Obsessed: Getting Funky With Natto

"What does it taste like?"

It's the hardest question to answer about natto, the sticky Japanese breakfast staple made from fermented soybeans. It usually follows hard on the heels of, "What's that smell?" and, "Why does it look like that?" and it never fails to stump me. There really isn't anything like it in Western cuisine, and between its goopy texture and powerful aroma (one of my American uncles likens the smell to very old, never washed gym socks), it falls into the same love-it or hate-it category as foods like tripe, stinky tofu, and durian.

But for those of us who love natto—and in Japan, that's damn near everybody—its sliminess and its funky smell trigger a Pavlovian response, as if the slimier-looking the beans and the funkier their smell, the better their flavor will ultimately be. If dashi is the pristine embodiment of umami distilled from the sea, natto is the earth's muddier and darker equivalent. It has a beany taste, of course, and it's a little bitter. But it also exhibits the alkalinity of a fresh pretzel, along with some of bass notes of browned foods, as if it were toasted or roasted, even though it is not. In Japan, it's most commonly eaten with rice, but it's also a worthy mix-in for soba, and one of the best snacks for my money at a combini, or convenience store, is a natto sushi roll. I also recently discovered that natto goes perfectly with pappadum.

While it isn't unusual to find natto-philes, it is a little odd to run across someone in America who has devoted themselves to its manufacture. For one, it is a stinky process; for another, natto would seem to have a limited market given the comparatively small size of the Japanese population in this country. I first met Ann Yonetani while doing research for our ramen-slurping video; she happened to be delivering some natto to one of the ramen chefs at the time. Yonetani had just ended her first full year of producing natto full-time through her company, NYrture, and she claimed that her natto was tastier than the stuff you can buy at Japanese grocery stores.

I was skeptical, until the moment I tried it. It has a fuller, more complex flavor than the stuff I'd been buying here, which always seemed an insipid echo of the kind my family buys in Japan, despite the fact that I buy the same brand. (Yonetani attributes the difference to the effect of freezing the beans.)

Yonetani and her husband, Zach Perlman, have now both abandoned their careers in science (she was a microbiologist, he was a biophysicist working in pharmaceuticals) to produce natto full-time, and they do most of their business by delivering their product in person, to a clientele that she claims is only about 10% Japanese. I sat down with her over lunch recently to ask her about it all.

Name: Ann Yonetani

Day job: Natto maker

Website: NYrture

Facebook: NYrture New York Natto

Instagram: @nyrture

Do you remember when you first tried natto?

I don't actually recall the first time I had it, but natto is a traditional Japanese food, and I'm Japanese-American—I was born and raised here, but my parents are from Japan. I think I pretty much only ate natto when I would go to Japan. We'd go pretty often; when my grandparents were still alive, we'd go every other summer. I was probably just offered natto very early on, and I would eat what I was served as a kid. I may not have been the biggest fan at first, but I grew to enjoy it as part of everyday Japanese cuisine.

When did you start thinking about making natto?

I'd been really passionate about cheese for many years, so I traveled to several different farms and went through some cheese-making courses, and actually had the fantasy of becoming a cheesemaker. But, seeing as I lived in Manhattan and have a life here, it really wasn't a very realistic dream to have. Then I realized, well, natto is essentially a vegetarian cheese—the Japanese cheese.

I traveled to Japan in 2014 and spent the summer there with my kids, eating all the varieties of natto I could find. I found a very old natto maker in Tokyo, Hiromitsu Amano; he's the oldest natto producer that's still working in metropolitan Tokyo. It's a fifth-generation family business, so they've been doing it for hundreds of years. I basically called them up and explained that I was a food science professor in New York and I was very interested in the process of making natto, and asked if they would be willing to have me come and learn, and they very generously let me do that.

I spent a few days with them. I got to see the process, and talked with Amano about natto history and his family's experience. I learned an incredible amount. Then, when I came home to New York afterwards, I started fiddling around with it at home.

So you come back from Japan and know how to make natto. Did you start doing it just as a hobby? Just to eat it?

Yeah, just to see if I could do it. Of course, I did have the thought, "Hey, maybe I can start making natto professionally." But in the beginning, it started with just seeing if I could do it at all. The very first batch...I think the first batch was probably not very good. If the fermentation fails, then basically your boiled beans don't change much. They taste like nothing—very bland boiled soybeans. But I kept doing it, and I got it to be pretty consistent. In the meantime, I was accumulating all this natto, which was more than my family could consume, so I started giving it out to friends, and they told their friends, and their friends told their friends. I guess that was the first lightbulb of inspiration for producing it commercially: "Wow, there are a lot of people out there who are interested in this food."

But your own interest stems, at least in part, from your professional background as a microbiologist, right?

Yeah. Well, once a microbiologist, always a microbiologist. I did a PhD in microbiology, and I worked in biomedical research for 15 years. Several years ago, I started teaching food science at the New School. Just basic science, but diverse topics all related to food—so the biology of farming, of GMOs, of nutrition, metabolism, food ingredients, food additives, fermentation; the chemistry of meringue, or ice cream, or cheese, or bread, like what happens on a molecular level, and the chemistry that transforms food during cooking. People are passionate about food as a topic these days, and I found that food was a powerful platform through which to talk to people about science.

As a microbiologist and food-obsessed person, I've always been particularly interested in fermented foods and the biology and chemistry behind fermentation. Natto is a natural leap for me because of my heritage. But then I started reading about the biology of it and about all of the medical science that's started to delve into all of its potential health benefits, and it blew me away. Its properties, and effects on human biology—there are so many different things about natto that have pretty credible and large bodies of evidence to back them up.

So how do you make natto?

First, you either boil or steam soybeans. I steam them. I think all professional natto makers steam them because if you immerse any food in liquid, you're going to lose a lot of flavor and nutrients. You also will sort of disturb the integrity of the beans if you boil them—it kind of makes the outside of the bean ragged, which won't look nice. Then, while the beans are still very hot, they're inoculated with Bacillus subtilis, which is a very common soil-dwelling bacteria. The beans have to be hot because Bacillus subtilis is a spore-forming bacteria. Most bacteria don't do that; they simply grow and divide, and grow again and divide. They just do binary fission. But a small subset of bacteria have an alternate path to reproduce. So under conditions of stress, basically, if there isn't enough food around or something, or just if conditions are bad, they can turn on this alternate life cycle and decide to form spores.

Is that important for natto-making?

It's probably why you can make this food safely. Spores are basically designed to be like seeds that can survive with no requirements. They're kind of dead, really, until they encounter favorable environments again, so they're very hardy, they're very resistant. They can last for, I don't know, decades, maybe longer, with nothing, no input. They're also very resistant to high temperatures—like, you can boil spores for an hour, and they're completely fine. Like, 99% still viable. So that's why when you steam the beans, you can add this bacteria in spore form immediately, when the beans are piping-hot, under conditions where most other bacteria in the environment will not survive. When the beans are cooked, they're essentially sterile, and then you can just dump on a lot of Bacillus subtilis, which doesn't mind the heat, and just completely saturate the beans with this one bacteria.

After the beans are inoculated, they're incubated for about a day at quite a high temperature, above 100°F (38°C), and at high humidity, as well. They need a lot of moisture. At home, I used a yogurt maker: basically a little enclosed box with a water tray on the bottom, placed above a heating element.

I read somewhere that natto is an odd fermented food, in that it is an alkaline ferment instead of an acidic ferment, like kimchi or dill pickles. Can you talk about that?

It's just the nature of the bacteria. Soybeans aren't alkaline, and that's all that's in the environment. This natto contains nothing but steamed soybeans and Bacillus subtilis, but the mixture goes from a neutral pH to a pH of around 9 by the end. I don't use pH as an indicator—alkalinity is just a by-product. I suppose one could, but it's much easier to assess the fermentation visually. I'm pretty sure making the mixture alkaline has no effect on the growth rate of the bacteria.

What happens after incubation?

At least with my process, it goes into a refrigerator. I think it has to age for a few days before it really starts to develop the right flavor. There's some further breakdown of proteins—everything doesn't come to a grinding halt in the fridge. There's still a very low level of bacterial activity going on, so, to some extent, there's some fermentation, but there's also just some passive chemistry that's happening, too, because the fermentation has done a lot of breaking down of the various soybean components. Once broken, the proteins release more glutamates and amino acids, and the natto develops a stronger umami taste over time.

But every producer has their own detailed methodology, and they differ in terms of exactly what temperature or what range of temperatures they use, for how long, the moisture levels, the type of bacterial strains. There's a variety of strains that are available, and each one has slightly different characteristics. They have different impacts on the natto product, so different companies are particular about which kinds they like to use. So far, I've been sticking with one strain, but I do plan to experiment with some others. I think, to be honest, the differences between strains are quite subtle. For example, it's said that there are strains now that produce less smelly natto. I believe less smell goes hand in hand with the natto being somewhat less sticky. There are strains that ferment the beans faster; there are strains that are better for the very small-bean natto, as opposed to the larger-bean nattos. But the differences are not huge, I would say.

In Japan, because this is such a developed industry, there are food scientists who devote all of their time to studying the effects of all these slight variations in the basic method. And actually, there's a very serious natto competition each year, where the 200-some producers of natto all compete. I think there are 40 judges, so it's very political; it's like a consortium event, and it takes apparently decades of training and experience for these guys to become qualified to be natto judges. It's like the wine world, really. So there are subtle differences between the varieties that those with less experience are just in the dark about, but there are differences.

Can you talk about the different varieties of natto that exist? What makes them different?

Each of the hundreds of natto producers in Japan makes a unique natto product. There's a range of soybean sizes used and differences in texture and appearance. For example, there's hikiwari natto, where the beans are all chopped up, and beyond the regular brown natto, there's green and black natto. Many Japanese pick their natto brands based on the tare, or sauce, that comes with it. In some regions, people prefer a sweeter tare; others like their tare saltier. For a tiny producer like me, providing a tare is a whole other project to take on. In Japan, most natto companies don't even make their own tare; they source it from tare companies.

What is it that gives natto its sliminess?

Neba-neba is the Japanese word that refers to the uniquely sticky, slimy, gooey texture that natto is known and loved for. Natto's stringy "special sauce" is a product of the bacterial fermentation, a biofilm produced by the bacteria to protect itself and to allow it to move around. It's a living environment, like pond scum. (Maybe you shouldn't write that.) It's composed of amino acid polymers, polyglutamate, which is a chemical way of saying it's made of strings of pure umami taste, which increases as the natto ages. The strength of the sauce's stickiness is basically a measure of how strong and happy the probiotic bacteria are. It's also where all the good stuff produced by the probiotic bacteria resides. It's absolutely the best thing about natto.

Some people refer to natto as a "superfood," and earlier you mentioned that there has been some convincing research about its potential health benefits. Can you expand upon that?

If there is any food on earth that I think truly deserves that overused title, it's natto. My initial interest in its health benefits was focused on its probiotic properties, because fermented foods and probiotics are an exploding area of interest, both in food circles and in science circles. Bacillus subtilis has been found to be one of the good guys in the human gut microbiome, meaning that in a healthy human gut, it is one of the species that's commonly found, but it's completely absent from any food that's commonly available in America.

One very valid argument against probiotic foods is that the vast majority of the bacteria that you eat are going to be killed by the hellhole of acid that's in your stomach. So there is some benefit to eating probiotic foods, obviously, but it's not like it's a straight shot—you're losing 99.9% of them in your stomach. A lot of foods have just the lightest add-in of probiotic bacteria, and you're just not going to get anything out of that. The thing about natto is that this bacteria, which we want to get through, is sporulating, and those spores, I'm sure, are going to be able to go through the stomach without much problem.

I've actually gone to Harvard and have used microscopes there to examine what's going on in my natto over time—fresh, a few days old, a month old, even two months old—and there are living bacteria in there, and plenty of spores, as well. Natto's particular probiotic bacteria could be especially powerful because of those spores, but more actual scientific data to back up that idea needs to be generated.

Can you give an example of a specific health benefit that has some research behind it?

There's evidence that nattokinase, an enzyme that's produced by this bacteria, has an effect on cardiovascular health, in that it breaks down clotted material in the bloodstream. Actually, nattokinase has been sold for years as a medicinal supplement. You can find several brands of it in any Whole Foods. It comes in pill form. It used to be purified from natto, or bacillus cultures. I think now it's such a big industry that they've found alternative ways to produce it, but its source is natto.

The bacteria also produce vitamin K, specifically vitamin K2, during the fermentation, and vitamin K2 is turning out to be a very interesting micronutrient that many people are probably not getting enough of in their diet. It seems to be good also for cardiovascular health, as well as bone health, because vitamin K2 is basically something you need in your bloodstream in order to get calcium from your diet out of the bloodstream and into your bones.

There are other sources of vitamin K2. Natural gut bacteria produce it—Bacillus subtilis is one of those—but other fermented foods, like cheeses and salami, have it, too. But the level of K2 in natto versus cheeses and cured meats is an order of magnitude higher—fifteen- to twentyfold more K2 in natto. If you're vegetarian and you don't eat those foods, then there's virtually no source available to you. I think natto is a powerful food that provides a lot of things that could be missing in vegetarian and vegan diets.

There's a lot of potential, with a lot more strong scientific evidence, than most superfoods that are out there. This isn't science that's being funded by natto companies. This is just pure academic research.

You said earlier that foods fermented with Bacillus subtilis aren't commonly available in America. Beyond natto in Japan, what other foods are fermented with the bacteria?

There are a number of other bacillus-fermented foods in East Asia, South Asia, and Africa. The Koreans have a number of different soybean ferments that are also bacillus-based, but the most common one is doenjang, which is more or less natto, although the method of fermentation makes a product that doesn't have the sticky, gooey aspect natto does because it's a dried-down paste.

Depending on which region of Africa you're in, the name varies, but the most common name is dawadawa, which is also a paste, but historically it was a ferment of locust beans, a common protein source in central and western Africa.

What's the difference between your natto and the stuff in Styrofoam containers you can buy in Japanese grocery stores?

My natto is a fresh, never-frozen product, whereas all of the natto imported from Japan is frozen during export, with no exceptions. In Japan, all natto is fresh, and the natto there only has a shelf life of about a week. It's such a massive market and people eat it on such a daily basis that that's not a problem. My natto, in theory, can last a very long time in the refrigerator. Like cheese, I think it has a certain window of time where it's pleasant to eat, after which it just starts getting a little too funky. I think that window is three months. I have eaten my natto at six months old, but it's pretty pungent. Real sharp. It could be fine for some people, but the majority of folks would find it too much, so I usually tell people to eat it within two months. And the big point about the freezing and thawing is that they decimate most of the health benefits, and I'm certainly finding that most of the people who are buying my natto are really into it because of the health benefits that they've heard about.

What's your favorite way to eat natto?

The experience of trying to popularize this largely unknown food and educating customers, who are always asking for serving suggestions, has pushed me to explore creative, nontraditional ways to enjoy it. If you check out my Instagram, I can't help myself, every time I eat out, I have to put natto on stuff. I actually find it much more interesting and much more accessible if you think of it as a new ingredient that you can combine with whatever foods you like.

This interview has been edited and condensed for clarity.