Shio koji is a traditional use of koji, the ancient mold that gives us soy sauce, miso, fermented bean paste, and sake. It is made by combining rice koji (cooked rice that has been inoculated with koji spores and then dried), salt, and water and letting the mixture ferment for about a week, during which time it develops a sweet, fruity, slightly funky aroma. Shio koji is primarily used as a marinade. Because it is rich in protease enzymes (which break down proteins) and amylase enzymes (which break down starches), it can transform many foods. In our Koji Fried Chicken, it turns the chicken incredibly savory and tender. In our tests on fish, we found that shio koji firmed and gently cured the filets. Makes about 1 quart.
We prefer using a plastic food storage container for this recipe, but any medium (1-quart or more) food-safe container will work. There are a few options for buying rice koji. Some well stocked high-end supermarkets carry it, but for the majority of us, online is the best option. You can purchase our favorite brand here. [Ed. Note: this koji suggestion is from America's Test Kitchen.]
1. In medium saucepan, heat water to 140 degrees F/60 degrees C. Combine hot water, koji, and salt in lidded container and whisk until salt is dissolved, about 30 seconds. Cover with lid and let ferment at room temperature until mixture is thickened and smells sweet, fruity, and slightly funky, at least 7 days or up to 14 days, stirring once per day. After initial fermentation, store in refrigerator for up to 6 months.
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