Japanese Natto Fermentation and the Bacillus subtilis Culture Tradition

Heian-period Japan (traditional legend traces to 11th century samurai Minamoto no Yoshiie); Ibaraki/Mito as commercial centre from Edo period; industrial production from 20th century

Nattō (納豆) — fermented soybeans produced through Bacillus subtilis var. natto fermentation — is one of Japan's most polarising foods and one of its most nutritionally significant. The sticky, stringy, pungent soybean product is a breakfast staple throughout Japan (particularly Eastern Japan and Tohoku), eaten mixed with mustard (karashi) and tare sauce over rice. Production involves cooking soybeans until soft, inoculating with B. subtilis natto bacteria, and fermenting at 40–45°C for 16–24 hours in small straw containers (warastutsu) or, in industrial production, polystyrene packs. The straw-fermented natto (waranatto) represents the traditional production method — Bacillus subtilis naturally inhabits rice straw, and the historical practice of wrapping cooked soybeans in straw bundles was the discovery mechanism for natto fermentation. The fermentation produces nattokinase — a potent fibrinolytic enzyme with demonstrated cardiovascular benefits — along with menaquinone (Vitamin K2), beneficial to bone density and arterial health. This nutritional profile has generated international interest in natto as a functional food. Natto's flavour profile — ammoniacal, deeply savoury, fermented — is an acquired taste; the stringiness (hikimono) is the signature textural element, produced by polyglutamic acid and fructan polymers generated during fermentation. The more the natto is stirred before eating, the more pronounced the stringiness — serious natto enthusiasts stir 50–100 times to achieve maximum hikimono development.

Strongly savoury, ammoniacal, yeasty, umami-rich; stringy texture with soft bean interior; the flavour is often described as blue cheese-like in its intensity — powerful, deeply fermented, acquired