Traditionally attributed to Minamoto no Yoshiie (11th century, Tohoku campaign); scientific Bacillus subtilis isolation by Dr. Sawamura Seiichi 1905; modern standardised production Taisho era; Mito as natto capital formalised 20th century
Natto (納豆) is fermented whole soybeans produced by inoculating cooked soybeans with Bacillus subtilis var. natto, then incubating at 40°C for 18–24 hours until the bacteria produce the characteristic sticky polyglutamic acid strands (the 'neba-neba' stickiness) and the complex flavour compounds. The smell—ammonia-adjacent, pungent, sometimes described as strong blue cheese—is the most discussed characteristic; it is produced by the bacterial breakdown of amino acids into volatile compounds including pyrazines and dimethylamine. Mito City in Ibaraki Prefecture is Japan's most famous natto production centre, though the Kanto region consumes the majority of Japan's natto (Kansai has significantly lower per-capita consumption, a regional taste divide as marked as any in Japanese food culture). Quality indicators: the beans should be uniformly coated in sticky strands without drying or breaking; the smell should be present but not overwhelming; the beans should still have some textural resistance (not completely softened to mush). Eating ritual: natto is typically stirred vigorously 50–100 times before eating (the stirring incorporates air and develops additional sticky strands), then seasoned with the included mustard and tare (soy-mirin sauce), optionally with additional spring onion, raw egg yolk, or karashi. Over rice is the canonical breakfast serving. The health claims for natto—nattokinase's fibrinolytic properties, vitamin K2 content, probiotic bacteria—are the most studied of any Japanese fermented food, making natto the subject of significant nutritional science interest.
Pungent, ammonia-adjacent, nutty bean with complex bacterial flavour compounds; mustard and soy seasoning integrate and moderate; over rice the combination creates a complete high-protein breakfast with complex fermented depth
{"Bacillus subtilis fermentation operates at 40°C—above 45°C the bacteria are killed; below 35°C the fermentation stalls","Stirring before eating (neba-neba activation) is functional, not ritual—mechanical action develops additional polyglutamic acid strand formation","The mustard (karashi) included in commercial natto packaging cuts through the ammoniac notes and stimulates appetite—do not skip it","Natto should be eaten at room temperature, not cold from the refrigerator—cold natto is less sticky and more pungent; brief warming (15–20 seconds microwave) moderates both","The characteristic flavour compounds develop most intensely in the final hours of fermentation—over-fermented natto (>30 hours) becomes excessively ammonia-dominant"}
{"Premium natto (Hoshi brand, for example) uses larger hikiwari (roughly crushed) beans that provide a different texture experience from standard whole-bean natto—less sticky resistance, more bean-to-strand surface area","Natto pasta (natto mixed with pasta, butter, shiso, and nori) is one of Japan's most successful yo-shoku adaptations—the fatty pasta medium distributes the natto flavour without overwhelming it","Fresh-made natto (within 24 hours of fermentation completion) has the mildest flavour and most active bacterial culture; as it ages (refrigerated), the flavour intensifies toward the ammonia note"}
{"Eating natto directly from refrigerator—cold dulls the desired stickiness and emphasises the ammonia note; brief warming significantly improves the eating experience","Skipping the stirring step—under-stirred natto has less developed strand network and less interesting texture","Adding too much soy sauce—natto already contains protein breakdown products with salt-like flavour; over-seasoning makes the flavour flat and excessively salty"}
Tsuji Shizuo, Japanese Cooking: A Simple Art; Japan Natto Producers Cooperative technical documentation; NHK Gatten natto food science series