Koji (Aspergillus oryzae) — the mold cultivated on rice, barley, or other substrates to produce a dense matrix of digestive enzymes — is the foundational technology of Japanese and Korean fermentation and the most important single fermentation organism in the food world. Koji produces the enzymes that make soy sauce, miso, sake, mirin, doenjang, and gochujang; it is the organism that converts starch to sugar for sake fermentation; and its proteases are what transform proteins into free amino acids for garum and koji marinades. Understanding koji is understanding the entire East Asian fermentation tradition.
**Koji growth conditions:** - 30–33°C for the initial phase (spore germination and hyphal growth) - 28–30°C for the later phase (enzyme production — reducing the temperature slightly shifts the mold's metabolism toward enzyme production rather than growth) - Humidity: 80–95% — the spores require moisture for germination; the later growth produces heat that must be managed - Time: 44–48 hours from inoculation to mature koji **Inoculation:** - Steamed rice (or other grain/soy) mixed with tane koji (spore powder) — approximately 0.1–0.2% spores by weight of the grain - Mixed thoroughly and placed in a shallow container in the humidity chamber **The mature koji:** - Covered with white mycelium, with a sweet, floral, chestnut-like aroma - Should smell of fresh mushrooms and sweet grain — any ammonia or sour smell indicates contamination - Test: the rice grains should be fully colonised, sticking together in clumps from the mycelium, but not fully broken down **Temperature management:** - Heat generated by the mold's metabolism must be managed — the core of a dense koji bed can reach 40°C+, killing the mold. The bed must be mixed or turned regularly during the growing period.
Noma Fermentation