What Is Koji

Koji is a sweet, fragrant, cultured grain. Primarily used as the first stage in a multitude of dual stage fermentations. Koji is a cornerstone of Japanese cuisine and is the culture responsible for such ferments as; miso, amazake, sake, rice vinegar, mirin and soy sauce. In 2006 the Brewing Society of Japan recognized Koji as the national mold of Japan. For our purposes we primarily cultivate rice koji and will refer to koji as thus. However, koji may also be cultured on other grains such as barley and soybeans. 

The Process

In Japan the written history of the "selective cultivation" of koji dates to over 1300 years ago, with a much longer history in China. The koji making process is one of the longest practiced examples of solid state fermentation. Solid state fermentation involves the growth of microorganisms on and within solid organic materials in the absence or near absence of free water. Similar to the process taking place when cultivating mushrooms.

Growing koji is kind of like farming enzymes. As the culture grows into the grain it releases enzymes that help to break down fats, carbohydrates, and proteins. We then utilize these enzymes in the fermentation process allowing for quick work for our microbial partners.

Rice is soaked and steamed to obtain desired moisture content. 

Then steamed rice is brought into the humidity and temperature controlled muro(koji room) where it is cooled to around body temperature.

When the time is right we inoculate the rice with spores of Aspergillus oryzae and thus begins the life of the koji.


The next 50 + hours is a demanding period of incubation, monitoring, adjusting, and responding to meet the needs of the koji.


When the koji has penetrated to the center of the grain of rice our job is complete.  The koji is allowed to cool and is prepared for its next stage of life.

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