page_title: Nattō
section_title: Production process
hierarchical_section_title: Nattō / Production process
context_page_description: Nattō is a traditional Japanese food made from soybeans that have been fermented with Bacillus subtilis var. natto. It is often served as a breakfast food. It is served with karashi mustard, soy sauce, and sometimes Japanese bunching onion. Nattō is often considered an acquired taste because of its powerful smell, strong flavor, and sticky, slimy texture. Within Japan, nattō is most popular in the eastern regions, including Kantō, Tōhoku, and Hokkaido, and a 2009 survey revealed that 70.2% of Japanese people find the taste pleasant, and others who may not find the taste of the food pleasant still eat it for health benefits.
context_section_description: 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 six 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 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 nattō-making facilities, these processing steps have to be done while 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 on to soy beans.
  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 closer to 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.
caption: Soybeans in a plantation
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