Natto Production Bacillus Subtilis Fermentation

Japan (Kanto region, particularly Ibaraki — Mito; Edo period development from earlier soybean fermentation traditions)

Natto (納豆) is produced through the fermentation of whole soybeans by Bacillus subtilis natto — a naturally occurring bacterium traditionally transmitted from straw (wara) wrapping, now commercially propagated as pure starter cultures. The production process: soybeans are soaked overnight, steamed until fully soft, inoculated with B. subtilis natto spores, and fermented at 40–42°C for 18–24 hours in humidity-controlled chambers. During this period, the bacteria produce nattokinase enzyme, poly-glutamic acid (responsible for the characteristic stringy, viscous threads between beans), vitamin K2, and a distinctive ammoniacal-earthy aroma. The finished natto has a sticky, stringy surface with a complex bitter-earthy flavour and the characteristic fermented soybean aroma that divides Japanese opinion. Regional variations are substantial: Mito in Ibaraki Prefecture is the acknowledged capital of natto culture, producing a full spectrum from hikiwari (crushed, more spreadable) to large-bean premium natto from specific heirloom soybean varieties. Premium 'naturally fermented' wara-natto (straw-wrapped in rice straw) is the artisan form using traditional wild fermentation. Natto eating technique matters: the conventional preparation involves 50–100 vigorous stirring motions to maximise the viscous threads before adding seasoning and raw egg yolk.

Complex bitter-earthy-ammoniacal with strong umami; acquired taste profile; threads add viscous sticky texture; raw egg yolk and soy seasoning tames and rounds