Japan — Ibaraki Prefecture primary production, nationwide consumption
Natto — soybeans fermented with Bacillus subtilis var. natto — has been covered in its general production principles elsewhere, but the regional variation within natto culture deserves specific attention: the differences between Ibaraki's classic hikiwari (fine cut) natto, Hokkaido's larger bean varieties, Mito's production using specific straw wrapping traditions, and the diverse flavour applications that extend natto beyond its morning rice context represent a richer picture than the single-entry overview provides. Ibaraki Prefecture (especially Mito City) is Japan's natto heartland — producing approximately 60% of domestic natto using soybeans from North America (imported) and Hokkaido (domestic premium). Mito's most traditional natto was historically produced by wrapping soybeans in rice straw, which naturally harboured Bacillus subtilis on its surface, creating a fermentation environment that varied seasonally and batch-to-batch, producing complex, unrepeatable flavour. Contemporary natto production uses pure Bacillus cultures in styrofoam containers for consistency, but artisan producers (including several in Mito and Fukushima) still produce straw-wrapped natto (wara natto) with noticeably more complex, earthy flavour. Three styles by bean size: kotsubu (small bean — most popular nationally, milder flavour), hikiwari (finely minced beans — stronger flavour, used in specific preparations), and okidai (large bean — firm texture, preferred in some regions). Flavour additions that define regional character: dried kombu (Hokkaido influence), myoga and shiso (Kansai), karashi mustard and negi (standard Tokyo style), and the development of modern natto-based preparations (natto pizza, natto pasta, natto spring rolls).
Pungent, ammonia-edged, deeply savoury, slightly sweet — kotsubu: milder and more accessible; wara natto: earthy and complex; all styles share the fundamental Bacillus fermentation character
{"Bean size affects flavour intensity: smaller beans (kotsubu) produce milder natto; larger beans ferment differently and have firmer texture","Straw-wrapped vs container: wara natto (straw) has more complex, earthy character from multiple Bacillus strains present in straw; container natto is more consistent","Stirring to develop strings: the characteristic strings (polyglutamic acid produced by Bacillus) develop with vigorous stirring — traditionally 100+ stirs before serving","Seasoning after stirring: mustard and tare should be added after the strings have fully developed — adding before stirring disrupts the string development","Temperature matters: natto served slightly warm has more active flavour than cold; allow to come to room temperature before serving"}
{"Stir the natto 50-100 times before adding the tare packet — this is not an exaggeration; it genuinely develops the string texture and integrates the fermented soybean proteins","For guests new to natto: start with kotsubu (small bean, milder) rather than large bean or hikiwari — ease into the flavour","Natto with finely sliced fresh okra: the okra's own mucilage combines with natto's polyglutamic acid strings, amplifying the characteristic texture in a way that is surprisingly harmonious"}
{"Adding seasoning before developing the strings through stirring — this produces inferior string development and textural integration","Serving straight from refrigerator without allowing to temper — cold natto has muted flavour and texture"}
Preserving the Japanese Way — Nancy Singleton Hachisu; The Art of Fermentation — Sandor Katz