Koji mold use in the production of sake dates back to the Nara period (early 8th century) and has been a crucial ingredient in the brewing process ever since. At its core, koji is essentially steamed rice with mold spores cultivated into it. The main function of this “magical mold” is to provide the enzyme that breaks down the starches in rice into sugars that can be fermented by the yeast cells, which then gives off carbon dioxide and alcohol. It is incredibly important to note that sake production would be impossible without koji. Historically, there have been three different types of koji mold that have been used during the brewing process:
- Aspergillus oryzae (yellow koji mold),
- Aspergillus awamori (black koji mold), and
- Aspergillus kawachii (white koji mold).
Selecting the right mold and preparing it the proper way are crucial factors for brewers to decide when choosing the type of sake they will be creating. In modern sake/shochu production, yellow koji mold is by far the most popular and available option to breweries in Japan, with characteristics of strong fruity aromas and low levels of citric acid.
Also known as seigiku, koji production is at the heart of the sake brewing process. Cultivated in a special room called the koji muro, the entire procedure lasts about 40-45 hours, and at the end of the operation koji looks like rice with a small amount of frosting on each grain. In present day Japan, yellow koji mold is produced everywhere, while black koji mold is found in Okinawa and white koji mold is manufactured in Kyushu. As stated earlier, each mold gives sake a different flavor, and unlike the more popular yellow koji mold, white and black koji mold produce rich strong flavors with high levels of acidity. When I first started researching koji mold, I was curious to see if shochu required different kinds of mold than sake did, but I was surprised to find out that both sake and shochu use the same three molds. Overall, koji mold is a crucial part of every single brewing process in Japan.