Bacillus subtilis – NBRC 13169

Bacillus subtilis 

Nattō is made from soybeans, typically nattō soybeans. Smaller beans are preferred, as the fermentation process will be able to reach the center of the bean more easily. The beans are washed and soaked in water for 12 to 20 hours to increase their size. Next, the soybeans are steamed for 6 hours, although a pressure cooker may be used to reduce the time. The beans are mixed with the bacterium Bacillus subtilis, known as nattō-kin in Japanese. From this point on, care must to be taken to keep the ingredients away from impurities and other bacteria. The mixture is fermented at 40 °C (104 °F) for up to 24 hours. Afterward the nattō is cooled, then aged in a refrigerator for up to one week to allow the development of stringiness.

In Natto-making facilities, these processing steps have to be done by avoiding incidents in which soybeans are touched by workers. Even though workers use B. subtilis natto as the starting culture which can suppress some undesired bacterial growth, workers pay extra-close attention not to introduce skin flora onto soy beans.[11] To make nattō at home, a bacterial culture of B. subtilis is needed. B. subtilis natto is weak in lactic acid, so it is important to prevent lactic acid bacteria from breeding. Some B. subtilis natto varieties that are more odorless are usually less active, raising the possibility that minor germs will breed. Bacteriophages are dangerous to B. subtilis. Historically, nattō was made by storing the steamed soybeans in rice straw, which naturally contains B. subtilis natto. The soybeans were packed in straw and left to ferment.