Bowl of koji rice next to a wooden box filled with rice
Elevate Your Home Cooking With Japanese Fermented Rice
By Dainius Vaitiekunas
Japanese household staples like soy sauce, mirin, and miso all contain koji, a type of fungus that grows on grains such as rice, barley, or soybeans. You can make rice koji at home to enjoy its sweet fruitiness and umami richness and transform your dishes in so many ways.
Koji is an excellent addition to meat marinades, usually in the form of koji salt, which can be made by mixing koji with water and salt and letting it ferment at room temperature for seven days. Koji's unique sweetness also goes great with cooked salad and salad dressings and is the main ingredient in the sweet, low-alcoholic drink amakaze. 
Rice koji is traditionally made by steaming the rice, dusting it with koji spores, and placing it in an incubator for a couple of days. If you're just dipping your toes in the world of fermentation or don’t have an incubator, try using a dried koji rice starter that has already been propagated and dehydrated — simply pour lukewarm water over it and let it sit for a few hours to activate.