Traditional Culture of Japan - Portal site of traditional crafts and culture

Making sake: seigiku (making kōji)


In making delicious sake, the most important element is kōji. Kōji is the mold culture that converts rice starch to fermentable sugars.


Kōji is made by propagating kōji-kin mold in steamed rice. The quality of the kōji determines the taste of the final product, the sake.



The importance of kōji
Rice has no sugar content, so in its usual state it will not ferment. For this reason, it is necessary to convert the starch in the rice to sugar. Kōji fulfills this role.


Apart from converting rice starch to sugar, kōji produces various enzymes that are involved in producing vitamins and amino acids. These form nutrients for the kōbo (yeast starter) and give the sake body. The process of making kōji as described here is called seigiku.


Good-quality kōji is regarded as essential for making good sake. However, although it is the most important part of brewing sake, making kōji also happens to be the most difficult and tricky operation in the whole process.


Making kōji
Nowadays, it is possible to produce kōji with a machine. However, because it is so crucial in determining the quality of the sake, it is still sometimes done by hand in the traditional way. One traditional method uses small cases in the course of making kōji.


First, once the rice is steamed it has to be cooled. As a microorganism, the kōji-kin will die if it is exposed to the heat of the rice immediately after it has been steamed. So the rice is cooled to a temperature of 30–35℃.


After that, the rice is transferred to a special room used only for making kōji. This operation is called hikikomi, and the room is referred to as the kōjimuro.



The temperature and humidity inside the kōjimuro are controlled in order to create suitable conditions for the propagation of the kōji-kin. The temperature is around 30℃, the humidity about 60%.


In the kōjimuro, the rice is spread out over a large tub, and kōji-kin spores are sprinkled over the rice. The rice is then alternately stirred and rested. After this delicate operation, the rice is divided up and placed in small cases.


Heat is generated as the mold propagates. For this reason, after the kōji is transferred to the cases, the temperature is adjusted by moving the cases around and stirring the kōji in them. If the temperature rises too high, the kōji becomes weakened.


Following these operations, some 50 hours after the kōji spores were sprinkled on the rice, the silky smooth kōji is ready. At this point, an aroma similar to the smell of roasting chestnuts fills the air. The kōji is now removed from the kōjimuro in an operation known as dekōji.


Kōji determines the quality of the sake
It is said that the quality of a wine is 80% determined by the grapes used. Factors such as terroir and grape variety are regarded as important because the grapes determine the taste and the quality of the wine.


In the same way, kōji determines the quality of the sake. However, in the case of sake, the kōji is something that is produced at each different brewery by human hands. The reason why the flavor and quality of sake depends so much on the people involved in making kōji at the brewery is that kōji is such an important element of sake brewing.


During the period that the kōji is being made, the brewery workers work night and day without sleeping. How the kōji is cultivated has more influence on the quality of sake than the source or variety of the rice, the quality of the water, or the rice polishing ratio.


Even in the case of high-grade sake like ginjō-shu, machines are used in producing kōji. But it is not true to say that when machines are used the entire process can be allowed to run automatically.


There are many things, such as the feel and the aroma of the kōji, that can really only be judged by human senses. While machines can reduce the labor required to make kōji from what was needed for traditional methods, human involvement in the process can never be dispensed with altogether.

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