Natto

Natto is one of the most distinctive ferments in the world — whole steamed soybeans inoculated with Bacillus subtilis var. natto and incubated warm for about a day, producing beans coated in a stringy, sticky polymer (polyglutamic acid and fructans, mostly) with an aroma frequently described as ammoniacal, cheesy, or feet-like depending on the describer's relationship with the product. It is a Japanese breakfast staple in eastern and northern Japan, an acquired taste for many westerners, and microbiologically unique among major commercial ferments.

The organism is the key. Bacillus subtilis — sometimes called the hay bacillus — is a soil bacterium common globally and is dramatically different from the molds and yeasts that drive most fermentation. The natto variant produces natto-kin — a strain selected for its ability to bind soybean proteins into the characteristic stringy mucilage that defines the product. This polymer (polyglutamic acid) is what produces natto's distinctive neba (stickiness) and the strings that lift off the spoon when natto is stirred.

The traditional Japanese practice of vigorously stirring natto with a spoon before eating — 50-100 times, traditionally — is functional rather than decorative. The stirring develops the neba further, breaks the polymer into shorter chains, and changes the mouth-feel and aroma. Stirring matters; natto eaten unstirred is editorially a different (and less developed) product.

Natto's nutritional profile is remarkable: very high in protein, exceptionally high in vitamin K2 (specifically the MK-7 form, where K2 is in short supply in Western diets), high in vitamin B2, contains nattokinase (a fibrinolytic enzyme that has attracted research attention for cardiovascular effects), and provides significant probiotic Bacillus subtilis content. The K2 content makes natto a serious nutritional consideration for K2-deficient populations, though the texture and aroma remain barriers for non-Japanese consumers.

The traditional method used wild Bacillus subtilis from rice straw, which inhabits the surfaces of dried straw and rapidly colonizes warm cooked soybeans wrapped inside. Most modern home and commercial production uses purified natto-kin starter (powder or concentrated culture) for consistency. Both methods are valid; the wild-straw method is closer to historical practice and tends to produce slightly more variable but potentially deeper-flavored natto.