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How to make Natto, fermented soy bean

Fermentation and food culture

Shoyu, miso, sake, milin are Japanese key ingredients. These are all made by the work of Aspergillus oryzae (koji mold). Lactic acid bacteria is used for making tsukemono pickles, hay bacillus (Bacillus subtilis) is used for making tempe or nattou, and Penicillium is for cheese.

Wine and cheese well suit for bread (made by wheat/rye), and natto, tsumemono and sake go well with rice. Various types of crops and bacterias which are suitable for its climate and soil have been selected and domesticated since ancient time.

The combination of main crop and native germs have influenced traditional food cultures.

History of natto, fermented soy bean in Japan

Formally, the first historical record of natto dates back to 11th century, but it is said that natto already existed in Yayoi period (300 BC–300 AD), when beans started to cultivate in Japan. The ingredients are simple; only boild bean and straw, or even any kinds of wild grasses are possible to ferment soy beans. It is said that natto became popular among worrier, since it is handy to bring soy beans to battle field, wrapped by straw, then soy beans got naturally fermented. Natto became commercial products in Edo period (1603 – 1868), and spread all over Japan.  Especially, natto produced in Mito in Ibaragi prefecture is popular. People in the eastern part of Japan more often eat natto, compared to the west.

Merit of natto

Why fermented foods became widespread in Japan? One of the advantage of fermentation is that harvested crops can be preservable for longer term, especially in rural area, crops can be harvested a lot at one time, and less in winter season. It is required to stock food and prepare for off-season. Also, fermentation adds much more nutrition value as well. The other advantages of fermented soy beans are; It contains NattokinaseIt is rich in protein, Vitamin K, B2, B6 and E, mineral, and fiberEspecially, in Japanese cuisine, soy bean products such as tofu, miso, natto are major protein sources. 

How to make natto

It is fermented with Bacillus subtilis, which grows under the aerobic condition. It is very interesting to make various types of natto in combination of diverse beans and plants, from which natural bacteria can be harvested. It should not be always "soy", but it is possible to make natto by using kidney beans, peas, black beans, azuki beans, and even rice, or other grains as well!

In Japan, we use rice straw to harvest natto bacteria, however, in other asian countries, various plants are used, for instance, banana leaves are used in Thailand, and in Myammer, it is believed that a certain kind of fern can make the best natto.


  1. Soak beans for 6-24 hours depending on variety and temperature 

  2. Steam soy beans or other types of beans and peas 

  3. Inoculation: Wrapped with straw or other leaves 

  4. Keep it warm for 24-48 hours 

  5. Keep it in fridge for 24 hours (the taste will be better after leaving one more day)

Variation of nattou

<Shape of beans> 1. Grain shaped 2. Dried 3. Grinded


①Natto bacteria  

②Aspergillus   Touchi in China, Daitokuji natto in japan

③Tempe   Indonesia

<Starter> straw, fern, cheak, banana leaf, fig leaf

<geography> Laos, Thai, Myanmer, India, Bhutan, Nepal, China, Korea, Japan

In Korea, natto is called as "jiang (sause) from Qing dynasty", and it is dried. It is also reported that it was once eaten during war time, since it is made quickly and can be preserved for long time. This type of dry natto without stickiness can be found also in a part of Japan.

Many natto in Asia is not used as grain, but mostly grinded into paste with chili, and dried.

Influence of plants for natto flavor and stickiness

When natto bacteria eats protein, it produces glutamic acid and fractose, which combined to be muchin, sticky compounds. Bacillus bacteria can survive under high temperature unto 100 celsius, however, most active temperature is approximately 40 degree.

Comparing the tastes, the flavors, stickiness, and texture are different dependent on the variety of beans and plants we used.

Protein ritch soybeans showed more stickiness, and starch-ritch pea or cowpea showed less threads, however, peanuts and gingko nuts also turned to be natto (sorghum millet did not change). In addition, softness of original boiled beans also affected the results. Hard boiled beans and soft boiled beans are different in terms of stickiness.

Personally, I like the flaber of rice straw. For some Asian ethnic group, it is reported that ferns are considered their most favorite flavor, and when it is not available, they only use straw.

1. Banana leaf (Musa spp.)

Flavor★★★ Stickiness★ We wrapped beans by banana leaf and newspaper, though, the beans got dried without enough moisture. No stickiness, but it tastes good.

2. Fern

Flavor★★ Stickiness★★★ Compared to cowpea, soy beans showed more stickiness.

3. Bamboo

Flavor★ Stickiness★★★ The most sticky natto is the one with bamboo leaf. Cowpeas tend to be less sticky but with the combination of bamboo leaf, it got more sticky.

4. Rice straw

Flavor★★★ Stickiness★★ This may be due to my Japanese DNA, I feel straw flavor is the best!

5. Makomo wild rice (Zizania latifolia)

Flavor★★ Stickiness★

It is too dried and not so much sticky, also not so strong flavor.

How to use natto

If you do not like the strong smell of natto, you can also use it as a seasoning.

Natto shoyu

blend following ingredients; natto, salted koji, amazake, soy sauce, chili, seaweeds

Natto dressing for salad

blend with; natto, leek, radish, ginger, lemon, vinegar

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