Cooking with Koji

Koji is a live culture, specifically rice or grain inoculated with the mold Aspergillus oryzae, and it is the quiet backbone of Japanese cooking. It is what turns soybeans into miso, rice into sake, and wheat into soy sauce. For a home cook, koji is a fast track to deep savory flavor. Rub it directly onto fish or meat a few hours before cooking and enzymes break down proteins, tenderizing the surface and amplifying umami. You can also buy shio koji (a salted paste) or shoyu koji (a soy based version) as ready to use seasonings that add complexity to marinades, dressings, and sauces.