It’s the pungent smell, the distinctive flavour, and the slimy texture that is either putting people off or enticing to some. Nattō is a traditional Japanese breakfast food. It needs to be stirred with soy sauce, mustard, and green onions to produce sticky strings before being served over a bowl of hot rice.
Nattō is being produced by first washing and soaking soybeans in water from 12 to 20 hours. Then the soybeans will be steamed for about 6 hours, then a bacteria (Bacillus subtilis) is introduced and mixed in to the cooked soybeans. The soybeans need to be fermented at 40°C for up to 24 hours, cooled, then refrigerated for up to a week to develop stringiness.
There are many theories as to how nattō would have come about in the first place, but the underlying hypothesis is for the cooked nattō to have ended up nesting in a bed of rice straw that had rested for some time before being discovered. Rice straw was plentiful back in the days in Japan, when it was being used heavily as floor mats, as horse feed, as roofs for houses, as materials for straw bags or bales, for sacred braided ropes, and to make sandals etc. Rice straw happens to contain a truck-load of the nattō bacteria naturally. It may appear as an accident that nattō came about, but with the abundance of rice straw in the environment, the naturally occurring bacteria in rice straw, and a diet rich in soybeans, nattō is destined to come to life.