This is a transcript of the Gastropod episode Dishwashing Debates: The Soapy Science Behind Everyone’s Favorite Chore, first released on November 19, 2024. It is provided as a courtesy and may contain errors.

DAN SOUZA: What’s funny when I was thinking about talking about this today is so much of this stuff is like at the heart of a lot of arguments within relationships. I feel like, I think there are marriages that are strengthened or hurt by what happens in and around washing dishes.

NICOLA TWILLEY: To be honest, there are few things that are *more* contentious than the correct method of washing the dishes. Unless perhaps it’s the correct way to load a dishwasher, which is deeply divisive.

CYNTHIA GRABER: We at Gastropod are here to solve these debates once and for all, and to tell you—and whoever you are sparring with—which one of you is right.

TWILLEY: It’s you! Or, really, me. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber, and this is Gastropod, the podcast that looks at food through the lens of science and history. This week we’re not looking at food, but rather what happens to its aftermath: the clean-up.

TWILLEY: Assuming you don’t have servants, which sadly neither of us do, post-meal clean up is a task that has to happen on an extremely regular basis. And even though we never think about it, all the tools we use for that clean up had to be invented. So we wanted to know about this history: how did people wash dishes before dishwashers and detergent?

GRABER: And we wanted to know, if you have a dishwasher at home, is it better to use that, or should you be doing the dishes by hand? And what’s with all the dishwashing pods you can find in the stores these days—are they really better, or just more expensive? Or could they actually be a worse choice?

TWILLEY: These are the questions of our time and this is the episode with the best answers science and history can offer. It’s supported in part by the Alfred P. Sloan Foundation for the Public Understanding of Science, Technology, and Economics. Gastropod is part of the Vox Media Podcast Network, in partnership with Eater.

[MUSIC]

GRABER: So how did people wash dishes in the past, before all the necessary ingredients like electricity and indoor plumbing and detergent and dishwashers?

TWILLEY: Short answer, we don’t really know.

GRABER: There are historical recipe books and books about household management, but there’s very little on washing the dishes.

TWILLEY: Cooking, doing laundry, all of it gets more airtime than washing dishes. But in part that’s because for most people, for most of history there weren’t all that many dishes to wash.

GRABER: Most meals were eaten right out of the pot they were cooked in. From what we know, for most people in medieval Europe, a flat round of bread was usually the plate—it was called a trencher. If you did happen to have a plate plate, it was typically wooden, and you didn’t wash it, you just wiped it clean.

TWILLEY: And people didn’t have a ton of cutlery either, often just a single personal knife or spoon. Forks were late to the party, as you’ll know if you’ve listened to Gastropod’s very first episode.

GRABER: But people did clean things, and they occasionally even cleaned things that they used for cooking and eating. There’s a little ceramic figure from China of someone scrubbing a pot in a tub from about 1500 years ago. This was how you cleaned up after the meal in the past: you filled a tub with heated water and scrubbed away.

TWILLEY: Sadly, there’s not enough detail in that Chinese ceramic to show exactly what they’re using to do the cleaning, but we do know that soap was invented thousands of years ago.

GRABER: For most of history, soap has been made by cooking two things together: it’s a combination of a fat, either animal fat or a vegetable fat like olive oil, heated up together with an alkali. Alkali just refers to a substance’s chemical properties—it’s the opposite of an acid. A popular alkali was wood ash from a fire, or in ancient Rome, apparently cuttlefish bones were also super useful in soap-making.

TWILLEY: The two ingredients—fat and the alkali—when they’re combined, some very cool chemistry happens. It’s literally called saponification, or soap-making. The final product, soap, does a couple of things. It helps water to not stick to things so the water can flush dirt away more easily, and it encapsulates dirt, too. Both of these properties make soap soapy, for cleaning.

GRABER: That soap came in bar form, it was a solid. Women traditionally made that soap at home, or if they lived in cities they could find soap in the shops by the mid 1800s, but they had to shave it up to make sudsy water, because it’s just hard to to get the water to be soapy enough by rubbing a bar through it.

TWILLEY: A big breakthrough in the dishwashing universe was something called the soap saver.

SUSAN STRASSER: It’s sort of like a little cage, on a stick? And the cage opens and you can put slivers of soap. So, if you had bar soap and you had a little soap left over, you would put the sliver of soap in that little cage and then swish it around in the dishwater to make soapy water.

GRABER: Susan Strasser is an emerita history professor at the University of Delaware and she’s the author of a book about housework called Never Done. She says that people also used metal scrubbers, these were available from about the mid-1800s onwards, or they might have used rags—basically whatever they could find.

STRASSER: Sand was a big thing, um, to use to scrub.

TWILLEY: In magazines and housekeeping manuals from the time, Susan has found tips on scrubbing with salt, soda, borax powder, clay, and all sorts of other things.

GRABER: But the actual biggest issue before plumbing wasn’t the soap or what you used to scour the pots and dishes, it was the water.

STRASSER: And the most important thing to remember about water is that a pint’s a pound the world around. That, it’s heavy. It’s really heavy. It’s hard to haul a lot of water. And so the important thing about dishwashing was, conserve water as much as you can.

TWILLEY: Before the glories of indoor plumbing, women—and it was usually a woman’s job—they had to go fetch water and haul it back to their kitchen by hand. The water might be coming from a few blocks away at a city pump, or fifty or sixty yards away, from a well, or even further, from a river or lake. And they had to slog back home with all that water,

STRASSER: I have a dehumidifier in my basement and I have to lift the water from the floor of the basement to the utility sink. It’s heavy! It’s heavy. And you know, I try to lift weights from time to time. I try to keep myself strong. But to think about how much water women were hauling all the time.

GRABER: It was a lot of work to get all that water home, so people were pretty miserly with it. When it came to dishwashing, they filled two tubs. One had cool water in it, that was for the rinsing, and one had to be lifted onto a stove and heated up for the cleaning.

STRASSER: And then when you think about so much of it being hot water, it becomes not only grueling work, difficult work, but also potentially dangerous. I mean, you could scald yourself.

GRABER: And so you can imagine that it was a huge transformation for a household, and particularly for women, when homes started to get indoor plumbing. That didn’t happen until really pretty recently.

STRASSER: Well, I would say it started to change in about the 1880s. But how much it changed for whom was really a matter of class. Not only of class, but also of urban and rural differences. So, really, for working class people in urban areas? I don’t think that it really started to change until the 1920s. That you really had large numbers of people who had running water in their living spaces.

TWILLEY: The impact of indoor plumbing was a huge, huge saving of women’s time and effort. You can hardly imagine how much time women spent hauling water in the past, unless you look at parts of the world today where women and girls still have to do exactly that. UNICEF says in places without plumbing, women and girls spend on average more than two hours collecting water every single day!

GRABER: In America once people had indoor plumbing, they were no longer quite as worried about conserving water. Susan says that in Philadelphia, water consumption per person doubled in the first 14 years after the city built its public waterworks. Of course this wasn’t just from dishwashing, people also were less miserly with washing laundry and with bathing, but it all added up. And everything was cleaner.

TWILLEY: Indoor plumbing for the win. But, women of the 1800s, have I got something super exciting for you! How about a machine to wash those dishes?

GRABER: Because at about the same time as indoor plumbing started to come into existence, early to mid-1800s, inventors started to turn their minds to how to use that flowing water to clean dishes mechanically and save even more labor. A guy named Joseph Houghton patented the first dishwasher design in 1850.

ALLEN CLAUSS: Now, it was a really crude thing. It was a wooden box with a crank on it that pumped the water around in there and splashed it over the dishes. That never really got commercialized.

TWILLEY: Allen Clauss is a chemist who spent a large chunk of his career in R&D at Proctor and Gamble, which makes a lot of the world’s dishwashing detergent.

GRABER: Houghton’s design was basically like an open tub with dishes and water splashing around—it really didn’t work very well. But those early designs were the spark that inspired the woman who is usually credited with, quote unquote. “inventing the dishwasher.” She was a wealthy socialite from Illinois named Josephine Cochran. She of course had servants, and they did the dishes, but she was really unhappy with their dishwashing skills.

LOTTA KINITZ: When the servants were cleaning them, sometimes something broke. And sometimes things got chipped. So they got a little bit broke, and she was very dissatisfied with that.

TWILLEY: To be fair, Josephine’s dishes were family heirlooms from the 1600s, so it wasn’t unreasonable to be a little annoyed. And the woman telling us this story is Lotta Kinitz, she’s a test editor at a German magazine, and she wrote her PhD thesis on dishwashing.

KINITZ: And so she first wanted to do it herself, because she said they can’t do it. I can do it better. Let me do it. But then she realized how much work it was, especially if you threw a big party, to clean everything up yourself. And so she came from a family of engineers and, yeah, got into thinking, how could this be made easier? How could it be automated?

GRABER: She had the idea—and this was different from the earliest dishwashers—she thought you could put dishes on wire racks inside a copper boiler, and then spray all those dishes with hot soapy water. She tested this idea in her home sink, and then she hired an engineer to actually build it.

KINITZ: And yes, she kind of made a prototype and developed the first dishwasher.

TWILLEY: Josephine’s first dishwasher was still hand-cranked. But the idea of spraying the dishes—that was her innovation, and it’s still pretty much how dishwashers work today. She got her first patent in 1886 and promptly hit the road to start selling her magical new device.

GRABER: Josephine thought that wealthy housewives like her would be interested, but they weren’t biting. The machine was quite expensive, it was like two and a half to three thousand dollars in today’s money. Servants were cheaper.

TWILLEY: So Josephine pivoted. She went to Chicago, and she sold two of her machines to hotels. Hotels washed a lot more dishes, and they were convinced that her machines would pay for themselves by saving on labor and broken dishes, as well as giving them a more hygienic wash.

GRABER: Josephine made a particularly big splash at the Chicago World’s Fair in 1893. Nine of her machines were used there, they were a huge success, and she won a major prize at the fair. It was one of the very few inventions by women to do so.

TWILLEY: Josephine died in 1913, she never saw her invention become ubiquitous. But her company was bought by KitchenAid and then by Whirlpool, so her legacy really does live on.

CLAUSS: But it was still a very long time until it caught on and became common in US households, well after the clothes washing machine, which was actually invented later.

STRASSER: It didn’t really become commonplace until the 1970s. I grew up in a household without a dishwasher. Or, as my father used to say, I have four dishwashers—meaning the four children.

GRABER: Child labor is always going to be the least expensive option, but one reason that dishwashers weren’t quite as useful in the beginning as they theoretically should have been was because nobody had invented dishwashing detergent. That story’s coming up after the break.

[BREAK]

TWILLEY: So we said that soap goes way back, and that is of course what people historically used to do their dishes. But these days we use detergent. So how did soap become detergent—and what’s the difference anyway?

GRABER: Until really quite recently in human history, all soap was natural soap. Like we said, it was made from animal or vegetable fat with an alkali. This was great for washing hands and bodies, but when it came to doing the dishes, there were some limitations.

TWILLEY: Natural soaps are not great at cutting through the kind of heavy grease that can be left on dishes and pots. And they often react with water in a way that isn’t fantastic either.

CLAUSS: When you try to wash dishes in hard water with soaps, you tend to have a problem with soap scum leaving films. Particularly on glasses, you know, where you can really see it, but even on ceramic dishes, they’re not very shiny and don’t look perfectly clean.

TWILLEY: Hard water just means water with a lot of minerals in it, usually calcium and magnesium picked up from the rocks the water has percolated through. Soap molecules react with that calcium and magnesium and produce a scum.

GRABER: Luckily scientists found a solution, pretty much by accident. In Germany in World War I they were short on animal fat, and so researchers started trying to make soap from coal tar instead. It took a while to get it to work, but by the 30s, they’d nailed it.

TWILLEY: The result was synthetic detergent. It cleaned things the same way soap does but because it’s chemically different, when it reacted with hard water, it didn’t form a solid scum.

GRABER: The first synthetic detergents were for laundry, not for dishes. Proctor and Gamble sold a product called Dreft in 1933. And even though it was meant for laundry, they also had ads showing housewives sprinkling it into tubs to wash dishes.

AD VOICEOVER: She uses Dreft, remarkable new suds improvement. And here’s what happens when these dishes have been rinsed and allowed to dry by themselves. See? No trace of scummy dish pan film. They’re sparkling clear, without polishing!

TWILLEY: The next breakthrough in detergent also came about kind of by accident. Scientists were working on another problem with hard water. Even when you don’t add soap, if you evaporate hard water, the minerals precipitate out and form limescale. That grody white gunge was really an issue in the era of steam engines, because it would clog up valves and pipes and lead to explosions. Which is why, in the 1920s, researchers at the US Bureau of Mines began to tackle the problem of limescale.

GRABER: They came up with a nifty solution: just add something called phosphate. We talked a lot about phosphate in our episode on fertilizer. Phosphate is a naturally occurring mineral, it’s a combination of the elements phosphorus and oxygen, and phosphorus in fertilizer is an essential food for plants. But it turns out that phosphate is also an awesome water softener. The phosphate surrounds the minerals so they can’t stick to your pipes.

TWILLEY: And so in the 1930s, one of those researchers at the Bureau of Mines patented a new product called Calgon—short for calcium gone—that was filled with phosphates. It was marketed first of all as a water softener. It was used everywhere in industry, anything that relied on hot water—from mining to dairies. But before long Calgon also started advertising itself as something you should add to your home laundry washing machine, to stop it from gunking up too.

GRABER: And once people did that, they were surprised to find out that not only did phosphates prevent limescale, but they also actually improved existing detergents. Because that early Dreft powder, it was great, but it still wasn’t perfect, in part because it did still react with the minerals, and clothing didn’t get perfectly clean.

TWILLEY: Whereas when you combined detergent with phosphates, you didn’t get that reaction, but also, you got a whole load of unexpected added benefits. Phosphates turn out to help with cleaning: they break up grease and oil, they improve a detergent’s ability to grab onto dirt, and they help keep dirt suspended in water so it doesn’t settle back on the surface you’re trying to clean.

CLAUSS: The combination of synthetic detergents and phosphates was truly a breakthrough in cleaning your laundry.

GRABER: As Allen says, once again, these phosphates were first introduced in laundry products, most notably Tide in 1946. Tide was a huge success, and it sold out faster than P&G could make it. And that’s because people were using it for everything—including hand-washing dishes.

TWILLEY: But here’s the thing: phosphates are really hard on your hands. People used gloves to avoid what they called dishpan hands, but it is really gnarly to soak your hands in Tide-water.

GRABER: So soap companies took these new synthetic detergents and they mixed a bunch of them together *without* phosphates in a way that would foam up and clean really well but also not leave your hands rough and red.

CLAUSS: The, the big companies making and marketing hand dishwashing detergents really homed in on the message that it was gentle on your hands. And there were commercials that had the women even soaking their, their hands in the dish detergent. And saying, oh, you know, my skin still feels good and so forth.

WOMAN: Yes, for sparkling dishes, for soft, smooth hands, there’s nothing like wonderful Ivory Snow.

MADGE THE MANICURIST: Softens your hands while you do the dishes.

CLIENT: Pretty green.

MADGE: You’re soaking in it.

CLIENT: The dishwashing liquid?

MADGE: Palmolive!

CLIENT: Mild, then?

MADGE: Oh, more than just mild.

CLAUSS: They were much better than using soap to clean your dishes, natural soap, and they caught on pretty quickly for washing dishes at the sink. And there were a number of brand names, joy and ivory.

VOICEOVER: Dishes go from grease to shine in half the time, with Joy!

SINGERS: Yes! Joy in a bottle — beats anything in a box!

TWILLEY: These new dishwashing detergents were also liquids, not powders or flakes. And they were all the rage in the 1950s. Companies advertised them heavily to their target audience, the lady homemakers, by sponsoring dramatic serialized TV shows—yes, the kind of shows we call soap operas.

GRABER: As it happens, this is literally because the shows were sponsored by soap-making companies. In the 1930s, these serialized dramas started on the radio and aired during the daytime, and the radio networks wanted to get sponsors that would match their target audience: these lady homemakers who were cleaning a lot. And so they enlisted the support of all the big soap companies. Hence, soap operas.

[ORGAN MUSIC]

NARRATOR: The Brighter Day, brought to you by Drift. America’s favorite brand for dishes.

TWILLEY: As the soap companies experimented with all the different molecules they could make from petrochemicals, they came up with better and better synthetic detergents that behaved exactly how consumers wanted them. And they’d formulate their products to target different particular consumer desires.

CLAUSS: Gentleness to hand was a segment, okay? Cleaning better was a segment, particularly grease. And there was one product that came out much later than the earliest ones called Dawn that was particularly effective at cleaning grease. So effective it was used for crazy things like cleaning crude oil off of waterfowl, [LAUGH] you know, and things like this.

GRABER: Remember the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 that covered all sorts of animals in oil? And how that oil could literally kill them?

REPORTER: There’s a lot more to washing pelicans than there is to washing dishes, but they do have one thing in common. Remember Madge, the manicurist?

ADVERTISEMENT: You’re soaking in it. The dishwashing liquid? Palmolive!

REPORTER: Yeah, well, what the pelicans are soaking in is Dawn. Animal rescue folks have been using it for 30 years.

CLAUSS: Now that’s a bit tougher on your hands than ivory liquid, for example. So depending on what the, the user wanted, the products were formulated a bit differently and differentiated somewhat along those lines.

TWILLEY: Back in the 1950s when these new liquid detergents were taking off, it was the era of better living through chemistry and Americans loved their sudsy, petro-chemical based dish soap for hand washing dishes.

GRABER: And in the 50s there was finally also phosphate-enriched detergent for dishwashing machines. The problem before had been that detergent like Tide was just too sudsy.

SOUZA: I think probably most of us—hopefully just one time in our lives, one time or less, have used the, the dish soap instead of the detergent in the dishwasher. And that’s where you see like: Oh, wow, foaming is a really big deal, and your, your kitchen looks like a foam party, you know, in Cabo or something like that.

GRABER: Dan Souza is chief content officer at America’s Test Kitchen, where they study the best recipes, tools, and techniques for everything in the kitchen, including dishwashing.

TWILLEY: Fortunately the chemists persisted and by the 50s, they’d come up with low-foam detergents and foam suppressants, and Cascade and Finish were launched! Finally, dishwashing machines had their own detergent and could clean effectively.

GRABER: But it wasn’t all good news: another big change was happening at around the same time. Scientists started to notice that all this phosphate that was being used for things like laundry detergents, it was also causing problems in lakes and rivers. As we said, phosphorus is a source of food for plants, and that includes algae. All that phosphorus in the water led to algal blooms that were overwhelming water bodies and killing off other life.

TWILLEY: Detergent wasn’t the only source of phosphorus in our water—we first talked about this problem back in our fertilizer episode and fertilizer was a significantly bigger source. But manufacturers were eventually forced to take phosphorus out of their detergent: first laundry detergent, and then, quite recently, dishwashing detergent.

GRABER: And consumers really noticed the difference.

MAN: We’re seeing in our glasses a film and splotchiness.

WOMAN: They look cloudy and… it’s hard to explain. Like they’re smudged, like they’re… like they’re dirty.

REPORTER: No, it’s not your dishwasher or just your house. It’s a nationwide problem. The reason? The elimination of phosphates in dishwasher detergent.

CLAUSS: And that left a big gap in the cleaning ability of both laundry detergents and automatic dish cleaning detergents.

TWILLEY: But luckily for all those angry customers with their scummy dishes, Big Detergent had yet another cleaning solution that they were working on behind the scenes. Enzymes.

CLAUSS: Okay, well, enzymes out in nature are effectively used by both plants and animals to break down, digest and dissolve different materials.

GRABER: We make enzymes in our bodies to do all kinds of things, some of our homemade enzymes break down fats and starches and proteins—

CLAUSS: You know, some enzymes can break wood down. So when you see wood rotting in the forest, it’s enzymes that are doing that, okay. That are released from fungus and yeast and bacteria. So, you know, the people that were formulating detergents got on to this and said, wow, you know, if enzymes can break down all these things out in nature, why don’t we have them break down soils, that are on our clothes and on our dishes?

GRABER: This is a different way of cleaning from all the other ingredients in detergent. Some ingredients in detergent loosen and lift up soil, others do things like making water less sticky so it carries that soil away.

CLAUSS: Enzymes chew things up. Okay. The—enzymes break down the basic chemical bonds so that things like protein are broken down into amino acids. Starches are broken down into simple sugars. And then these simple building blocks are soluble and they wash away. So a big old protein that’s, you know, that’s sitting on your—on your plate when you’re trying to clean it. If the enzyme can break that down into a bunch of little fragments. They just come off and they just dissolve off into the water.

TWILLEY: Research into using enzymes in detergent goes way back. Already in the early nineteen teens, a German company was trying to commercialize a pre-wash soak with an enzyme from a pig pancreas in it. But at the time, we didn’t know how to make enzymes ourselves, and pig pancreases were in high demand to make insulin, so that product went nowhere.

GRABER: Then, in the 1940s, we got better at making enzymes, using bacteria to do the job. But the other problem was that they’re pretty sensitive, they break down really easily and so they weren’t super useful for a commercial product.

TWILLEY: The first stable one hit the market in the early 1960s, it used the same enzyme German researchers had identified in the nineteen-teens, but it was manufactured using microbes rather than extracted from a pig pancreas. A Dutch company and a Swiss company came out with enzyme-enriched detergents, but they were marketed as specialist products for washing blood-stained laundry from hospitals or slaughterhouses.

GRABER: But research continued, and then in the 1980s and 1990s, the number of different enzymes available to use in detergents for both laundry and for dishes started to really grow.

CLAUSS: Enzymes is enormous. I mean, it started off with one or two kinds of enzymes and now there’s a half dozen kinds of enzymes that are commonly used in detergent formulations. And they really work. And they can be targeted because of the different types of enzymes that are out there in nature. And, you can go after carbohydrates, you know, sugar and starch-based soils with certain kinds of enzymes. Protein-based soils with other types. Fat based soils with other types. So there’s a cocktail of enzymes in many of the detergents today.

TWILLEY: As phosphates were phased out, these enzymes became more and more important—first for laundry and then for dishes.

CLAUSS: Nobody’s ever figured out how to totally replace phosphates, performance wise. But there’s been amazing progress. And, automatic dishwashing detergents today are complicated in their formulation, but they’re good. They really work.

GRABER: Great! Dishwashing detergent works, everything is awesome, harmony in the kitchen, right?

TWILLEY: Unfortunately not. I hate to disappoint you Cynthia, but in fact, the real struggle is just about to begin. We may have dishwashers and fancy detergents but we also have disagreements and disputes—big ones—about how to use them. Fortunately we’ve got the correct way to load your dishwasher and so much more after this quick word from our sponsors.

[BREAK]

GRABER: Something that can be a source of strife in a household is whether you should wash the dishes in the sink or throw them all in the dishwasher. We spoke to a guy who loves hand washing dishes so much he wrote an entire book about it called How To Wash the Dishes. His name is Peter Miller.

PETER MILLER: How to wash the dishes was written as an article for a magazine. A little piece that I wrote prompted by my two 30 and 32-year old—I forget what they were, 28 and 30 at the time—kids, where I said to them, neither one of you knows how to wash the dishes. And they looked at me and laughed and said, you wash the dishes. And I said, I know, I do wash the dishes. But I said, you really don’t have a sense or a plan for how to wash the dishes.

TWILLEY: I am going to take a wild guess and say maybe Peter’s kids rolled their eyes at this point. We’re going to get to the prescription for perfect dishwashing in a minute, but first I should declare an interest: I am on team dishwashing machine.

GRABER: So am I, big fan here. And so to be able to really judge whether one option is better than the other, we wanted to understand how dishwashing machines work.

TWILLEY: There’s a lot of videos online where meganerds have put waterproofs go pros in dishwashers to see what’s going on. They’re boring, so I’ll save you the trouble: it’s fundamentally the same mechanism that Josephine came up with, a couple of sets of arms that spray hot soapy water at the dishes.

KINITZ: And, yeah, then the spray arms get turned around by the pressure of the water that is pumped into them.

GRABER: Lotta told us that a big benefit of a dishwasher is that the water is used multiple times. The water breaks food down and blasts it off dishes. It falls back to the bottom, and then that grime gets sieved out of the water, and the newly cleaned hot soapy water is blasted back up on the dishes. This happens over and over again, really quickly, like 10 times per minute.

TWILLEY: That is certainly faster than I wipe soapy water over my dirty dishes in the sink, but is it better? Fortunately, Lotta has tested this scientifically. Which is harder than it sounds.

GRABER: There’s a very specific amount of food and type of food that gets dried on dishes before people are asked to either wash those dishes by hand or put them in a dishwasher. Lotta says it’s standardized.

KINITZ: For example, there are items that should be soiled with spinach that is prepared in a certain way. There are items that are soiled with egg yolk—and only the yolk.

TWILLEY: It’s the details that matter when you’re trying to be scientific about washing up. And so what does science say? Which is better, dishwashing machine or doing the dishes by hand?

KINITZ: It’s clearly the electric dishwasher. So it uses less water, it uses less energy and it also uses less detergent than manual dishwashing.

GRABER: Sorry Peter, but Nicky and I as solid members of team dishwasher, are very happy to hear this. So to start with water, how much better is using a dishwasher than doing it by hand?

SOUZA: Anything from 2013 and on, a single use won’t use more than five gallons. So a single process won’t use more than five gallons of water. If you have an energy star, it’s going to be even less, so 3.5 gallons or less, which—that might sound like a lot. I mean, like, whoa, five gallons, that’s a lot of water. But when you look at hand washing, you know, faucets go about one and a half to two gallons a minute. While they’re on. And so if you did say five minutes of hand washing, and you were on the high end of that, you’re looking at 10 gallons. It’s like twice what it would take to run a full dishwasher.

GRABER: And in five minutes you’re definitely not going to get an entire dishwasher’s load of dishes done. So it’s really not even close. Lotta told us about an experiment where they measured just how much water people were using to hand wash an entire dishwasher’s load of dishes.

KINITZ: And, I think the most spectacular finding they had was one participant who had used like 160 liters of water to clean a whole load of dishwasher items.

GRABER: For those of us who use gallons, that’s about 42 gallons.

KINITZ: So everything that would fit in a dishwasher, they had to wash by hand. And they used running tap water to do it. So they just were used to doing it, like, in that way. And of course that wastes a lot of water.

TWILLEY: And of course you’re also heating up that water, so the more water you use, the more energy you also use.

GRABER: But Peter the dishwashing fan says if he were in a competition with a dishwashing machine, he’d win.

MILLER: If you use the bowl, I would counter that in fact, I could beat the dishwasher. I could make the cleaning more precise, more accurate, and use less activity.

TWILLEY: The bowl is important—this is Peter’s name for his method of hand washing dishes. Which Lotta agrees is the scientifically optimized method if you’re going to wash dishes up by hand.

GRABER: This scientifically optimized method also happens to be the old-fashioned way people always did it, but now with detergent instead of soap.

MILLER: If you’re going to wash the dishes, you need a bowl full of good, soapy water that’s not over-diluted and not messed up by food.

TWILLEY: With that, plus a sponge and a bowl of cold water for rinsing, you are equipped. One by one, working from cleanest to dirtiest, you take a dirty dish, clean it using a sponge in the bowl of hot soapy water, then dunk it in the bowl of cold water to rinse it, and then put it on a rack to dry. Peter is so committed to the hand wash, he often uses his dishwasher as the rack.

GRABER: This method has also been studied. It’s been compared to the dishwasher, but also to other methods of hand washing, like if you were to wash your dishes under running tap water. And it definitely beats the running tap water method, by a lot. But it doesn’t seem to beat the electric dishwasher in terms of water use. Sorry again Peter, but I can’t say I’m sorry about the results.

TWILLEY: Also, no one saves up a full machine load of dishes to hand wash, or uses just one bowl of hot soapy water to do that many dishes. That said, of course, not everyone waits until their machine is full to run it. We just aren’t living scientifically perfect lives.

GRABER: But Lotta told us that on average, studies find that the dishwasher cuts water use by about 70 percent and energy by more than 40 percent. And the dishes even come out cleaner.

KINITZ: The electric dishwasher is better in that, believe it or not. Studies show that people actually do not believe that very often

TWILLEY: So there should be no further discussion here, dishwashing machines for the win. But sadly this is not the end of the debates. In fact, in my household, it is the start of an entirely new one. To pre-rinse or not to pre-rinse, that is the question.

SOUZA: I come from a long background of heavy pre-rinsers, right? Like dishes look pretty clean when they go into the dishwasher. And so that’s how I’ve operated for most of my life.

GRABER: I have discovered upon doing my research for this episode that I come from a mixed household. My mom thought everything should be pre-rinsed, my dad thought that the dishwasher was supposed to do the cleaning. In this case, turns out my dad was right.

SOUZA: In learning from our reviews team here and and their kind of deeper dive into the detergents that are used in dishwashers, they rely heavily on enzymes. And in order for them to sort of cling to plates and bowls and things like that, they actually need some stuff to gain purchase with. And so, like, a little bit of food on there is actually a good thing. They cling to that, and then they’re able to get rid of like, fats and proteins and all these other things that are covering, kind of all of the plates.

TWILLEY: Just to cut your mom some slack, Cynthia, these enzymes weren’t in dish detergent back in our parents’ heyday, and so rinsing made more sense back then.

CLAUSS: I mean, I worked in this area for years. I couldn’t believe it though, after I was retired, that these companies were in their advertising saying you don’t have to rinse your dishes at all. You know. And I said, Oh, no, that doesn’t sound right. You don’t try to scrub the egg yolk off a plate before you put it in the dishwasher? Well, with the formulations they have today. It’s amazing what will come off without rinsing.

GRABER: Lotta says that pre-rinsing actually takes away from all the water and energy savings of choosing to use a dishwasher.

KINITZ: And of course, the worst case scenario would be if you use warm water for that, because then you do not only waste water to pre rinse your dishes, but you would also waste energy to heat the water to do it.

TWILLEY: Okay, so: dishwashers rule, don’t pre-rinse, but here’s a question our parents didn’t have to deal with, and yet there’s a lot of angst about today: the pod. Is it safe?

GRABER: Dishwashing detergents used to all be powder, then you could also buy liquid versions. Then, the first product that was sold as a single dose. One pre-measured amount you put in was called Salvo and it came out in the 60s. And again, like all detergent innovations, it was first for laundry.

CLAUSS: The idea was, well, it’s very convenient. I don’t have to pour a powder into a measuring cup and put it in my clothes washing machine. I just drop one or two Salvo tablets in there. The Salvo tablet was actually rather large, and looked kind of like a hockey puck. Turns out it dissolved about as well as a hockey puck. It was a disastrous experiment in the marketplace, because it didn’t dissolve well enough to work well.

GRABER: The tablets for the dishwasher didn’t work well either, there was usually some detergent left in a clump in the dispenser.

TWILLEY: But then along came something called PVA, or polyvinyl alcohol, which is a kind of plastic that dissolves in water.

CLAUSS: Then it became clear, oh, now, if we’re going to do this, we can seal off separate compartments in the pouch. And then they’ll be released during the wash.

GRABER: This is actually really helpful, they can use different strengths of PVA to make sure that different products get released at different times. And this is great because like for enzymes, they don’t work as well when they’re mixed up with some of the other chemicals in detergents. It’s better to release them separately.

TWILLEY: But surely releasing dissolvable plastic into your dishwater cannot be a good idea?

CLAUSS: The plastic pollution issue is not an issue with polyvinyl alcohol. You know, it dissolves and it’s, it’s pretty benign. And it, it comes out in, in sewage treatment, and it’s really a pretty good actor in terms of the environment. And, once it dissolves, it basically never comes back to particles of plastic that are causing all the problems, you know, that we’re hearing about. So that’s not really the problem.

GRABER: So far that is actually what the studies show. You might have heard of microplastic pollution, bits of plastic that stick around in the water and harm wildlife. But these dissolvable plastics don’t seem to lead to the same issue, they don’t seem to harm wildlife based on the few studies that have been done. So far, there’s not a whole lot of independent research on this. But the EPA has said it’s of lowest concern.

TWILLEY: Onward to the area where I am the undisputed world champion, loading the dishwasher

GRABER: You’re going to have to compete against my partner Tim—

TWILLEY: Listen I’m so good, it’s not going to even be a contest. But according to Lotta everyone thinks that about themselves.

KINITZ: There was one study where people were given a certain amount of, of items that should fit in the dishwasher.

GRABER: They were given 140 items and told to fit as many as they could into the dishwasher. They didn’t know it, but all 140 things could fit in one load at the same.

KINITZ: So a lot of people think they loaded it until it was full, but actually, you could have put more items in.

TWILLEY: In the study, only a third of the participants successfully got all 140 items in. But I would have definitely been among them.

GRABER: You just keep telling yourself that.

KINITZ: So that’s maybe a hard point to improve, because if you’re already thinking you’re doing it right and you already have the feeling that you loaded the dishwasher to the fullest, then you can’t really adjust this habit. But maybe just think about if you arrange the dishes in another way, maybe something could, could still fit in.

GRABER: You have to be open-minded that you do have room for improvement, but that said, there are definitely some hard and fast rules to loading the dishwasher.

SOUZA: Most of them are pretty logical, and make good sense. You know, if you are putting plates next to one another and they’re touching when you put them in, they’re not going to get as clean as if there’s a little bit more space. In terms of top rack and bottom rack, there are some good rules to follow. So it’s going to be a little bit cooler temperature on the top rack. So it’s usually the place for, if you’re watching—you know, you’re washing, plastic containers and things like that, or glassware. It’s going to be a little bit more delicate up there as well.

TWILLEY: The water pressure is typically lower at the top too, so it’s less likely to blast your Tupperware hard enough to flip it over, which as we probably have all experienced is a nightmare because it ends up full of grody water.

GRABER: And a side note about plastics: harder plastics that might say that they’re rated dishwasher safe are fine. But softer plastics like single-use takeout containers shouldn’t go in the dishwasher because the water heat can warp them. And also, some scientists say that they might be weakened enough that when you next put food in them, chemicals might leach out.

SOUZA: When you get to utensils, we actually find you get cleaner results by having the spoon head up and the fork utensils up. And I have a friend who swears by putting all of the spoons in one, all the forks in another, all the knives in another, so that when they’re clean, and she takes it out and she’s loading them back in, it’s just one hand that goes in. And I appreciate that. I think that is really great efficiency on the backend. But: it’s not good practice to put spoons with spoons and forks with forks. Especially spoons because they can nest against one another in the same way that two plates can, and they’re just not going to get as clean in the middle there.

TWILLEY: Spoons cannot be allowed to spoon.

GRABER: But I did wonder if Dan corrected his friend on that very incorrect dishwashing loading technique.

SOUZA: No, I value that relationship too much to try to correct that. You know, and I like—I know, I know for some people this is a hill that they will die on in terms of dishwashers. I am… I’m not that person. I, I, in my mind, it’s like… it’s just amazing to own a dishwasher. That’s kind of my mentality. It’s like, look, if these dishes are going to go in there and they’re going to come out pretty darn clean and we didn’t have to hand wash them? That’s a win. So that’s the place that I am. And I have to do that because if I allow myself to go the other way, I think I would be a horrible person to live with.

TWILLEY: Dan knows the rules but he’s pretty liberal on most points. But he does put his foot down when it comes to things that should never go in the dishwasher.

SOUZA: So obviously really delicate stuff. If you’ve got stemware and sort of beautiful glasses that are best hand washed that you’re going to want to go with that.

GRABER: Keep wood out of the dishwasher, it’ll crack and fade.

SOUZA: A lot of pots and pans will say they’re dishwasher safe, but they’re not, and they can cause kind of pitting. And then nonstick cookware, which is obviously so common these days. That nonstick finish doesn’t do well in a dishwasher. So you’d want to, you’d want to not do that.

GRABER: And finally, there’s one thing that Dan feels particularly strongly should absolutely never go in the dishwasher, and that’s his good, sharp knives.

SOUZA: It has happened to me. I’ve, you know, taken my knives with me to an Airbnb or something with friends and like, I’m like, Where’s my knife? And it went through the dishwasher. Right?

SOUZA: And so, something like that, where it’s really valuable and the dishwasher does a ton of damage to it. Like a prize chef’s knife, I would say that that’s… that’s grounds for divorce. You know, depending on the couple, that can be really bad.

TWILLEY: He’s not wrong. Even though I am on team dishwasher for life, some things really do have to be hand washed. So, hand washing still has a role to play.

GRABER: And even though the dishwasher has changed people’s lives for the better, Susan Strasser said there was something lost. When she was doing research for her book, she heard that getting a new dishwashing machine changed the dynamics in families. This chore had been something for kids to do, for grandparents to do. She read us the interviews from her book.

STRASSER: A lot of elderly women curse the dishwasher. It takes away the one thing that they were useful for. “If we didn’t want our mothers around, at least we would put up with them because they would do what we didn’t want to do. They would do the dishes. But with the advent of the automatic dishwasher, we got rid of our mothers.”

TWILLEY: This seems a little harsh! Grannies have value beyond doing the dishes. But I will say that I can see how it would change family dynamics. As a kid I often did the drying up while my dad washed, and it was a nice chance to chat.

GRABER: Speaking of drying up, the science of whether you should use a tea towel or just let things air dry, we’ve saved that for our special supporters’ newsletter, as well as some hot takes on what you should or shouldn’t do with your dishwashing sponge. Here’s a hint: you should probably switch up your colorful sponges for the beige natural ones because of microplastics. Go to gastropod.com/support to get the scoop.

TWILLEY: And speaking of support, we were originally inspired to make this episode by an email from one of our generous supporters. He had come across a dishwashing technique that shocked and disturbed him

KYLE STEVENS: Hi, my name is Kyle Stevens. I am from Boston, Massachusetts. I remember the first time I visited my husband’s parents in London and seeing that his mom just didn’t really rinse all the soap off the dishes. And I thought this was really strange. And then I found out it’s kind of a common occurrence. And I’d like to know, is that safe?

TWILLEY: Kyle, welcome to my world. As you listeners know, I am British and I grew up in England. And my dad, who as I mentioned typically did and still does the dishes—he also uses this method. He starts by washing the dishes in a tub of hot soapy water, as specified in Lotta and Peter’s optimized method. But he doesn’t rinse them, he just puts them on the rack, with the suds still on them, and then I would wipe those suds off with the tea towel as I dried them. This is how I grew up. And when my American soon to be husband Geoff first witnessed this, he almost had an aneurysm.

GRABER: Dan was also pretty shocked when he heard about this method.

SOUZA: Well, alright. So my first thought is, that’s very water conscious. Like that’s great. You’re not using a lot of water. My second thought is: the British love beer, right? They have a really old school, long held beer culture. Have you ever tried to pour a beer into a glass that has soap residue in it? So soap and bubbles and that kind of stuff is just not going to work well together. You’re going to get some really funky results there.

TWILLEY: To be fair, traditional British ales are pretty flat compared to a bubbly IPA or lager, so maybe the fact that soap residue collapses foam isn’t such a big deal.

SOUZA: But beyond that, like, I just think… I don’t know. I mean, I, if you have a sensitive palate, I just feel like that it’s going to, you’re going to run into a lot of soapy taste in a lot of different foods.

GRABER: I was thinking about this recently because I hand-washed a tea strainer and I thought I got all the soap off and I poured hot water into it like two or three times and I still could taste soap on it. The British method sounds a little suspect to me.

SOUZA: But, I don’t know. If it’s, if it’s a whole nation of people do it and it’s worked for a really long time? Like. I guess more power. But I don’t know. I would, I would really encourage a rinse after that just to get that soap taste off.

TWILLEY: Listen, I don’t think food tastes soapy at my parents house, and honestly neither does Geoff, and researchers say there’s no health risk at all. But that said, soap literally encapsulates dirt particles, so leaving soapy suds on your dish is probably not the best plan. I have Americanized my ways in my own home.

GRABER: And to cut the Brits some slack, just like we cut my mom some slack, the most popular British dishwashing liquid brand, it’s called Fairy Liquid—their ads always show people not rinsing off the suds. If it’s on TV it must be right, right?

SOUZA: I don’t know. There’s… you’re kind of blowing my mind right now [LAUGHING] to be totally honest.

TWILLEY: There is no science that can explain the British.

GRABER: But as you all have now heard, there is science out there that can be used to diffuse basically any of these arguments. But as for Lotta, her spouse doesn’t even bother to argue with her when it comes to anything about dishwashing.

KINITZ: I studied it for like five years, so there’s no dispute on who knows it best. Because of course I know it best.

TWILLEY: I mean, she did get her PhD in dishwashing. That could sound kind of silly, and all these debates might seem kind of low stakes, but Lotta says getting dishwashing right actually does matter.

KINITZ: Because it’s this everyday task that everyone is doing and has to do if you don’t want to end up in a messed up kitchen. So I think it’s really important to see how you can make it as efficient as possible. And if we all could, like, implement these best practice tips, then we could save a lot of resources. And if everyone around the world is doing it, that would add up to a huge amount.

[MUSIC]

GRABER: Thanks this episode to Lotta Kinitz, Dan Souza, Allen Clauss, Susan Strasser, Peter Miller, and our supporter Kyle Stevens, we have links to all their research, websites, and books on our website, gastropod.com.

TWILLEY: And thanks as always to our fabulous producer, Claudia Geib. We’ll be back in a couple of weeks with a brand-new episode. ‘Til then!