Fermentation is an indispensable process in miso production. To activate the fermentation process, miso producers in Japan have always used a mold culture. The typical mold for fermentation is koji kin, also known as Aspergillus Oryzae.
Grains such as rice, barley or soybeans are inoculated with koji kin. The mold then propagates and results in the koji culture. Adding kome (rice) koji, the most commonly used culture, to other ingredients and fermenting them produces miso, soy sauce, sake and other fermented foods traditional to Japan, and growing in popularity around the world.
Koji culture has many uses. Not only is it necessary in fermentation, but when combined with other ingredients, it can be used for flavoring, curing and/or preserving foods. One such example of this is shio koji, a mixture of malted rice (koji), salt (shio) and water.
Used in Japan for centuries as a seasoning or ingredient, shio koji has seen resurgence in popularity in recent years with the increased interest in fermented foods. The enzymes contained in shio koji break down proteins to pull out umami flavors and this process also contributes to tenderizing meat and fish. The enzymes also decompose starches to draw out the sweetness from ingredients.
Looking like rice porridge, shio koji takes on a faint sweet flavor for a sweet and salty taste, and has a slightly fermented smell. Depending on the fermentation time and the amount of water, it matures in different forms and textures. It can come in a puree, paste, near solid or even powdered.
Image & text source: Hikari Miso