Koji Fermentation

Koji fermentation is the technique, central to Japanese and other East Asian cuisines, of cultivating the mold Aspergillus oryzae on steamed grain, such as rice, wheat or barley, or on soybeans, to create a fermentation starter. Spores of the mold are inoculated onto the steamed substrate, which is then held for two to three days at around 30 degrees Celsius in high humidity to let the mold grow through it. As it grows, the mold's enzymes break down the substrate's starches into glucose and its proteins into amino acids such as glutamic acid, producing the sweet and umami flavors characteristic of koji-fermented foods. Different strains of the mold are cultivated for different products: yellow koji is used to make soy sauce, miso, sake, rice vinegar and mirin, black koji is used for the distilled spirit awamori, and white koji is used to make shochu.