There’s hot debate among historians about whether humans first figured this out because they were making booze, or making bread. I am on team beer, to be honest, but short of Cynthia finally inventing her time machine, we will probably never know. Either way, humans figured that this wild bubbly mix made their flatbreads into breads—the non-flat kind. These loaves of bread would all have been sourdoughs. There was no other way to make bread rise.

DE SMEDT: So for thousands of years sourdough was being used by each and every baker or person that would bake bread.

GRABER: And even before people knew what microbes were, they were already caring for these wild communities of bubbling beige gloop, feeding them with more flour and water to keep them alive and happy. They figured out that you only need to add a dollop of starter to your dough to leaven it, which means you can keep the same starter going for years and years—decades even—just by feeding it with flour and water and using a little bit of it every time you bake. It becomes like your own personalized wild leavening mix that you can keep alive and use it again and again and again.

TWILLEY: Other people developed variations on this approach. In ancient Greece, for example, Pliny the Elder describes people saving a piece of their dough from the previous day to raise their bread the next day.

GRABER: Pliny also reported that people in Gaul and Iberia, otherwise known as France and Spain, they would use the foam they’d skimmed from beer to produce what he called “a lighter kind of bread than other peoples.” It’s the beer/bread question again—either way, it’s communities of microbes that grow on mashed-up grain-and-water mixes, and that have the power to both leaven bread and ferment sugar into alcohol.

TWILLEY: Over time, we figured out how to curate and stabilize these communities, so that they worked as expected, most of the time. Still, they were all a little different and a little finicky—my sour culture might make bread rise faster, yours might produce a better crumb, mine might all the sudden stop working.

GRABER: But these sour cultures were the only tool we had to bake leavened bread. And then everything changed.

DE SMEDT: And with the discovery of the microscope, with some research done by scientists, actually with Louis Pasteur, who wrote this Memoire sur la Fermentation Alcoolique, who opened actually the production of commercial baker’s yeast.

TWILLEY: It was two Hungarian born brothers, Charles and Max Fleischman, who first commercialized Pasteur’s insight. They started selling baker’s yeast—fresh yeast, sold in little cakes.

DE SMEDT: And it was such a convenient product that bakers embraced it with open arms. They all started to switch from that very inconsistent, complicated, long process that is sourdough towards something that is very precise, very accurate, very fast, very reliable, that’s called yeast. And so, in 150 years, bakers switched completely.

TWILLEY: Like I said, commercial baker’s yeast is just one microbe, not a community. Which has both pros and cons.

DUNN: So, commercial yeast is super boring, right. So nobody ever thought Saccharomyces cerevisiae, this baker’s yeast, was the most flavorful, that it had the best effect on the bread. We just thought you could make a ton of bread really quickly.

GRABER: Because not only is it a single yeast that you can buy whenever you need some, and that doesn’t need feeding or watering or loving care, but it also makes your dough rise a lot faster than that sourdough starter you’ve been keeping alive. By the 1960s, boring commercial baker’s yeast was available as shelf-stable granules in little packets. And, by then, bakers had also invented industrial processes that sped up the whole rising and baking process to just over three hours.

TWILLEY: This  bread—the bread of 1960s, the bread of our parents—this was not good bread. Karl says the 1960s was bread’s nadir. Sourdough all but disappeared.

GRABER: The 1960s sucked for bread, commercially. But it was also the time of good bread’s rebirth. The country’s first Zen Buddhist monastery was created in California in the late 60s. It was called Tassajara. The monks there baked bread slowly as part of their spirituality. They saw bread as being alive.

TWILLEY: And a young Zen student named Edward Espe Brown, who lived and worked at Tassajara—he published a book collecting the monks’ recipes in 1970. It was super homemade and hippie—the cover is made of brown paper, it was published in a tiny edition by Shambhala Press, and Edward received the princely sum of $100. But it sold out immediately, and went into second and third and fourth printings. Making your own sourdough bread at home became part of the counterculture—and a way to eat healthier.

GRABER: At the same time, there was another group of people who thought that commercial bread kind of tasted like crap. They weren’t inspired by spirituality or health, but by flavor. Between them, these two groups helped create the sourdough revolution.

TWILLEY: This revolution took a while to spread. During Karl’s own training as a baker, he never set eyes on a sourdough. It wasn’t till he started working at Puratos, in 1994, that he first encountered it.

DE SMEDT: I’d been to one of the better bakery schools in Belgium and we never learned how to make sourdough. It’s just not part of the educational program. So it was a discovery. I had to take out a bucket of the fridge. It looked strange. It smelled strange. It was funny when you touched it—it was a bit sticky.

GRABER: But Karl is thrilled to say things have been changing for sourdough.

DE SMEDT: And we see now, the latest 20—25 years there is a revival of sourdough and we think we are at the beginning of something very nice that will come in the coming years where sourdough will again take its place in the bakeries that it deserves.

TWILLEY: With that sourdough revival came a renewed appreciation for the diversity of microbes in sourdough starters—and they are diverse. As we discovered.

DE SMEDT: Come closer, come closer, because something very special is going to happen. You have to realize that what we have here is probably the most unique place in the bakery world.

GRABER: Karl led the group up the stairs and to a closed door.

DE SMEDT: Ready? Keep your eyes on the door, let’s go for some magic. Three, two, one…

BAKERS: Whoa! Ahhhh!

TWILLEY: And with that, we stepped inside the world’s one and only sourdough starter library.

GRABER: It’s a library, yes, but instead of bookshelves, there are 12 illuminated refrigerators with glass doors so you can see the jars inside. Karl’s collected 93 different sourdough starters from 17 different countries. And they look totally different from one another.

DE SMEDT: Some are liquid and some are stiff. And then some are very dark. Some are speckled. Some are almost looking like crumble, because they’re so dry. So there’s a lot of colors—dark to brownish to yellow, and then the normal white ones.

TWILLEY: Karl took some of the jars out and allowed us to smell the starters. Some smelled fruity, some were acidic, some were biscuity, some were creamy.

DE SMEDT: The Chinese, for example, one of them is very meaty. When I open the jar, it’s like almost a sausage, very savory. Some are really very pungent, when I open the jar and smell, you really feel the acids go into your nose, and it’s like if you were to have a spoon of very heavy mustard, the Dijon mustard—that reaction.

GRABER: Karl’s goal with this collection is to preserve the communities of microbes that make each sourdough unique. But for Karl, it’s also really fun.

TWILLEY: Karl is the keeper of the sourdough library. He can’t sell these starters or even give them away. Each unique microbial community still belongs to the baker who donated that starter in the first place. But Karl feeds them and takes care of them. And sometimes he plays with them, too.

DE SMEDT: I do take home some sourdoughs and I do some experiements and, yes, I do bake with them. And I discover some other things. Sometimes the fermentation power is totally different.

TWILLEY: When Karl is feeding the starters he puts them in small plastic buckets.

DE SMEDT: Some of them they just blow away the lid of these things. And other ones are just very, very slowly rising, fermenting. So there’s really differences in fermentation power, in flavor, in aroma, in the way the dough is feeling when you touch the dough, it’s different. So yeah.

GRABER: Karl’s point is that these starters are all different from one another. And the library itself is also unique. Nobody’s ever tried to conserve communities of useful food microbes for the future.

TWILLEY: Walking around the library, looking at these spotlit jars in their glass refrigerator vitrines, you really see each sourdough starter as a distinct, individual, precious thing. But how different are they microbially, really? Who’s living in those jars?

DUNN: Sourdough, in terms of the number of species we know how to grow, is toward the simple end. Often you’ll have two to four culturable bacteria species and one yeast species. It’s very likely, although we don’t know, that there are also things that are hard to culture in the lab that are in those sourdoughs, that make it a little bit more complex. But it’s toward the simpler end in terms of numbers of species. It’s not simple though in as much as different sourdoughs seem very different. And so if you were to look around the world, how many different species could you find in all of the sourdoughs? That’s actually a much longer list. And so an individual sourdough: simpler. This big picture of sourdough is far more complex.

GRABER: As Rob is explaining, a sourdough starter is an interesting creature, or, really, creatures. You can have a community of just a handful of different microbes that works perfectly together—as Rob says, maybe two to four species of bacteria, maybe one kind of yeast, and it’ll work. It’ll make sourdough.

TWILLEY: But what’s also probably true is that your sourdough starter could contain an entirely different community than mine, and they’d both still make sourdough. And it’s that diversity—that huge world of bacteria and fungi that can collaborate to raise bread—that’s what Karl is trying to collect.

GRABER: His library, as unique and impressive as it is, is probably just the tip of the iceberg. And maintaining this library is a lot of work—it’s not just collecting samples and putting them behind glass.

TWILLEY: Any baker can tell you what a commitment it is to keep a sourdough starter alive.

BARKER: I always describe it, if you have a sour culture, it’s like having a pet or a child, yeah?

GRABER: Paul Barker owns a bakery just outside London called Cinnamon Square. And he has many sourdough pets.

BARKER: You have to look after it. If you don’t feed it, keep it warm, or whatever. So unless you look after it, it will spoil, it will eventually die on you. So it’s a commitment to having a sour culture .

TWILLEY: In fact, there are even specialized sourdough hotels, where you can send your sourdough starter to be looked after if you’re going on a super long trip. A sourdough starter is really much higher maintenance than commercial yeast, so why do bakers use it? We asked Paul.

BARKER: Firstly, because the sourdough gives you a much different type of bread: different textures, more digestible bread, more nutritional breads. So I like the fact that you can get a totally different product. And you can be so creative with a sourdough, more so than a yeasted bread. So you can actually do a lot more with the shape in the baking, the decorations, I think—because you can get more from it whereas a yeasted bread, a commercially yeasted bread, you are just expanding your dough and baking it.

GRABER: Commercial yeast, as Paul explained—it makes the bread puff up, but that’s it. Paul knows that the microbes in his starter are giving him a different dough. It often has the right type of texture to allow him to play around more with the shape of his loaves. But what are those microbes actually doing to create these differences, and how are they doing it?

DUNN: So the microbes in the starter are starting to break down some of the hard-to-break-down things in the grain that you’ve given them to eat. And they are beginning to produce these gases that we think of as some of the really important flavors in the bread. But, as they metabolize the grains, they’re also also altering the structure of the carbohydrates that are present, which then is going to alter the nutrition of the carbohydrates, it’s going to alter the outside of the bread.

TWILLEY: As Paul has noticed and as Rob just explained, microbes improve the texture and the nutrition and even the look of the final loaf. They can even produce extra vitamins. But they also shape its final flavor—you can literally taste the difference between bread from different starter communities.

DUNN: And so butteriness—a lot of butteriness comes from which microbes are in your starter. The kind of sourness you have—how lactic it is versus how acetic it is—that comes from which microbes are in the starter.

TWILLEY: Rob told us that some sourdough bread has a particular gooey, melt-in-your-mouth feel that comes from a chemical called dextran, which is produced by a bacteria called Weissella. Weissella lives in some sourdough starters, but not in others.

GRABER: So: microbes are munching away on the flour, excreting things like buttery flavored lactic acid and yeasty farts that puff up bread. That much we know. But Rob and his fellow microbiologists don’t understand how all this microbial munching and excreting creates the differences between different finished loaves of sourdough.

DUNN: And the further you get down that chain of events, the less we understand about the mechanics of how all of that is happening. But what we do know is that all of the things that could influence those final flavors, final texture, final nutrition are things that we think of as predominantly microbial.

TWILLEY: So we don’t know. We really don’t know how the microbes are working their magic. We don’t even where they come from in the first place. But Rob wants to know. And so did we. And hence this giant 3-day experiment in Belgium. Which we have the exclusive first results from after the break.


TWILLEY: Back to Belgium. Where we are about to conduct an epic baking experiment in order to figure where the microbes that are in a sourdough starter actually come from in the first place.

DUNN: So, in order to make a starter, you take a simple set of ingredients and you expose them to open air and to your body and to your home, and it starts to grow. It’s like making a garden without ever planting the actual seeds. The mystery to me is: what determines which life forms are growing in that garden? And so that’s the fundamental mystery: why is your garden different from my garden when we use the same things to start with?

GRABER: Many bakers think they know the answer to this mystery.

VILCHIS: I think is flour. But the hands of the bakery is very important too to the results.

BAKER: I think it’s probably a combination of all of the variables.

MARCUS MARIATHAS: It’s mostly, in my opinion, the reaction within the flour and water. That’s where it starts.

BARKER: I would assume the environment is going to play a part in it as well. Because it’s going to be a lot of cross contamination in bakery from different flours anyway and you can end up with different types of sours.

MADDEN: I feel like every baker we talk to has a different assertion about where the microorganisms from that sourdough starter came from. Some people are very clear: it’s likely coming from the flour. If I use a different flour, I’ll have a different sourdough starter and a different sourdough starter must be different microorganisms. Some people have suggested that it’s the water. That’s why San Francisco sourdough is San Francisco sourdough and you can never make it in New York. There are claims about it being in the wood of buildings.

DUNN: What I like about this project is that as scientists we have not had to come up with our hypotheses because the community of sourdough makers has provided us with the longest possible list of what they might be.

TWILLEY: From that long list there are four main hypotheses: that the microbes that make each sourdough starter unique and individual come from (a) the wheat, (b) the water, (c) the environment, and (d) the baker themselves.

GRABER: Rob says we know that there are different microbes on different grains. Even within the same grain, there are different microbes on different strains of wheat—different heritage varieties, for example. Or wheat that is grown in different ways, like organic wheat. And then, even on the same plant, you can find different microbes in the germ of the grain versus the endosperm. The endosperm is what millers use to make white flour. So this means that whole wheat flour has different microbes than white flour does. Rob says these all these variables in the flour itself could certainly be influencing the sourdough starters.

TWILLEY: Then there’s the hypothesis (b), the water.

DUNN: Water can conceivably kill things in the starter. It’s unlikely to be adding things to the starter because we have a pretty good list of what lives in water. I think people are surprised often that all water they ever drink, even bottled water, has microbes in it, but they’re not the kinds of microbes we characteristically see in sourdough.

TWILLEY: In other words, Rob is saying that the water might prune particular microbes out of a sourdough starter garden, but it’s unlikely to be contributing any new microbes itself.

DUNN: The other thing though that that can then contribute to the starter is what falls from the air into the starter.

GRABER: This is hypothesis (c), the environment around you as you make the starter. Rob says that plants might have a particularly strong impact, because of the insects they attract and the microbes on those insects.

TWILLEY: And then there’s just the bacteria that are swirling around in the dust and air. Some of those come from pets, if you have pets. The majority of them, usually, come from your own skin and the skin of the people you live with.

GRABER: And finally, hypothesis (d), the baker.

TWILLEY: Specifically, the microbes living on the baker’s skin.

DUNN: We can think of many ways that microbes differ from one person to another person.

TWILLEY: For example, there’s that gene that determines whether you have sticky or dry earwax.

DUNN: And depending on which version of that gene you have, your skin microbes in your armpits, but also around your body more generally, are super different.

GRABER: There are also microbes on your skin that don’t live on your skin. They get there when you touch parts of your body that have other microbial communities. Like your gut microbes.

DUNN: And then we know that human women and human men differ greatly in microbes because of vaginal microbes. And so women have way more Lactobacillus in general, but especially in vaginal communities, and those sort of travel around through the day-to-day business of being a human.

TWILLEY: These vaginal microbes are particularly interesting because Lactobacillus is a key part of most sourdough starter communities.

DUNN: Yes. So, in some cultures, sourdough is mostly or exclusively something that women bake. And to me it’s really intriguing to think about does that have something to do about the unique sourdough community that emerges when women make sourdough versus when men make sourdough.

GRABER: This three-day Belgium adventure, the experiment we’re watching unfold—it’s designed to try to tease out where the microbes in the sourdough come from. A, B, C, or D.

TWILLEY: To be precise, it’s designed to isolate two variables from these four possible sources for the microbes in sourdough—the microbes on the different baker’s hands and in their environment. Those are the variables.

MADDEN: They were shipped the ingredients, they were given the same protocol, the same recipe.

GRABER: That is, these bakers were shipped exactly the same flour. Not the water, because based on the existing research, Anne and Rob don’t think the microbes in water plays a big role.

TWILLEY: Anne and Rob cultured the microbes out of that flour, so they already have a list of the microbes that are being contributed to the starter from the wheat.

GRABER: Like Anne said, the bakers were given very specific instructions about exactly how much flour and water to use and exactly how long to ferment their starters. The goal is to make this all as controlled as possible.

TWILLEY: So all these bakers, men and women, in different parts of the world, they all made their sourdough starter using the same flour according the same protocol. And then they put their starters in a baggie and they brought it with them to Belgium

MADDEN: And that was a really fun part, when we got to open them all up and they’re coming in and some of them smell like vinegar and some of them smell more like yogurt and some of them smell creamy.

GRABER: As soon as the bakers arrived, Anne and Rob opened packages of sterile swabs, like super long Q-tips, to get samples of those rich microbial communities in the starters.

MADDEN: Just one double swab per.

GRABER: Then we took a break from the science. We all introduced ourselves and met each other, and everyone talked bread.

TWILLEY: The final part of the experiment that day was refreshing the starters, according to the protocol.

BAKER: I’m going to put my starter in this bowl, first of all dilute it with the water, and then add the flour on top, mix it, put it back in here, and then we’ll wait until tomorrow.

GRABER: And that’s it?

BAKER: And that’s it.

TWILLEY: And then we all ate dinner together accompanied by lots of bread, and day 1 of the experiment was over.

GRABER: First up day 2? After breakfast featuring lots of bread, we got to everyone’s not-so-favorite part—getting swabbed to find out what microbes live on their skin.

TWILLEY: Paul from London was up first.

MADDEN: Now, I’m going to be swabbing your hands, and I’m going to ask that put your hands out just in a way that I can apply some pressure. And I’m going to spend a few seconds.


MADDEN: Just going over the front and then I’m going to ask you to flip and then I’ll do the back. And if we could not talk over the swab when it’s out so that we can not introduce some of our oral microbes.


MADDEN: Thank you.

TWILLEY: Anne was swabbing the baker’s hands because if any microbes are going from a baker’s body into their sourdough starter, they are probably getting in there via their hands.

DUNN: You know it will be wonderful in some future version to you know top-to-bottom swab all these bakers and really start to tease out, you know, which body part is really contributing. But we had to start somewhere and so we started with the hand connection.

GRABER: In case you’re getting a little grossed out, don’t worry. The bakers do wash their hands. And they should wash their hands. Anne made sure to emphasize that. Even after you wash your hands though, there are still microbes on them. They’re everywhere.

TWILLEY: So, next step: after their hands were swabbed, the bakers were allowed back into the test kitchen to be reunited with their starters. Which they could hardly wait. It was like parents at the kindergarten gate. But before they could be fully reunited, the starters all had to be tested with some cool science gear, to find out their pH and their organic acid content.

TWILLEY: Once again, the sourdough starters all looked—and smelled—completely different.

KASPER HANSEN: My sourdough is called Danish Dynamite.

GRABER: That’s right, Danish Dynamite.

CASPER: So a lot of activity inside. So, as you can see, up side of the glass here.

TWILLEY: It was like looking at baby photos, I’m not kidding. Everyone thought theirs was the prettiest of all.

GRABER: You’re smelling your sourdough?

TOMMASO RIZZO: Smell is buttermilk—smell, taste, aroma.

GRABER: Can I smell? Mmm, yeah, it’s got a little sweet. The bakers made their bread and left it to proof overnight. And, as that official science-experiment bread was rising, the bakers were set free in the test kitchen to let their pent-up creativity run wild.

TWILLEY: And they went to town. Hakan made this crazy Turkish bread that had lots of melted cheese and a cracked egg on it. Leticia, the Mexican baker, she was putting cocoa and raisins into a sourdough loaf. Someone made pita bread.

GRABER: I’m going to taste some of this. Mmm. Nicky, hot pita with garlic butter? It’s really good.

TWILLEY: It’s really good. That’s good. So look, let me do this.

GRABER: Mmm, the smell.

TWILLEY: I’m squeezing the bread like it’s a bellows on an accordion or something. Or trying to light a fire. This is what I’m doing.

GRABER: That smells amazing. It’s like as you squeeze the dough the scents in the air pockets just, like, get blown right at your face.

TWILLEY: So I stood here. Stavros, like, pumped the bread in my nose, and Vassilis was like “This is sourdough.” We sniffed bread and we ate bread, and then we ate more bread.

GRABER: And then we ate dinner. Which also had some bread.

TWILLEY: And then we rose bright and early on the third day, had some bread for breakfast, and went back into the kitchen to bake the science-experiment bread. But… there was some tension.

GRABER: Tommaso, for one—he’s from Italy—he didn’t want to put his bread in the oven when everyone was told it was oven time. He said the dough wasn’t ready for baking—it hadn’t risen enough. Rob whispered to us that he and Anne were having a hard time making sure that all the bakers kept to the scientific protocol.

DUNN: Yeah. So we’re thinking about it right now. There’s a tension between what people view as counting as a bread. And, uh, what we want.

TWILLEY: Tommaso was overruled. In the nicest possible way. And all the bakers’ dough went in the oven at the same time. And the same way that their starters had looked and smelled really different, despite having been made from the same flour using the same instructions, the dough looked really different as it went into the oven, too.

GRABER: You could see some really big air bubbles in some and none in others. Some rose a third of the way up to the tops of the baskets, some rose all the way to the top. Some were super bubbly on top, some were shiny and smooth. And then the bread came out of the oven.

GRABER: Oh. Those are pretty. (OVEN DOOR CLOSING)

TWILLEY: Some of the bakers were happy and some were not. So these are Tom’s, you like the look of them?

WALTER: I like them. Because when it’s cracking open, you see black line. And Karl calls it eyeliner—so we have to bake it so—eyeliner on the bread.

TWILLEY: And eyeliner is a good thing, right?

WALTER: Yeah, yeah.

GRABER: I learned something new—I never knew bread should have eyeliner on it. It’s basically the nice, dark, cracked edge you see at the top of the loaf. Tom’s loaf had really lovely eyeliner.

TWILLEY: This has a lot of nice fish eyes or blisters.

GRABER: Little bubbly blisters on the cooked crust are another sign of a great sourdough. But some loaves didn’t look as good. Like Paul’s. And this one doesn’t look like it did very much over here, it didn’t even crack.

TWILLEY: Which are yours?

BARKER: The ones that are looking very sad at the back. The two behind this one here.

GRABER: No, they’re not very…


TWILLEY: And then, as soon as it was cool enough, all of the loaves were sliced in giant bread-slicing machines. And the bakers were asked to evaluate a slice from each loaf. They had to assess its appearance, its smell, and, of course, the way it tasted.

TOM REES: So we’ve got kind of two different colors, I see already. One which is a bit grayer, and one which is a bit more yellowy, creamy color.

TWILLEY: And is that reflected in differences of smell too?

REES: Yeah, so the greyer ones—the greyer ones have less of an acidic aroma

BARKER: Some are creamy and some have gone kind of more reddy, kind of browny, sort of hints. So there was a distinct difference in the color, which is quite interesting. I wouldn’t have expected that considering we are all using the same flour, the same ratios of ingredients.

BAKER: Like the one of Guillermo is dense and stronger, and from Tom, it’s very fragile and very open. But the taste and smell is about the same.

VILCHIS: For example, Hakan is very very similar to Kasper. I think is the same bread. Incredible. Paul is the same than Guillermo.

HANSEN: It’s much more like wheat—not so fruity. Hakan and Tom, taste more—have more acid taste.

DUNN: And so in this case we know that all those differences from bread to bread are really microbial.

GRABER: But it might not actually be because the starter contained different microbes. The exact same microbes can create different smells and tastes just based on the temperature that they grow in, for instance. So these results, that the breads smell and taste different? Could just be because the temperature in London is different from Guadalajara.

TWILLEY: Sensory evaluation was not enough to answer this question. Instead, Rob and Anne had to take to their swab samples back to the lab and analye them.

GRABER: A few months later, we called Rob up to find out how it all went. (PHONE RINGING) Hey Rob! So Belgium ended. You packed up to go home. How did you feel?

DUNN: I felt super full.

GRABER: I felt really full, too, just so you know.

TWILLEY: I was never going to eat bread again. And then I did.

DUNN: No, I’m ready for more bread to be honest. There’s been time.

TWILLEY: Science takes time, but this science took a little bit longer than Rob wanted because his samples—the swabs from the bakers’ hands and the sourdoughs starters—they got held hostage in Belgium. Trying to get these kinds of biological materials across borders can be tricky. Rob is a patient man, but even he was getting a little frustrated.

DUNN: And then, amazingly, just last week, we got the first results from that decoding of DNA.

GRABER: Rob, Anne, and their whole team spent a day just marveling at the data and poking around. They were trying to figure out if they could make any sense of the data just by looking at it. Which, of course, they couldn’t.

DUNN: But then eventually we started to formally analyze what’s going on with the patterns of the data and that’s where it starts to get interesting. And so the first one of those analyses happened on Friday and the second one happened about two hours ago.

TWILLEY: So tell us! What did you find?

DUNN: Well, the first thing last week was a result we weren’t looking for, we didn’t anticipate. And I had no idea it was even possible.

GRABER: It’s about the bakers’ hands. Normal hands usually have Staphylococcus, and some armpit microbes, some bacteria that are the same as acne bacteria, maybe some random bacteria from things you’ve touched recently.

DUNN: When we looked at the bakers’ hands, their skin bacteria on their hands was about half sourdough bacteria. And so they, like, have sourdough paws.

TWILLEY: Sourdough paws!

DUNN: We’ve looked at zillions of hands. We’ve never seen anything like this. And so the first result is that the bakers themselves have changed in response to their occupation.

TWILLEY: Normal hands like mine and Cynthia’s and Rob’s—they are something like 2 to 4 percent Lactobacillus.

DUNN: On the hands of the bakers, it is like it’s the star of the show. It’s wild. I mean, if it’s right, you should be able to put flour and water on a baker’s hand and it should start to ferment immediately and become acidic.

GRABER: Working with sourdough has entirely changed the microbial environment on the bakers’ skin. They’ve been colonized by their pets! Rob wonders if the bakers spend so much time with their hands in acidic dough that the sourdough Lactobacillus microbes end up with a competitive advantage over normal skin microbes.

TWILLEY: So that is weird. But it’s not what Rob and Anne set out to find. What they were trying to understand from this 3-day Belgian breadfest is whether the microbes in the sourdough starter come from bakers’ hands—not whether bakers’ hands are somehow different from normal hands.

DUNN: So what we saw two hours’ ago was that there’s a group of bakers that has very different sourdoughs, and the unusual microbes in those sourdoughs are also on their hands.

GRABER: One question answered. The bakers who have weird bacteria on their hand have the same weird bacteria in their sourdough. There is a connection. Individual bakers do indeed seem to influence their starters. But so, does this difference influence the flavor of the resulting bread? Rob doesn’t know, he hasn’t done that research yet, but he has a hunch.

DUNN: I predict that second group has more unusual flavors. And we should be able to capture that. We’ll see.

TWILLEY: Stay tuned. Meanwhile, what Rob and Anne have done is sit down and compare the list of microbes that were in the flour and the list of microbes that were on the hands and the list of microbes that were in the starters.

DUNN: We get a total of about 193 kinds of bacteria in the sourdoughs. which is a lot more than the bakers tend to think is there, which is interesting in and of itself. Something like 80 of those are also found on hands. And roughly the same number seems to be found in the flour. And there’s overlap between the flour and the hands. We saw almost nothing in the water, so they’re probably not coming from the water.

TWILLEY: But they did see some microbes that weren’t accounted for, that were not from the hands or the flour. They were maybe microbes that were just floating around in an individual baker’s kitchen.

DUNN: Yeah, they could come from a leaf outside the bakery. It could come from a bowl or a spoon. But it’s not so surprising that we haven’t found where all those microbes are coming from—and, in some ways, that leaves the bakers some magic. Where does the stuff we’ve not measured yet coming from? Just magic. You guys can keep that.

GRABER: Rob also told us another new finding that totally contradicts what he told us back in Belgium, earlier this episode. Remember how he said that sourdough starters have three or four species of bacteria and maybe one species of yeast? Rob says based on these new samples he’s seeing ten species of bacteria in the average sourdough starter and maybe three species of yeast.

DUNN: We now have enough data to say that I was wrong when I was describing the simplicity of the starters. Which also means the whole literature is wrong.

TWILLEY: Folks, this is science in action. We think we know things, like about how many species of microbes live in a sourdough starter, and then we do some research and discover we don’t. But Rob pointed out that sourdough starters are still not particularly complex in microbe terms.

DUNN: And so part of the story that’s super fascinating to me is, you put out flour and water, all around the world, and somehow you can create a very similar ecosystem out of what for bacteria and fungi is a relatively small number of species. If you put out sterile soil in this many sites globally, you’d be looking at 20,000 species. And so, on the one hand, the individual starters are more diverse than we tend to think. On the other hand, that global picture is actually a lot simpler. So that was really interesting.

GRABER: Rob and Anne and their collaborators have really only just begun analyzing this data. Over the next six months, they’re going to be figuring out what types of compounds each species of bacteria can produce—not necessarily that they’re actually making those compounds in the starters, but that they can.

TWILLEY: And then they’re going to match those compounds to their possible effects in bread—different flavors, different textures, different nutritional values.

DUNN: The other part is we’ve barely touched the fungal data. And so that will mean we’ll be spending a fair amount of time on that even this coming week.

TWILLEY: So there’s much still to be done with just the data from our Great Belgian Bake Off. But there’s also just more sourdough research to be done in general. Our Belgian breadfest was only one of the sourdough experiments Rob and Anne have got going on the lab right now.

GRABER: They’ve already gotten about a thousand people from around the world to send in their sourdough starters. Rob and Anne want to get a big picture of sourdough diversity. They’re hoping to see patterns, like whether some species are more common in some areas of the world. And they’re already starting to see some results.

TWILLEY: Rob told us that, in terms of bacteria, there seems to be a shared sort of pool that colonizes grain and water mixtures all around the globe. In other words, the same bacteria are pretty much everywhere and then which end up in which starter seems to depend mostly on the flour and the baker, as we just learned.

GRABER: But they are seeing a little bit of geographic variation with bacteria. Some bacteria tend to live in more northerly Scandinvanian countries, for instance. That’s not the only anomaly.

DUNN: There’s a little bit of a hint so far that maybe France is kind of special.

GRABER: France is special.

DUNN: But the fungi we’re seeing globally have a lot of geography. And so there’s one one kind of yeast—a kind of fungus—that we’ve basically only seen in Australian starters. We know that the yeast can do a lot in terms of flavors and aromas. If that unusual yeast is playing a big role, then there could be a flavor that you could only actually savor when you’re in Australia. And we don’t know that yet. That’s a fun idea.

TWILLEY: Sourdough tourism is going to become a thing, just wait and see.

GRABER: One of the things Rob and Anne are going to do over the next year is bake some bread from these thousand starters that they received. That way they can start to assess flavor while controlling for the other ingredients. The ultimate goal is to arrive at microbial recipes for sourdough deliciousness.

DUNN: Once we do that, that will be the hope—that there is some mix that really gives you the perfect butteriness or the sourest souriness. Is souriness a word? I don’t know.

GRABER: Rob and Anne are also working with colleagues to tease out the evolutionary history of sourdough. They’re going to be working out how microbes in starters change over time. So, eventually, they’ll be able to tell you, if you’re using your great-grandma’s starter, are those your great-grandma’s microbes? Or, as listener Danae asked, if she gives her sourdough starter to a friend, will it change—and if does, how quickly?

TWILLEY: So there’s still tons to figure out about sourdough, but Rob is on it. And we’ll keep you posted as his results come in. It’s super exciting research. Not just because we love microbes.

GRABER: A round of applause if you haven’t keeled over yet from taking a shot every time we say microbes!

TWILLEY: We do love microbes, But we also love this research because it points the way to a future of even more delicious bread!

MADDEN: And so I think the question is the next step, which is: What microorganisms create what flavors and aromas and traits in bread that we want. And then we can start tracking down what microorganisms might be leading to those traits. And so you can imagine a future where you could think about the kind of bread you want. Maybe I want it to be crusty and kind of chewy with fruity notes. And by having that choice of bread, there’ll be a list of species that will work together to create that. So you’ll have a designer sourdough.


TWILLEY: Thanks this episode to the Burroughs Wellcome Fund for supporting our reporting on biomedical research.

GRABER: Thanks also to some of our Supreme Fan level Patreon supporters: Andy Allen, Lori Schultz, Justin So, Robert Wells, Alex Sol Watts, Eric Schmidt, Corinne Lewis, David Kohn, Matt Rooney. We cannot thank you enough for your generosity in helping keep Gastropod going.

TWILLEY: And a big thank you to Puratos, who hosted this experiment but also hosted Cynthia and me in Belgium. We have photos and links to Karl’s magical Sourdough Library on our website, gastropod.com

GRABER: Thanks so much to Rob Dunn and Anne Madden for letting us follow them around for three days and try not to get in the way of all their swabs.

TWILLEY: And thanks also to the lovely bakers, who couldn’t have been more of a fun group to hang out with while doing some cutting-edge science. And some competitive-level eating.

GRABER: We are going on a brief break over the holidays. But we’ll back in 2018. We have an amazing season lined up for you. If you’re on our sustaining supporters list, you’ll get a sneak peak at what’s coming up. Thanks to all of you who listen, who support the show, who write in, who take part in our Shareathon—we do this for you, and we couldn’t do it without you!
crumbs to try to identify their microbes. Could those microbes be the same as the ones in sourdough today?


Cannibalism: From Calories to Kuru TRANSCRIPT

This is a transcript of the Gastropod episode Cannibalism: From Calories to Kuru, first released on October 24, 2017. It is provided as a courtesy and may contain errors.


TWILLEY: So if you know this famous clip from “The Silence of the Lambs,” you will know that this episode, we could be discussing one of three things. Chianti. Fava beans. Or…

GRABER: Oh how I wish we were discussing chianti or fava beans. But no, this episode, we’re all about cannibalism. Happy Halloween!

TWILLEY: But, honestly, although we began with Hannibal Lecter, this episode is really not a gore-fest. This is, after all, Gastropod, where we look at the science and history of food. And the science and history of cannibalism turns out to be fascinating. I’m Nicola Twilley, by the way, the one who is not in danger of fainting this episode.

GRABER: And I’m Cynthia Graber, the one who has never seen “The Silence of the Lambs” because I am far too squeamish. But there’s interesting stuff here. We’ve all seen those nature documentaries where the spider consumes its mate after sex, but really, how common is cannibalism in the animal world? And why does it happen?

TWILLEY: And how common is it among humans, in the past and still today? All that, plus a caloric breakdown of the human body, for those of you who want to turn cannibal but are watching your weight.



GRABER: There’s one thing I wondered when we first decided to do this episode, and it’s the question I just asked. Really, how common is cannibalism in other species? It’s such a taboo among humans. Is there a biological reason eating each other would be disgusting for other animals, too?

TWILLEY: To find out, we called up Bill Schutt, who is the author of a new book called Cannibalism: A Perfectly Natural History.

BILL SCHUTT: Well, it’s really common. And that was a surprise to me. I’m a zoologist but I was not a cannibalism expert.

TWILLEY: Bill told us that up till quite recently, most zoologists, including him, thought that cannibalism was pretty rare, in all species.

SCHUTT: Except for a couple of strange creatures like praying mantises and black widow spiders, the party line was basically that if you saw cannibalism in nature it was because of a lack of nutrition or cramped captive conditions. If you took a bunch of animals and stuck them in a small tank or a cage then all bets were off, they would cannibalize each other. But over the last thirty years or so, scientists began to find out individually and then they—somebody finally put this together—that cannibalism takes place for tons of reasons that are quite natural and have nothing to do with with running out of food.

GRABER: So it’s common, or at least more common than scientists thought, but there are some really good biological reasons why you might not want to eat members of your own family.

SCHUTT: And one of them has to do with with something called inclusive fitness, which is pretty much a measure of how many genes you have in a population, and if you’re killing and consuming your own kin you are really decreasing your inclusive fitness. And the other is because there are species-specific parasites and diseases that can be transmitted.

TWILLEY: And yet, like Bill Schutt said, there’s a whole lot of cannibalism going on. Particularly at the squishier end of the spectrum.

SCHUTT: If you look across the entire animal kingdom, in the invertebrates, in insects and in spiders and in snails and things, cannibalism is quite common.


GRABER: Spider sex. You know it. The male approaches the female cautiously—after all, he doesn’t want to get eaten BEFORE he manages to get the act done.

TWILLEY: And she’s usually twice his size, total dominatrix.

GRABER: In the Australian redback…

TWILLEY: Where the guy is only a fifth of the size…

GRABER: The female rewards the male for having done his duty by vomiting her stomach juices onto the tiny creature hanging onto her to start pre-digesting him. Yum.

TWILLEY: Amazingly, he still comes back for round two at this point, even as he is being liquified. Praying mantis males keep going even after the lady mantis has eaten their head. But why? I mean, sex is great, but not that great, surely?

GRABER: It might seem like there there’s nothing in it for these poor guys other than those few moments of bliss. But scientists have found a number of reasons why sex cannibalism makes sense. The redback spider ladies will resist come-ons from other males if they’ve cannibalized their first suitor. So that cannibalized male’s sperm is the one that wins.

TWILLEY: Plus, counterintuitively, cannibalized males seem to go at it for longer and thus deposit more sperm and thus father more baby spiders. I suppose there’s a kind of desperation born out of being coated in stomach juices.

GRABER: Sexual cannibalism has been reported in 16 out of 109 spider families. So not all spider sex is deadly, but it’s definitely going on. Okay, that’s enough sex cannibalism for the moment. Now onto why parents would eat their babies.

TWILLEY: In this particular niche form of cannibalism, fish are the undisputed leaders. According to Bill, ichthyologists consider the absence of cannibalism in a fish species to be the anomaly.

GRABER: Picture the open ocean. In order to make babies, the female releases a cloud of eggs, maybe millions, and the males release clouds of sperm. Only some make it to become baby fish, but there’s all those calories available in the water. Bill says the eggs look to fish just like a handful of raisins might to us. Why not eat them? So they do.

TWILLEY: And finally—keeping it in the family here—oftentimes the kids eat other, too. This is a strategy Bill’s seen a lot in birds.

SCHUTT: Cannibalism as a lifeboat strategy where you’ve got say, a couple of nestlings and they’re born asynchronously. So one is going to be larger than the other. And if there’s enough food to go around then fine but if not then the smaller nestling will sometimes get cannibalized.

GRABER: Survival of the fittest. It’s bird-eat-bird out there. Sometimes this juvenile cannibalism is just training for the real world.

SCHUTT: Then there are these sand tiger sharks, where the eggs hatch internally. And there are eggs of different ages. So the oldest on each side of the reproductive tract, once they use up their yolk, will start to eat the eggs and once the eggs are gone they’ll eat their brethren. Smaller and and quite nutritious. So when they’re born, there are only two of them. And in a sense they’ve been trained to be predators while still inside their mothers.

TWILLEY: Natural-born killers indeed.

GRABER: By the time you get to mammals, scientists have only found cannibalism in 75 out of 5700 species. It’s much more rare.

TWILLEY: But it happens, and for much the same reasons: survival, basically. When animals are hungry, sometimes they’ll scavenge off their dead relatives. So they’re not killing them for food, but you know, if they’re dead already, why not?

GRABER: Sometimes if animals are living in a crowded and stressful environment, they start to see their neighbors as food. And then there’s protecting your own genetic line. You want your babies to be the ones that live.

SCHUTT: So, for example, if you are a lion and you take over a pride and there are females who have cubs from other males, you kill and sometimes eat those young. And so you are really terminating the maternal investment in those young so that the females come into estrus quicker and then you can mate with them if you’re the male who took over.

TWILLEY: So bugs are eating bugs, fish are eating fish, some mammals are eating other mammals. But surely among our close relatives, this sort of behavior isn’t going on?

GRABER: It’s rare, but it does exist. Bill says that in primates, cannibalism has been seen only in 11 out of 418 species. Not a lot. It’s usually stress related, or it’s about aggression, like when males patrolling their community come across neighboring male patrols. Like other soldiers.

TWILLEY: OK, that’s primates. Who’s next? That’s right, brace yourself, Cynthia. It’s time to talk about human cannibalism.

GRABER: I’m working on it. Okay, turns out, there’s quite a bit of archaeological evidence of cannibalism among early humans.

JAMES COLE: So the oldest is Gran Dolina, which is a site in Spain. And it’s dated to about 936,000 years ago, to a species called Homo antecessor. And what we see there is a small group of people, so two adults, three adolescents, and six children, that seem to have been butchered and eaten by another group of Homo antecessor who were living in that region.

TWILLEY: Meet James Cole, he’s principal lecturer in archaeology at the University of Brighton in England. And he’s studied cannibalism in prehistoric times, when there were a bunch of different human species, not just Homo sapiens.

COLE: And certainly if you look at human evolution, well, difficult to say really if all human species conducted cannibalism but certainly a lot of them did. So it seems to have been a regular part of our behavioral development for many millions of years.

GRABER: It might seem to be common, but how do we know for sure? What kind of evidence can you find from almost a million years ago?

SCHUTT: If you really want to prove that cannibalism took place you’d need to find a coprolite, a fossilized fecal pellet, and then be able to show that there was for example human DNA or human hemoglobin or myoglobin inside that—those feces.

TWILLEY: And we haven’t found that. But without the smoking gun of a fossilized turd, how exactly is James so sure that our prehistoric fellow men were eating each other?

GRABER: Well, archaeologists have found human bones that clearly had been cut.

COLE: So there’s two potential explanations for why you might have a cut mark on a human body. The first is that yes, you are—you’re cutting it, you’re butchering that carcass to extract the flesh. Or the second explanation is that you are cleaning the carcass of flesh for some kind of ritual purpose.

TWILLEY: James says both kinds of cutting went on, if you look at the fossil record. Some cuts are the kind of cuts you’d make if you were stripping flesh from bone for burial—not for eating. And some cuts are the kind of cut you make if you’re butchering a body for food.

COLE: The key thing here is that the actual signatures, so the types of mark on the bone, are very distinctive. So if you’re butchering, you’re generally getting cut marks at points where you get things like cartilage. Whereas if you are cleaning the body for secondary burial, you get lots of scrape marks along the length of the bone. And what it looks like from the archaeological record is that most of the cut marks tend to fall around the locations where you would expect butchery marks to be.

GRABER: Bill agrees.

SCHUTT: So if you treat human bones the same way that you treat the game animals that lived in that area then that’s a strong indication that cannibalism took place.

GRABER: This was happening among all Homo species. Homo antecessor, Homo Neandertal, Homo erectus, for example.

COLE: And then our own species also seem to have engaged in this. So we have a sparse fossil record and within that sparse fossil record we are still picking up signatures of cut marks on hominin bones. So what that potentially means is that it probably was a frequent behavior because we’re picking up the signature of this act in a very small record to begin with.

GRABER: So we know it was happening. And we know it wasn’t super rare. But then why was it happening?

COLE: Okay, so when I was looking at the nutritional value of the human body, what I wanted to try and understand or establish was whether the act of cannibalism was actually nutritional in in nature.

TWILLEY: Obviously, James and his archaeologist colleagues mostly look at bones. And bones can tell stories, for sure. They can tell us that humans likely ate other humans. But they can’t necessarily tell us why those humans did what they did.

COLE: So what that means is that when these acts are looked at from the archaeological record, they’re generally boiled down to two very broad interpretations. On one hand it’s nutritional, or it’s ritual.

GRABER: Until recently, most archaeologists believed that cannibalism among our prehistoric ancestors was for nutritional reasons—they were hungry, there wasn’t much food, so other humans ended up seeming pretty tasty. And archaeologists thought that ritualized cannibalism—like for religious purposes or burial or war—that only started about 15,000 years ago among Homo sapiens.

COLE: And I wanted to know, okay, if we’re calling these acts nutritional, how nutritional are they compared to other animals that we knew were eaten by these hominins in the same time? So that’s why I wanted to look at the calorie values of a human being and then compare them to that of something like a mammoth or an auroch or other Ice Age fauna.

TWILLEY: This is really a very reasonable sort of thing to want to know. Are humans good food compared to a mammoth? But then when you start to think about it, how exactly do you go about figuring that out?

COLE: Yeah, so thankfully I didn’t actually do any sort of uh—I didn’t have to do any practical elements for the study.

GRABER: What James did manage to do was find four studies from the 1950s. The researchers had dissected four males. And the point of that research was to understand the chemical composition of the human body.

COLE: So what those studies did is that they broke down the values of the human body into protein and fat values amongst others. But what’s interesting for calories is that if you know your protein value and you know your fat value and you know the weights then you can actually convert those into calories. And fortunately in those 1950s studies, they had also recorded the weights of all the body parts that they were examining and they gave the protein and fat values of them.

GRABER: James just had to do some basic math.

TWILLEY: So break it down for me. If I ate one raw male, how long would I have to spend on the treadmill?

COLE: Okay, so kind of the average weight that came through from those four studies was 65.9 kgs and that returned a full body value—so that includes all of the organs and the guts and you know things that you would never even think about eating—but that returned kind of a value of about 143,770 calories.

GRABER: James has an amazing table that lists the calorie count organ-by-organ.

TWILLEY: Skin is surprisingly high in calories, folks. OK, so now James knows the caloric value of a human. A human male that is. No one has established the precise chemical composition of woman, so we don’t know how many calories we’d bring to the table. James suspects a little more thanks to our higher body fat percentage.

GRABER: Just another way women are underrepresented in science.

TWILLEY: James’s next step was to compare humans to the animals we know our prehistoric forebears ate.

COLE: A mammoth for example comes out almost, you know, three million, six hundred calories and a woolly rhino at one million, two hundred and sixty.

GRABER: James says that a horse would be about 200,000 calories, and a boar is about 324,000 calories. A lot more than a dude.

TWILLEY: Like really a lot.

COLE: And for me, you know, you get a much higher calorie return by going after a single horse or a single deer than you do by going after a single person or a group of people. And so that makes me think that maybe there’s something else going on here that’s not just about calories.

GRABER: Hunting is in fact hard work, but killing another human for food isn’t necessarily so easy either. We fight back. We have family members who might avenge our death. A human male is not a free lunch.

COLE: So I kind of concluded that it’s likely that there are social motivations behind these acts all the way back into antiquity, you know almost a million years ago. And it’s not just about survival cannibalism or the fact that you know you don’t have any other food to eat, although they’re almost certainly also happened.

TWILLEY: In other words, James says, you shouldn’t think of early humans as just these brutal desperate creatures. Even though the cut marks on some bones show that humans were eating each other as food, James is saying that at least some of the time, that wasn’t out of hunger. Instead, ancient humans were likely eating each other for much more sophisticated reasons, to do with spiritual beliefs about life and death.

COLE: So these are a culturally complex and culturally diverse species. Just in the same way that modern humans are culturally diverse and complex where we have different practices around death and burial throughout the world.

GRABER: That said, like James pointed out, our early ancestors and their hominid cousins were also probably eating each other when there was no other option around. And we know that still happens today.

SCHUTT: Well when you are in that type of a condition, where there’s no food and you are starving. You’ve eaten your pets, you’ve eaten the shoe leather, you’re eating hides. This is the Donner Party.

TWILLEY: The Donner Party is one of the most famous cases of survival cannibalism in recent history. It took place in the 1840s and it’s a gruesome, gruesome story, but the short version is a group of westward bound settlers left it too late to cross the mountains into California before the winter hit. So they got snowed in. Lots of them died. And the survivors ate them. One guy, Louis Keseberg—when he got rescued he had eaten nothing but humans for two months.

SCHUTT: When you get to that point then all bets are off. If you’re presented with the fact that there are dead around then you are either going to consume them and probably try to feed them to your children or your relatives or you’re going to die. And that is a choice that is made in those incredibly difficult circumstances, whether your city is besieged or whether there’s a horrible famine or you’re stuck in the Andes like the Uruguayan rugby players.

TWILLEY: Bill’s referring to the famous plane crash in 1972, where the survivors also ended up eating their fellow dead passengers, in order to survive.

GRABER: There are other famous examples of this happening on a much more massive scale. In Russia, during World War II, Leningrad was under siege for almost a full three years. Thousands of people ended up eating other people to outlast the siege. Lots of those survivors were later prosecuted for cannibalism.

TWILLEY: Or take the largest famine in recorded history, in China. It began in 1958, after Chairman Mao launched his disastrous Great Leap Forward—an agricultural modernization plan based on complete BS. The harvest failed repeatedly, 30 million people died of starvation, and cannibalism became widespread.

GRABER: This wasn’t the first time starvation cannibalism was documented in China. One researcher found 177 incidents of it, dating back more than 2,500 years. In the oldest example, families apparently started exchanging children so they wouldn’t have to consume their own relatives. Amazingly, the emperor actually made that practice legal in 205 BCE.

SCHUTT: The thing with China is, you know, it makes it sound like China is—that this always happens in China. Well, the thing is, that’s not necessarily the case but they took such amazing records. Their historical records are really unsurpassed. So they documented everything. So we now get to read about these examples of famines and the practices that they undertook in order to survive.

TWILLEY: But it wasn’t all survival cannibalism in China. After the break, we get into the peculiar practice of medical cannibalism. Which turns out of have been popular in the West, as well. In fact, it still goes on today.


TWILLEY: So here’s my question. If—as the archaeological evidence seems to show—cannibalism happened on a relatively regular basis among our prehistoric ancestors, when did it become such a horrifying taboo?

GRABER: Bill traces it back to the ancient Greeks. In the Odyssey, the evil giants eat people. The Greek gods became cannibalistic when they were upset. And then Bill says in Judaism and Christianity and in Islam, burial practices became super important and eating people was absolutely vilified. And, think about it: the body is basically the spirit made flesh in these religions. Jews can’t even be cremated because the body has to be intact for when the messiah comes.

TWILLEY: Christians eat the body of Christ and drink his blood as part of communion. If you’re Catholic, you are supposed to literally believe that the wafer is his body and the wine is his blood.

GRABER: This sounds like a pretty major contradiction, right? Eating a human body is absolutely taboo in Christianity. And yet for Catholics, transubstantiation is meant to be literal. But it just shows how powerful the idea is, that consuming his flesh and blood creates a kind of union with Jesus.

TWILLEY: In fact, it’s precisely because it’s so powerful that eating people just casually for a weeknight dinner—or even as part of a very solemn ritual that was outside the Christian church—that became one of the ultimate taboos.  And this anti-cannibal message gets spread not only through organized religion but also through popular literature.

GRABER: But if you’re not part of the Judeo-Christian tradition, you won’t necessarily share these world views.

SCHUTT: Culture is king. If you don’t get spoonfed through, you know, the ancient Greeks through the Romans and then the Shakespeare and the Brothers Grimm and Daniel Defoe that cannibalism is the worst thing that you can do to another person—if you don’t get that story, then you don’t have this knee jerk reaction that we all have now in the West about cannibalism and how horrible it is. In other cultures that did not get that as the party line, they developed their own rituals and medicines and practices and warfare and burial rites that sometimes involved cannibalism. And it wasn’t wrong to them, it was, you know, this was a ritual that they developed and and sometimes this is what they did to their loved ones or this is what they did in warfare. Or this is what they did when when they ran out of food or as a way to pay homage to their sick relatives.

GRABER: And this is exactly what happened in China. As we’ve said, the Chinese kept amazing records, so we have a better idea of what was going on there. It’s important to remember that these practices certainly weren’t limited to the Chinese.

TWILLEY: But there’s this Confucian concept in China to do with filial piety. Basically respect and care for your elders is really really important.

SCHUTT: In its extreme form, what would happen is that, if you had an elder or a relative who was very sick, that you would cut off a part of your own body, usually a part of your arm or a part of your thigh, and feed it to them as a sort of last resort medicinal treatment. And you know this was a fairly well accepted custom to the point where they had to make special laws so that people wouldn’t pluck out an eyeball or do something that extreme and feed it to grandma or grandpa.

GRABER: This is a form of what’s called medical cannibalism. And it’s not the only one in ancient China.

TWILLEY: Chinese scholars have documented the consumption of human organs and human flesh to cure diseases as far back as the Han dynasty, nearly 2000 years ago. Doctors would prescribe human bones and hair, but also toes and liver to their sick patients.

GRABER: But don’t let our Western taboo against cannibalism blind you here—Westerners also thought that consuming their fellow humans would help them get better.

TWILLEY: We called Shirley Lindenbaum about this, she’s a medical anthropologist. She’s Australian although she’s now based in New York.

SHIRLEY LINDENBAUM: That was also very old, as long ago as Pliny who thought drinking human blood was good for epilepsy. And then medicinal cannibalism was widely practiced, including not just blood but other body parts in Europe, from the sixteenth to the eighteenth century.

SCHUTT: This surprised me, given the taboo that we have in the West—that medicinal cannibalism was very, very common in Europe. Starting in the middle ages throughout the Renaissance right up until the beginning of the twentieth century, just about every body part you can think of was used for you know to treat any type of disease that you can think of. Kings were doing it, people who were rich were doing it, the poor were doing it. Everyone. For example, they would grind up bones. People would line up at at executions to collect blood.

GRABER: Like Pliny, they thought it’d help them cure epilepsy. Epileptics would literally carry a cup along to executions. And parts of the prisoners’ bodies were cut off for medical use, sometimes when they still alive. And this next one might be my favorite weird example of all.

SCHUTT: Mummies were ground up. So there was a real run on Egyptian mummies and it was all because of a mis-translation. There was an Arabian word called mumia, and that was this kind of tarry bitumen substance that they would use to bind wounds and they were also used in mummy preparation. But the Europeans mistranslated it. They thought mumia meant mummy. So they’d bring mummies back from Egypt and grind them up into a powder. It was actually sold on the Merck index into the 20th century, which to me was amazing.

TWILLEY: Western medical cannibalism fizzled out mostly after the Enlightenment and the dawn of modern medical science. But like Bill says, ground up mummies were sold into the twentieth century.

GRABER: And then there’s an example I had heard of but had never thought of as cannibalism that went on until only a few decades ago.

LINDENBAUM: There’s a kind of medicinal cannibalism in cadaver-derived drugs. Taking out pituitary glands, for example, for body building and for hormone growth in stunted children. That came to an end—that went on from about the 1960s to the 1980s.

TWILLEY: But there’s one last form of medical cannibalism that still goes on today. The final frontier.

SCHUTT: Yeah, I think placentophagy is probably the last remnant in the West of medicinal cannibalism. The belief is that by consuming your placenta after you give birth that you are in some way obtaining a medicinal benefit. Generally speaking the person believes that they are replenishing hormones that are lost, estrogen and progesterone that are no longer being produced by the placenta, which goes from a miracle organ to after birth quite quickly. And so there’s this belief that it levels out the ups and downs of postpartum depression.

GRABER: I frankly had never heard of anyone doing this—I think maybe I heard of some celebrities but I probably tuned it out.

TWILLEY: Oh my god, Cynthia, only Kim Kardashian West just ate her placenta for crying out gently. Where were you?

GRABER: I missed that. Nicky, though, you had a more personal connection.

SARAH RICH: Yes. I got a note from Nicky asking if I knew anybody who had consumed their own placenta. And I said I know someone very well. In fact, I have done that twice.

TWILLEY: This is my friend Sarah Rich. You might remember her as the proud owner of gold-plated flatware from our very first episode. She’s also a talented writer and editor, we have a link to her awesome new book Leave Me Alone with the Recipes on our website. It is gorgeous.

GRABER: When Sarah was giving birth to both of her children, like a bunch of her friends in the East Bay, she used a doula not only to help her with the delivery, but also to help her with her placenta.

RICH: She brings a cooler to the hospital, and when you give birth in Berkeley, which is where I did, I think maybe the hospital staff isn’t totally stunned when the request comes along to take the placenta in a cooler home. So that’s what she did. She took it like I think you would transport any organ in a cooler. And yes, she has a set up at her home where she dehydrates it and then grinds it up and encapsulates it. And she brought it to me in a little glass jar a few days later when she came to check on me. And so yeah, I took a capsule once or twice a day.

TWILLEY: As Bill said, one of the things that motivates new mothers to eat their placenta is a belief that it will help ward off any postpartum depression. And that’s what motivated Sarah too.

RICH: I think for me the primary one was a curiosity to see whether it would have a positive effect and a fairly certain notion that it would probably not have a negative effect and that if anything it might have a placebo effect, which was fine with me.

GRABER: In fact, Bill thinks the placebo effect is probably what’s going on. But he says very, very little good research has been done on this practice.

SCHUTT: As a matter of fact some of the research that’s been done indicates that if anything at all it may have an analgesic effect. It may act as something that enhances the body’s own opioids. But if you’re not eating it till two weeks after your baby is born then there’s really no effect there. But if you’re looking at this thing as a way to replenish hormones, as soon as you cook it, you’re denaturing those hormones.

TWILLEY: Now cooking may not be rendering them completely inactive—some research shows that it’s possible to be exposed to hormones in meat after cooking.  It’s also possible that drying and grinding would have a less destructive effect.

GRABER: There really hasn’t been any good research on this, and, as of yet, none showing that eating your placenta affects hormone levels after birth.

TWILLEY: But you know what, the placebo effect is one of the strongest drugs out there. And, either way, eating her placenta seems to have worked for Sarah.

RICH: Well, I don’t think I experienced postpartum depression, and so, in as far as I could say it helped me avoid postpartum depression….maybe it did? I don’t know.

GRABER: A lot of doulas say that eating your placenta is a quote natural thing to do. And yes, some non-human animals do eat their placentas after giving birth.

SCHUTT: There are various hypotheses for why that might be so. For example, if you give birth and then you get rid of the after birth, it’s not going to attract predators. And it’s also a nutritional boost. You’ve just gone through this stressful period. The last thing you want to do is go out hunting and there’s this big slab of meat. And so it sort of makes sense in the animal kingdom. But it doesn’t make a whole lot of sense in humans. And so it’s not surprising that you don’t really see a lot of it.

TWILLEY: Although Shirley has seen evidence of it in her anthropological work with remote tribes. But it’s not common.

GRABER: Bill says this practice really became slightly more popular among humans only in recent decades.

SCHUTT: And so what started out as sort of a rarely performed sort of hippie thing back in the 60s, relatively recently has turned into something a bit more as a facet of alternative medicine

TWILLEY: A lot of placenta eaters take the pill route, like Sarah did. And pills are relatively tame, honestly although Sarah said hers didn’t smell great. But some women choose to eat the placenta as a meat. Bill was curious, so he called a doula named Claire to find out more

SCHUTT: I gave her a call. And we got along really well, I figured OK, well, maybe we’ll Skype or Facetime or phone interview. And she said, well that’s too bad because I just gave birth to another child and if you came down here you could eat my placenta. My husband’s a chef. We could prepare it any way you want it. We could make, you know, we could make a taco out of it or you can have it osso bucco. And I’m going, what? I’m thinking to myself, you just invited me down to Texas to eat your placenta!

GRABER: I have to admit that at this point in the interview I was having a bit of a tough time listening. I honestly did not want to hear about Bill eating this woman’s placenta for dinner with her family. But he did, and he told us about it.

SCHUTT: He prepared it osso buco-style and I cleaned my plate. I would never do it again but it was certainly something that I’m glad I did.

TWILLEY: So of course I wanted to know, what did it taste like?

SCHUTT: It had the consistency of veal and it tasted—this is not the most popular food but what I thought of immediately was back when I was a college student, we used to get together on Sundays and everybody would  watch football and we’d throw a bunch of real garbage-y food together. And people would cook up chicken gizzards. And it reminded me of a chicken gizzard, the taste. Sort of an irony, organ meat-taste. It was kind of tender. It reminded me of veal that tasted like a chicken gizzard. That’s about as close as I can get to a description.

TWILLEY: So now you know. But you might be thinking, how is this cannibalism? Sarah certainly didn’t think of it that way.

RICH: It felt to me like eating a part of my own body. And I didn’t really frame that in my head as cannibalism.

GRABER: But in Bill’s definition of cannibalism, eating parts of your own body counts.

TWILLEY: What’s more, the placenta is part fetus. So that’s more like the parents-eating-the-kids version of cannibalism. Part of the kids anyway. Sorry Sarah.

GRABER: So placenta eating, and Chinese filial piety, the Europeans and mummies—these are all forms of medical cannibalism. Another common form of cannibalism, common at least where cannibalism is practiced, is ritual. Like James said, rituals around warfare and religion and burial.

TWILLEY: And that brings us back to Shirley Lindenbaum, the Australian medical anthropologist.

LINDENBAUM: So in 1957, a colonial government physician called Vincent Vegas noticed this new disease.

TWILLEY: And the disease is killing lots of indigenous Papua New Guineans called the Fore people.

SCHUTT: Once the press got a hold of it they started to call it the laughing death or the laughing sickness. And no one knew what it was from. Some people thought that it was from stress-related contact with Westerners. Other people thought it was toxins that they were getting into their system somehow.

GRABER: Another theory was that this laughing sickness—”laughing” because people basically just lost their minds—that it was a genetic disease. This is where Shirley comes into the story.

LINDENBAUM: So in 1961, the Department of Genetics asked me and my husband then, John— uh, Bob—to go to Papua New Guinea and collect data about Fore social life. And in particular they wanted kinship studies because they were interested in the genetics of the disease. I was in my 20s.

TWILLEY: So Shirley and Bob—yes, they have since divorced—they traveled around Papua New Guinea. And they quickly realized that the genetic theory just didn’t hold up. Because the people who were getting sick were not related in the biological sense. The Department of Genetics had got confused because the Fore had these elaborate non-biological kin structures.

GRABER: The people Shirley spoke to remembered some of the earliest cases of this disease, which by now was called kuru. They even remembered the names of the people in their communities who first died from kuru.

LINDENBAUM: So we said, what happened to them? And they said, well, we ate them. So we said, you ate them? We knew they were cannibals but we didn’t know that they’d eaten the kuru victims. So we thought, well, we had better change our study a little bit here.

TWILLEY: Shirley eventually learned that when a Fore woman died, the tradition was that her husband’s family had to hold a massive feast for her funeral. And as part of that feast, they would eat the dead person. The entire dead person. Including the brain, which was mixed with ferns and then cooked.

GRABER: There are a couple of reasons the Fore performed these funeral rites for their dead. One was to get rid of the dead person’s spirit.

LINDENBAUM: So the Fore thought that there was the spirit of the dead person still hovering over the body and if that person had been maltreated or had a grudge against any of the people it would bring problems to the husband’s lineage.

TWILLEY: Eating the person meant the spirit couldn’t do any harm. The women even thought it might make them more fertile. And the other reason was—well, the belief was that the dead woman had given children from her body to her husband’s family. She had enriched her husband’s lineage with new bodies. So her original family—the idea was that they should be paid back for that gift by at least having the chance to eat her body now that her husband’s family wasn’t using it anymore.

GRABER: Shirley figured out that the disease was caused by cannibalism because only women and children were getting the disease. And only women and children ate the dead bodies.

LINDENBAUM: We went to the Kuru conference in Adelaide, told everybody what we thought. Nobody believed us.

TWILLEY: But eventually medical science proved Shirley right. For one thing…

LINDENBAUM: We now see that nobody born since 1960 has ever come down with the disease. And 1960 was the time when the missionaries and the government officers went through on patrols and said, “You’ve all got to stop fighting, men and women should live in houses together, and you’ve got to give up cannibalism.”

GRABER: The reason this whole story is important is that this is how we learned about prion diseases, which are caused by eating brains of your own same species. There was a Nobel prize for this discovery. Turns out, kuru is basically the same disease as mad cow disease, which you might have heard of, which cows got from eating other cows’ brains in their feed.

TWILLEY: And which is the reason I can’t give blood in America, because I grew up in England eating these potentially contaminated hamburgers. What’s a little scary is no one knows how long mad cow disease takes to develop. So watch this space.

GRABER: Like Bill said at the beginning of the show, cannibalism definitely has some pretty serious risks associated with it.

TWILLEY: But for the Fore it was important. It was the right way to treat the dead.

SCHUTT: You know, there were examples of this happening back in the 1960s and 70s, anthropologists would go into South America, for example, and they would come across a group that had little contact with Westerners. And these people were just as freaked out to learn that that Europeans were burying their dead as the anthropologists were to learn that these people were eating theirs.

GRABER: Cannibalism is, as we said, a serious taboo in the west. And so when Westerners come across people who do practice cannibalism, those people are often labeled primitives or savages.

TWILLEY: In fact, this is the likely origin of the term cannibal exactly this sort of prejudice. The word cannibal only came into use in 1553. Before that, humans who ate humans were called anthropophagi.

SCHUTT: There are a couple of different possible origins for cannibal. And that it is a corruption of one of the indigenous groups of the Caribbean who were called the Caribs. There are certain researchers who believe that Canib is a sort of a distorted way of pronouncing Carib.

GRABER: There are other theories, but this one seems to be the most likely—that it’s what the Spaniards called the inhabitants of islands in the Caribbean.

SCHUTT: This was one of the most horrifying aspects of the book. When Columbus came over—he made four trips to the New World, and on his first trip, the people that he ran into in the Caribbean were described as kind, many of them, and they were fit to become good Christians. And he reported this back to Queen Isabella. And you’ve got to realize that what he was looking for was gold and when he didn’t find gold then in a sense the next best resource became humans—slaves. And so the third and fourth trips back to the New World were, in a sense, they were armed invasions. And all of these groups that had previously been described as you know kind and nice people, we got along with them, they were beautiful—all of a sudden, they were cannibals. And Queen Isabella had said to him, listen, you’ve got to treat these people well but if they’re cannibals then all bets are off. And lo and behold on the third and fourth trip: What a coincidence! No gold but plenty of cannibals.

TWILLEY: And if they were cannibals—well, Columbus had been told exactly how to treat them.

SCHUTT: And so that justified stealing your land, stealing your property, raping, killing, hunting you like you were a dog. And it’s because they were able to to justify this by saying well, these weren’t humans, they were cannibals.

GRABER: There’s debate about whether the native Caribbeans were even eating other people. Some say no. Others say it was a funerary practice, just like with the Fore.

TWILLEY: Either way, that didn’t stop colonial powers from using it to exploit and subjugate thousands of native people.

GRABER: But even if the locals were practicing funeral cannibalism, they certainly aren’t today. Almost no one is. Anywhere.

SCHUTT: I think because of the influence of Western culture that if it does take place that it’s done in private and it’s probably done a lot less often then than it ever was before. And I believe that this is because of the major influence that the West has had on many cultures. So if you found a culture someplace that was untouched by Western civilization—and how many of those are there?—then you probably, you may find people who haven’t heard from the guys who hand the T-shirts out that cannibalism is the worst thing you can do, that you need to stop doing that.

GRABER: Which—and I’m the squeamish one here—is not necessarily a sign of world improvement. Remember, some communities thought we were barbarians for putting our dead in the ground and burying them. It’s just a different mindset.

TWILLEY: But perhaps because actual cannibalism is rare today, the few cases we do see are the crazy gory sensational ones. You get the serial killers, you get Ed Gein—he’s the one Hannibal Lecter was based on. You get Jeffrey Dahmer, you get that German guy who advertised for a person to eat online. And then ate him.

SCHUTT: There’s a spectrum of criminality and mental illness that that winds up on occasion manifesting itself in murder and cannibalism.

TWILLEY: We are horrified by these people and yet, judging from the movies and the news coverage and the books, we are also kind of fascinated.

GRABER: Another thing we love? Zombies. Who also eat people. There’s the Walking Dead and the Santa Clarita Diet, and my personal favorite, the murder-solving brain eater in iZombie.

(iZombie theme music)

TWILLEY: See, Cynthia. You act all squeamish but you love cannibalism really.

GRABER: I close my eyes every time she eats brains. But she is really funny.

TWILLEY: We asked Bill why he thinks cannibalism has such a hold on our imaginations these days. He wasn’t sure, but he had a theory.

SCHUTT: When I think about that, I think of, take the number one Western taboo arguably and now add food. Right? And so you’ve got something that is fascinating.

TWILLEY: This episode was suggested by one of my favorite listeners, my husband Geoff. And to Geoff, the fascination with cannibalism is not just that you’re mixing a taboo with one of the most fundamental substances to our survival: food.

GEOFF MANAUGH: It’s that you are food.

TWILLEY: Geoff has been giving me cannibal books as a not-so-subtle hint for at least a year now. Seriously, I have quite the cannibal library. So I asked him why he wanted Gastropod to make a cannibalism episode.

MANAUGH: I think what’s interesting to me about cannibalism and its relationship to food is that we become the thing being hunted or we become the prey. And it’s such a powerful motif in horror, from movies like “Jaws” where human beings become food for animals or even “Jurassic Park” where we’re being hunted by these resurrected dinosaurs. When you have the figure of the cannibal, it’s this other human life form that wants to eat us, we become food and lose all of our power and I think that’s the origin of the horror of cannibalism.

GRABER: Happy Halloween!


TWILLEY: Thank you, Geoff!

GRABER: Yeah, thanks Geoff. Thanks to Bill Schutt, author of Cannibalism: A Perfectly Natural History.

TWILLEY: Thanks also to James Cole and Shirley Lindenbaum, we have links to their papers, books, and research online. And a particular thanks to my friend Sarah, we have a link to her new book on our website at gastropod.com. It’s gorgeous and you should check it out!

GRABER: And thanks as always to our amazing volunteer, Ari Lebowitz. We promise that in two weeks we’ll be back with something much more appetizing.

TWILLEY: Meanwhile, we’ll let James have the last word this week.

GRABER: And is your calorie count for this average man raw or cooked.

COLE: Raw. The calorie values would change when cooked, but I really didn’t have any way—or much desire I have to admit to try and explore that option.