Natto​— Japan’s Unique Soybeans

By Awake! writer in Japan

Does the thought of eating fermented, stringy soybeans sound appetizing? Likely not! But natto​—fermented steamed beans—​is a popular food in Japan. Indeed, it is estimated that each year more than 110,000 tons of soybeans are used to produce 220,000 tons of natto.

ACCORDING to legend, about a thousand years ago the warrior Minamoto Yoshiie found and tasted boiled soybeans that had been left on straw and had fermented. That was the discovery of natto. It is believed that by the end of the Edo period (1603-1867), natto had become a regular part of Japanese cuisine in some areas.

How is natto made? In the past, bundles made from rice straw were filled with steamed beans and then stored in a warm, humid environment. This resulted in fermentation by Bacillus natto, a bacterium that lives in rice straw. During fermentation, proteins and glucide contained in the soybeans decompose, generating the distinctive natto strings, which can stretch up to 20 feet [6 m]!

Nowadays, natto is mass-produced in automated factories, where steamed soybeans are sprayed with the ideal amount of Bacillus natto. The beans are then transferred to small containers by machine. A conveyor moves them to storage, where preset temperature and humidity levels allow the beans to ferment and mature. After packaging, the natto is ready for market.

Natto has a distinct odor that some find repugnant. But the stringy beans are nutritious. During fermentation, vitamins B₂ and K and such minerals as iron, calcium, and potassium are created. In addition, natto contains enzymes that aid digestion. Nattokinase, an enzyme that dissolves blood clots, has also been found in natto.

Natto strings may have other uses besides food. For example, they are processed into fiber, biodegradable plastic, and resin. The natto resin is water retentive.

Fermentation produces heat as well as agents that suppress other bacteria. Thus, when made properly, natto lasts a long time. In one experiment, natto bacilli were cultivated with enteropathogenic E. coli O157, which is known to cause fatal food poisoning. The E. coli O157 died. Still, it is recommended that natto be kept in a refrigerator and consumed within a week or so because its taste will gradually change. When the fermentation process goes too far, the soybeans fully dissolve and a sharp ammonialike odor develops.

Many people eat natto the traditional way​—seasoned with soy sauce. Some prefer to add mustard or minced scallions, while others add seaweed or an egg. Natto goes well with hot white rice. It can also be served with spaghetti, Japanese noodles, and even soup. Some enjoy it on buttered toast. When served with rice, it is best to mix the beans thoroughly. The more you mix them, the more strings will be produced.

Natto is gaining greater popularity as its nutritional value becomes more widely known. In fact, odorless natto is now on the market, welcomed by those who have avoided it because of the smell. By all means, try natto. a You too can discover Japan’s fermented, stringy soybeans!

[Footnote]