Natto Stirring Technique Fermented Soybean Regional Varieties

Japan; Kanto tradition centered on Mito Ibaraki; Bacillus subtilis traditionally from rice straw wrapping

Natto (fermented soybeans) is among Japan's most divisive foods—beloved by Kanto residents who eat it daily, avoided by many Kansai and foreign palates due to its pungent fermentation ammonia smell and extremely sticky, viscous texture. The Bacillus subtilis bacteria produce characteristic poly-gamma-glutamic acid (PGA) polymer threads during fermentation at 40-45°C for 18-24 hours, creating the distinctive strings (hikimono—'pull things') that have become natto's defining visual characteristic. Traditional natto wisdom holds that vigorous stirring (200-400 rotations) before eating increases viscosity and enhances flavor through mixing oxidation. The number of stirs is debated by enthusiasts, with the general principle that more mixing produces more flavor complexity. Natto is eaten over rice with a raw egg yolk, mustard (karashi), and soy sauce as the standard Tokyo breakfast. Regional varieties differ significantly: Mito (Ibaraki) is considered the home of natto with small-grain ibaraki soybeans; hikiwari natto uses chopped rather than whole beans; Kyoto hikiwari natto is smaller and milder. Outside Japan, the strongest barrier is the ammoniated smell, but experienced natto eaters often find it as comforting as cheese.

Pungent ammoniated fermentation; sticky viscous texture; deep bean umami; softened by soy, mustard, egg yolk