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Brewing process

Koji making

The heart of the brewing process.

A portion of the steamed rice is sprinkled with koji mold and taken to a warm, humid room called a kojimuro, where the koji mold is cultivated for two days. As the koji grows, it forms a fine gray fuzz around each kernel of rice. This rice, called komekoji or simply koji, is an essential ingredient for making amazake, or sweet sake, which goes into the pre-fermentation mash. Amazake provides the sugar energy that the yeast uses during fermentation to create alcohol. The quality of the amazake ultimately determines the flavor profile of the resulting sake, so it is no overstatement to say that the koji from which amazake is derived is at the very heart of the Brewing process. For this reason, Masumi makes all of its koji by hand. The kurabito apply a combination of science and hard-earned skill to raise each batch of koji with all the care you'd lavish on a new-born baby.

1. Seeding the rice

A 20% portion of the rice steamed each day is sprinkled with finely powdered koji mold and taken to the kojimuro (cultivation room) where it is put in a long, shallow tub called a toko. This is the beginning of the koji-making process, which lasts two full days and nights. The seeded rice is tightly wrapped in fine cloth and is left to cultivate in the high temperature and high humidity of the kojimuro.

2. Mixing

In the afternoon that the rice is seeded, the batch is hand-mixed to spread the heat evenly.

3. The peak

4. The middle stage

5. The final stage

On the morning of the second day, the koji is moved from the toko tub into a special box called a tana. The koji is now said to be at its peak. In the afternoon the koji is spread thinly on a heated table to aid in evaporation. Great care is taken to avoid sudden rises in temperature. At about 7:00 in the evening this process is complete and the koji is given its final handling.

6. Bringing out the koji

On the morning of the third day, the steaming koji is taken out of the kojimuro (cultivation room). The brewers then spread the koji in long swirling lines on trays. The perfectly cultivated koji is now ready for the next day's brewing.