How is Sake Made?---The Koji

The Koji
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.

The next step in the sake making process is the selection of yeast. Stay tuned and come on the sake making journey with me!
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