大豆と豆類

Soy and legume ferments form the densest cluster of geographically-defined fermented foods in East Asian culinary tradition. The technical foundation is consistent: soybeans (or other legumes) cooked, inoculated with one or more koji-type molds, and aged with salt for weeks to years. The variations across the category — Japanese miso vs Korean doenjang vs Chinese doubanjiang — are produced by differences in mold organism (Aspergillus oryzae vs wild mixed cultures), substrate (rice vs barley vs soy itself), salt level, aging time, and inoculation method (controlled koji vs wild surface fermentation).

The Japanese tradition uses controlled inoculation with Aspergillus oryzae (or Aspergillus sojae for shoyu) on a starch substrate (rice, barley, or soybeans themselves for the unusual hatcho miso). The mold develops on the substrate over 36-48 hours, producing copious proteases (which break down soy protein into amino acids, producing umami) and amylases (which break down starch into sugar, providing sweetness and energy for fermentation). The resulting koji is mixed with cooked soybeans and salt, then aged anywhere from 2 weeks (saikyo) to 3+ years (hatcho).

The Korean tradition uses meju — soybeans cooked, formed into bricks, dried, and exposed to ambient air for 2-3 months. The wild surface fermentation involves Aspergillus, Rhizopus, Bacillus subtilis, and lactic acid bacteria, producing a more complex and 'funky' flavor profile than Japanese miso. The dried meju is then brined for 6-12 months, producing both ganjang (Korean soy sauce, the liquid) and doenjang (the paste). Gochujang adds fermented chili paste to the meju-based foundation.

The Chinese tradition includes both controlled-koji and wild-fermentation traditions. Doubanjiang (Pixian, Sichuan) uses outdoor sun-exposure fermentation of broad-bean-and-chili paste for 1-3 years with daily stirring — a labor-intensive technique that produces the foundational paste of Sichuan cuisine. Douchi (fermented black soybeans) and furu (fermented tofu) round out the Chinese soy-ferment family.

The Indonesian tradition gives us tempeh, produced by Rhizopus oligosporus binding split soybeans into a solid cake — structurally unlike paste-based miso/doenjang. The Japanese tradition also gives us natto, produced by Bacillus subtilis var. natto on whole steamed soybeans, producing the famously stringy and aromatic breakfast food.

The category is unified by its dependence on enzymatic protein breakdown — the proteases (from koji or wild molds) hydrolyze soy protein into peptides and free amino acids, producing the intense umami that characterizes the category. The salt levels (8-18% depending on tradition) preserve the long aging periods. The geographic-protection traditions across the category are some of the strongest in fermentation: Hatcho (Aichi), Pixian (Sichuan), Phu Quoc (Vietnam, though for fish sauce), and Sunchang gochujang (Jeolla) all have legally-defined production regions.

Sandor Katz's Art of Fermentation and the more specialized work in Koji Alchemy (Umansky and Shih, 2020) have brought the technical depth of this category to Western home practitioners over the past 15 years.