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.

PRE-ROLL

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.

MID ROLL

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—.

WOLFE: A B+—.

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.

MID-ROLL

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.

TWILLEY: And?

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.

MILLER: Yep.

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.