Koji, is the fungus, aspergillus oryzae, that grows on grain substrate. It is used in many East Asian cuisines to ferment food. The rich enzymes of koji break down starches and proteins of grains into sugars and amino acids, for making various miso, soy sauces, sake, amazake, etc.
The koji starter I use here for making koji rice is Light Rice Koji Starter from Gem Cultures in US. If you live in Canada, Culture Mother is going to launch those koji starters soon. In Taiwan, you can find various koji starters at Da Shan and 錦池。The whole procedure of making rice koji takes about 3 days.
米麴（rice koji，米こうじ，米糀），是米麴菌（種麴，tane koji，koji starter，學名：Aspergillus oryzae）接種到煮熟的飯粒上，經過一段時間發酵而成。做好的米麴可以再加工做成鹽麴、味噌、豆腐乳、味霖、甘酒、清酒等健康又美味的食物，是很多發酵食品的基本和必需素材。