ricekoji

Ricekoji is a fermentation starter produced by cultivating the mold Aspergillus oryzae on steamed rice. The mold grows on the surface and through the grains, creating a white, powdery coating as it metabolizes the starches and proteins in the rice. The resulting product, known as rice koji, contains enzymes such as amylases and proteases that convert starches to sugars and proteins to amino acids, enabling controlled fermentation.

Production involves steaming short- or medium-grain rice, cooling it to around 30°C, and inoculating with spores of A. oryzae (koji-kin). The mixture is kept in a warm, humid environment with periodic mixing for 24–72 hours to promote even growth. After incubation, the rice is dry enough to prevent further mold growth and can be used immediately or stored under refrigeration or freezing for longer-term use.

Ricekoji is a fundamental starter in many traditional Japanese ferments, serving as the primary saccharifying agent in sake, miso, and soy sauce. It is also used in making amazake and certain faster-fermented products. The enzymes produced by the mold break down starches into simple sugars and proteins into amino acids, contributing sweetness, body, and depth to the finished product.

Safety and handling: ricekoji is a living culture and should be prepared in clean conditions to minimize contamination. Inhalation of spores can irritate the airways for some individuals, and people with mold sensitivities should handle it with care. Proper storage—refrigeration for short-term use or freezing for longer-term use—helps maintain quality.

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