Ibaraki Prefecture — Mito City as symbolic capital; production distributed across Kanto and Tohoku
Ibaraki Prefecture is Japan's largest natto-producing region, accounting for approximately 40% of national production, with Mito City as the symbolic capital of natto culture. Natto — fermented soybeans with Bacillus subtilis natto — is one of Japan's most polarising foods: intensely aromatic (ammonia and isovaleric acid), viscously stringy (the poly-gamma-glutamic acid strands), and deeply savoury with an earthy funk. The Mito natto origin legend attributes its creation to Minamoto no Yoshiie (11th century), whose army supposedly discovered fermented soybeans in rice straw after leaving cooked beans wrapped in straw bundles — Bacillus subtilis natto is naturally abundant in rice straw and warm fermentation occurs spontaneously. Traditional production: small (kotsubu, small bean) or large soybeans are washed, soaked 12 hours, steamed until fully cooked but intact, then inoculated with Bacillus subtilis natto starter, placed in straw rope or modern polystyrene trays, and fermented at 40–42°C for 16–24 hours. The fermentation time and temperature precisely determine the stringiness level, ammonia intensity, and surface texture. Premium artisan natto (Azuma Foods, Takayanagi Foods) is sold in straw bindings (wara natto) — the straw imparts earthy, grassy notes absent from tray-packed versions. The correct eating technique involves vigorous stirring (100 stirs is the traditional number cited) to develop the maximum poly-glutamic acid strings before adding tare (soy sauce and mustard packet) and green onion.
Deeply funky, ammonia-edged, earthy, intensely savoury soybean — shocking on first encounter, addictive to those who understand its nutritional depth and character
{"Fermentation temperature of 40–42°C is critical — too cool produces under-fermented beans with insufficient Bacillus activity; too hot denatures the enzymes","100 stirs develop the poly-glutamic acid strands to maximum length and produces the fullest flavour integration with the tare","Wara (straw) natto has a distinct earthy, nutty flavour from the straw's Bacillus natto population and the grassy volatile compounds it contributes","Natto should not be heated above 50°C — the active Bacillus subtilis natto probiotics are destroyed above this temperature, and the distinctive texture changes","Mustard (karashi) in the natto tare serves a flavour function — the pungency cuts through the ammonia-forward aroma and balances the fermented intensity"}
{"Cold natto (refrigerator temperature) has a more cohesive string structure — letting natto sit at room temperature for 5 minutes before serving makes it slightly more fluid and fragrant","Wara natto from Mito shops has a deeper, more complex flavour than tray natto — the straw's Bacillus population includes wild strains alongside the cultured starter","Natto over very hot fresh rice is the essential combination — the heat from the rice slightly warms the natto, releasing additional aromatic compounds","Premium natto pairing: Ibaraki's Ozaki wara natto with Akita Koshihikari rice, a raw egg yolk, finely sliced negi, and a touch of wasabi — the wasabi's allyl isothiocyanate cuts through the ammonia"}
{"Skipping the stirring step — unstirred natto lacks the string development and the tare does not fully integrate, resulting in an unbalanced flavour","Adding soy sauce before stirring — the correct order is stir first to develop strings, then add tare, then stir again to incorporate","Heating natto in a microwave to 'improve the flavour' — heat destroys the Bacillus natto enzymes and changes the texture from sticky-stringy to sticky-gluey"}
Japan Natto Industry Cooperative Association; Japanese fermented food scientific literature