Koji plays an important role in sake making. So, what is Koji? Koji is in the form of a powder and the strain is maintained on the rice. First, the powder is scattered over cooked rice and the Koji spores will grow for three days. The mixture of rice and Koji is stirred constantly to promote the action of enzymes. After the process, rice is literally penatrated by koji. There is no sake without Koji, sake is not the only beverage in the world using koji. There are a couple of others throughout Asia, like miso and shoyu, but the brewing methodologies are different.
Rice contains starch, a macromolecule composed of sugar chains which cannot fermented as-is, it is essential to separate the chain into smaller sugars. This is done through a process called saccharification. Koji, a fungus classified in the type of aspergylus oryzae (filamentous fungus, or mold ) is spread on the rice, develops and releases amylases , enzymes capable of transforming starch into simple sugars . These simple sugar can be fermented into alcohol by the action of yeast.