The traditional method is to wrap steamed soybeans in straw, which is soaked in boiling water at 100 degrees to sterilize and keep it at 40 degrees Celsius for one day. Bacillus subtilis (Bacillus subtilis), which is commonly found on the straw, is heat-resistant due to its ability to produce spores, so that the sterilization process is not disrupted, and high-temperature cultivation is fast enough to inhibit other strains of bacteria and make the soybeans produce a sticky filamentous substance after fermentation, and this sticky appearance comes mainly from the ingredient glutamic acid. comes from the glutamic acid in the ingredients, which is thought to be the source of natto's delicious flavor.

In the late 20th century, high-quality straw was harder to come by, and it was often sold in Styrofoam or paper containers. Therefore, the modern way of making natto is to use steamed soybeans mixed with artificially cultivated natto mushrooms and put them directly in a container to ferment them, and some foods other than soybeans can also be made into natto.

Modern factory-made natto

Modern factory-made natto

In the case of sake brewing, if the rice used as raw material is inadvertently contaminated with the natto bacteria, the yeasts required for brewing are inhibited by their rapid reproduction. Natto must not be present in the sake brewing premises, but other fermented foods may be similarly affected, so the process requires careful attention.

Natto bacteria are weakly acidic, and can hinder the production of lactic acid by lactobacilli. Technically, we have developed natto with a weaker odor, but the use of natto strains with lower viability can easily create room for other bacteria to proliferate. In addition, the natural enemy of the natto bacteria is the phage virus that parasitizes the bacteria. When the phage begins to act, it reduces the activity of the natto bacteria and may cause other bacteria to begin to multiply, so you should avoid consuming natto that has exceeded its shelf life.

How to eat

Traditionally, natto is mixed with soy sauce or wasabi (the boxed natto sold in department stores is usually made with light soy sauce and yellow wasabi) until a silky texture appears, and then eaten on top of white rice, which is called natto rice. Some people also mix natto with various ingredients such as raw eggs, green onions, minestrone, daikon radish, and shiba fish. In Hokkaido and Tohoku, natto is sometimes mixed with sugar. There is also a creative way to eat natto with mayonnaise. If you add the sauce without mixing it, it will become too watery and lose its consistency, while green onions and wasabi suppress the pungent odor of "natto ammonia". Those who are not used to eating natto think it is rotten boiled soybeans.