Natto: Japan’s Most Polarising Food
Natto — whole soybeans fermented with Bacillus subtilis natto bacteria — is Japan’s most contested traditional food: deeply loved in the Kanto and Tohoku regions, approached with reluctance or outright refusal in western Japan (Osaka and Kyoto residents have historically regarded it as foreign food), and met with bewilderment by most international visitors who encounter its strong smell, intense umami flavour, and the distinctive web of sticky strings that forms when the beans are stirred. Natto’s combination of high protein, B vitamins, vitamin K2, and nattokinase enzyme has made it a subject of nutritional research; its cultural significance as a breakfast food in Japan’s east is comparable to Marmite in Britain — a defining regional taste that separates insiders from outsiders.
Production
Natto is produced by steaming soybeans, inoculating them with Bacillus subtilis natto spores, and incubating at 40–45°C for 15–24 hours in shallow containers (traditionally rice-straw bundles, which naturally harboured the bacteria; now small polystyrene containers). The fermentation converts the soybeans’ proteins, producing the characteristic strings (formed by poly-glutamic acid polymers created by the bacteria) and the ammonia-forward aroma that intensifies during fermentation. After incubation, the natto is refrigerated for 1–2 days of maturation, which develops the flavour further. Traditional natto made in rice straw (wara natto) has a stronger, more complex character than the commercial polystyrene-pack variety.
Mito: Japan’s Natto Capital
Mito in Ibaraki Prefecture is considered the cultural capital of natto — the city’s agricultural region supplies a significant portion of Japan’s natto soybean production, and local natto varieties (including okame natto, Japan’s best-selling brand) are produced throughout the region. The Natto Museum (Natto Museum) in Mito documents the food’s history and production; the annual Natto Festival in January celebrates the food with cooking demonstrations and consumption events. Restaurants in Mito serve natto-based cuisine including natto maki (sushi rolls), natto toast, and the local specialty of natto served over thick udon.
How Natto Is Eaten
The standard preparation: open the polystyrene pack, discard the sauce and mustard sachets or mix them in per preference, stir vigorously 50–80 times (the strings lengthen with stirring, which is considered texturally desirable), then serve over hot rice with the optional additions of green onion, raw egg yolk, soy sauce, and karashi mustard. The stirring develops the strings; more stirring is said to produce better natto. Natto is eaten warm or at room temperature; it is never heated significantly, as heat destroys the nattokinase. Regional variations include hikiwari natto (chopped, finer-textured), kotsubu natto (small bean variety), and natto served in miso soup in some Tohoku households.
The East-West Divide
Japan’s natto divide roughly follows the old Tokaido highway as a cultural boundary. Kanto and Tohoku (Tokyo and north) consume natto daily; western Japan (Osaka, Kyoto, Hiroshima) has historically resisted the food, with surveys consistently showing that western Japanese residents are far less likely to eat natto regularly. The divide reflects different breakfast food traditions — western Japan’s breakfast culture centred on lighter, more delicate tastes while eastern Japan’s colder winters and agricultural tradition embraced the warming, protein-dense natto. Contemporary food distribution and media have blurred the regional boundary somewhat, but it remains a real and culturally discussed phenomenon.