During Week 1 of the COVID-19 stay-at-home order here in Chicago, I supported a small business by having beer delivered from a local craft brewery.

I started a jigsaw puzzle in Week 3 and gave in to the sourdough baking boom in Week 4. Netflix and HBO only lasted me until Week 6, when I added Hulu to my subscriptions. And, in Week 9, in a moment of boredom, curiosity and gastronomic nostalgia, I made nattō (fermented soybeans) at home.

Like many people familiar with the controversial dish, I originally had a hate-hate relationship with nattō. I ate it only when it would have been rude not to, until the principal at the school where I was teaching told me a story of its origin, saying, “Nattō is samurai no niku (the meat of the samurai).”

According to his story, warriors would roll their soybeans in bamboo leaves, shove them in their pockets and forget about them. After battle, when they’d worked up an appetite, the beans had conveniently rotted into a sticky, smelly and, yes, delicious mess.

Inspired by this tale, I decided to add nattō to my diet, and eventually grew to love the dish.

While this origin story is likely apocryphal, the nattō production process is as simple as “set it and forget it.”

Fermentation fever: Three grams of nattōmoto spores is enough to inoculate 30 kilograms of nattō. | DANIEL MORALES
Fermentation fever: Three grams of nattōmoto spores is enough to inoculate 30 kilograms of nattō. | DANIEL MORALES

I cook Japanese-style breakfasts somewhat regularly, but I’ve always limited myself to miso soup and salmon. The downtime I’ve had during the COVID-19 pandemic helped me realize I had the equipment to reproduce the fermented bean dish on my own.

The most difficult part of the process in the United States is acquiring the bacteria cultures required for the ferment. You can either use fresh nattō to seed a new batch, or purchase Bacteria subtilis (vari. natto) from retailers.

If you’re in Japan, Yuzo Takahashi Laboratory sells a variety of nattōmoto spore options from ¥2,700. The Asian markets near me did not have frozen nattō to use as a seed batch, unfortunately, but Amazon did have a vial of the Takahashi-brand spores, which arrived within 24 hours and cost $13.99 (about ¥1,500) for 3 grams, enough to inoculate 30 kilograms of nattō, the equivalent of over 600 single-serving packs!

Once you have the bacteria, the only other things you really need are water and soybeans. And time, of course. The process requires nearly three full calendar days from start to finish, but fortunately it no longer involves stuffing your pockets full of soybeans.

Recipe: How to make homemade nattō (fermented soybeans)


100 grams soybeans

Nattōmoto spores or one fresh pack of nattō

A few milliliters of sterilized water

First, cook the soybeans. I recommend starting with 100 grams. Soak the beans overnight, and then either steam them in a pressure cooker for 40 to 50 minutes, or boil them for several hours. The cooked beans should be slightly softer than al dente but not pasty.

From this point on, it’s essential that you maintain an extremely sanitary cooking space. You’ll need to inoculate the beans with the starter, but you don’t want to accidentally grow anything else. Disinfect all bowls, spoons and containers in a pressure cooker with a quick steam or clean them with a diluted bleach solution (15 milliliters of bleach per 4 liters of water).

Once you have the cooked beans in a sanitized container, use the special scoop provided with the spores to add a 0.1 gram spoonful of nattōmoto to a few milliliters of sterilized water that you’ve heated in the microwave, swirl it up and then stir it into your cooked soybeans with a sanitized spoon. (Alternatively, you can take a quarter of a pack of fresh nattō and mix it into your cooked beans.)

Loosely cover the container with plastic wrap and hold it at around 37 degrees Celsius for 24 hours. Many Japanese use a kotatsu heater or a reptile heater for this purpose. With an Instant Pot electric pressure cooker, no plastic wrap is necessary, and you can use the yogurt setting to maintain the perfect temperature, just make sure to put your soybeans in a glass or stainless steel container.

After 16 hours, you’ll notice a whitish film develop on the beans, as well as the typically pungent, footy odor. At 24 hours, the beans should have slimy strands drawing them together. Transfer the nattō to a plastic container, refrigerate it overnight and it’s ready to eat.

Serve nattō over rice with a side of miso soup for a satisfying breakfast. For authentic flavors, stir in a dollop of karashi mustard and a small amount of soy sauce. If you’re outside of Japan, S&B Foods’ Oriental Hot Mustard powder is relatively easy to acquire and makes karashi with a seriously spicy kick.

For a less traditional, but equally delicious, approach, you can slice half an avocado over the nattō and top it all with a mix of wasabi and soy sauce.

In line with COVID-19 guidelines, the government is strongly requesting that residents and visitors exercise caution if they choose to visit bars, restaurants, music venues and other public spaces.

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