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How is sake made?




Sake, as well as wine and beer, is made through fermentation of yeast. Fermentation is the process whereby yeast (a kind of microbes) produces alcohol and carbon dioxide from sugar.
Sake is made from rice, rice koji, and water. Neutral alcohol may also be added. Here is an outline of the process of making sake.

Kome-koji (Koji made from rice grain)

Koji mold (a variety of Aspergillus) is called the national mold of Japan. Koji is used for making a variety of traditional Japanese foods. Beside sake, koji is used to make shochu (Japanese liquor), soy sauce, miso, and vinegar. Strains of koji have been commercialized since the Muromachi period (1333- 1573), which is much earlier

 

 

 

The first step in making kome-koji is to cool down the steamed rice, and bring it into a koji room. Then, the rice is spread out on a long table called a toko, and "koji seeds" (spores of koji-mold) are scattered over it. Then, the mass is mixed well so that the spores adhere evenly to the steamed rice. After that, the rice is heaped up and covered with cloth to keep the temperature and humidity of rice constant. The scattered spores germinate and extend their hyphae. During this process, the temperature of koji rises from the heat generated by the koji's metabolism. If the temperature were to rise too high, the koji would be damaged. In order keep a suitable temperature, moisture, and the growth of hyphae uniformly, the koji is mixed and the pile is spread out again.

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As time goes by, white areas called 'haze' extend across the surfaces of the rice. Approximately two days after the rice is placed in the koji room, the koji-making is finished.

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The koji extends hyphae not only on the rice, but also into the rice grains. While the koji mold is growing on the steamed rice, it produces enzymes. Though the enzymes cannot be seen, they have a very important role in the making of sake. The enzymes from the koji convert the starch in the rice into sugar.
Yeast needs sugar to make alcohol. Starch has longer molecules made of sugar and cannot be directly converted to alcohol by yeast.
That is, yeast does not have an enzyme to digest starch. When the koji is added to the main mash, its enzymes convert the starch to sugar.
The yeast can then produce alcohol from that sugar. Koji and yeast make a great team!

 

 




National Research Institute of Brewing