The process of turning rice starch into sugar is called saccharification. In order to turn the starch into sugar, sake brewers use a type of fungus called koji-fungus, specifically Aspergillus oryzae, which is a safe variety of mold. Not only does the koji-fungus turn starch into sugar, it also turns the proteins into amino acids.
- Koji refers to steamed rice that is treated with koji-fungus. This step is essential for the creation of sugars from the rice grains which are then fermented to yield sake.
- About 20% of the polished rice (mushi mai) is used to make koji.
- In the koji making process, the brewer begins by taking the steamed rice into the koji making room (koji muro) where it is spread out into a thin layer. The temperature of the koji muro is kept at approximately 30 oC and 50-80% humidity.
- When the steamed rice has cooled to 30 oC (86 oF), the koji-fungus is sprinkled on the rice and kneaded evenly into the rice grains. Careful control of the temperature is important because the koji-fungus grows best around 36 oC but becomes inactive above 45 oC.
- There are two types of koji fungus:
- The sohaze-style koji fungus grows all over the grain, producing lots of diastatic enzymes and vitamins. It is highly effective at breaking down rice and results in a robust fermentation, producing sake with a strong body.
- The tsukihaze-style koji fungus grows in spots on the grain. The enzymatic activity is moderate, but poor in vitamin and fatty acid content. The fermentation isn’t as active and produces light-flavored sake. Ginjo and daiginjo sake are producing tusing tsukihaze-style koji.
- The koji rice is kept warm by bundling it for a time, then spread out and mixed so that the grains do not stick together and finally put into trays (or a machine) which creates the uniform conditions of temperature and moisture needed for the koji kin to act upon the steamed rice
- This step is the most crucial part of making sake as the amount of fungal spores, water content of the rice and temperature greatly influence the final product.
References:
1. Japanese Sake, How is Sake Made?
2. Harper, Philip, The Book of Sake A Connoisseur's Guide, Kodansha International, 2006.
3. Sakaya, Sake Making Steps
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