Koji is a culture which is made up of multiple complex organisms, including mold, bacteria among others. In humid Japan, koji occurs naturally. It generates an enzyme, which causes fermentation that brews the sake, soy sauce, shochu (Japanese distilled liquor), vinegar, and creates miso and pickles.
In order to make koji, rice, barley, soy beans and other cereals are cooked first. Then the appropriate koji spores are mixed into the cooked cereal. When they are kept at a certain temperature range for a period of times, cereals turn to koji.
Only a handful of makers produce rice koji in the United States. However, in Japan, other types of koji products are available. Different koji is used for different purposes.
If you can’t find koji in your area, you can order from the following online shops. Please note that koji and koji starters are different.