What is koji?

The moldy basics:

Koji (also spelled kōji or kouji) is traditionally a cooked grain, most commonly rice, that has been inoculated with Aspergillus oryzae, the fermentation culture known as koji mold.

Koji has been famously cultivated in Japan for thousands of years for its uniquely transformative powers. Koji enhances food by producing enzymes that transform nutrients like starches and proteins to create tasty sugars and amino acids.

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Why is koji so special?

Culture and Tradition
Koji is the foundation of Japanese cuisine and was declared Japan's "official national fungus" in 2006. Koji has a millennia-long history in the island nation reflected in their most popular food staples: miso, soy sauce (shoyu), sake, and so much more!
The process of making rice wine and fermented bean paste using molds was first documented in the 4th century B.C. In 725 AD the Japanese book Harima no Kuni Fudoki ('Geography and Culture of the Harima Province') first mentioned koji outside of China and described that the Japanese produced koji with fungal spores from the air.
Cooking Benefits
Koji unlocks richer flavor and texture in your favorite foods. This is made possible by the powerful enzymes koji produces, protease and amylase, which naturally amplify sweet and umami flavors by breaking down larger proteins and carbohydrates into savory amino acids and sweet sugars during fermentation. These powerful enzymes also naturally tenderizes whatever veggies or protein you're working with! Want to experiment with it in your own kitchen?
Learn to cook with koji
Health Benefits
Koji's powerful enzymes help predigest the nutrients in your favorite foods, boosting their availability and absorption. This process helps your body's digestion while supplying it with more available vitamins and minerals. Healthy and delicious? Count us in.
Koji also has prebiotic properties and is suspecting to be linked to the lengthened longevity in broader Japanese society.

How is koji made?

We carefully follow nine traditional steps to grow the best possible koji for all your projects.

Photography by Zach Phillips Creative

Step 1: Shinseki

Rice, our preferred substrate, must be soaked in fresh, cold water before beginning the next step →

Step 2: Mushi

The soaked rice is then steamed using a large steamer known as a koshiki.

Step 3: Hikikomi

The steamed rice is brought into the koji muro, where it's spread evenly across tables to cool to the ideal temperature for adding the koji spores.

Step 4: Tanekiri

The cooled rice is brought into the special koji growing room called the koji muro where the koji spores, or koji kin, are sprinkled over the cooked rice.

Step 5: Tokomomi

The koji inoculated rice is repeatedly kneaded to evenly distribute the koji spores. The rice is then mounded into a large pile and covered with a blanket to encourage spore growth.

Step 6: Kirikaeshi

After roughly 12-16 hours, the koji spores have create a dense mycellium (basically the "roots" of the mold) and the large pile must be broken up to release heat and moisture.

Step 7: Mori

To maintain stable temperature and moisture, the maturing rice koji is split into smaller trays.

Step 8: Shimai-shigoto

The rice koji located in the smaller trays must be continuously broken up and stirred to even distribute heat and moisture so that the koji does not overheat.

Step 9: Dekoji

The rice koji is now done. To finish, it is taken out of the koji muro to cool. All Koji House koji is frozen immediately after growth and dried to order to ensure maximum freshness and potency. Ready to start experimenting?

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More about koji

Koji: Frequently Asked Questions

What is koji made of?

Koji is always made using a species of mold from the genus Aspergillus, the most common of which are Aspergillus oryzae, Aspergillus sojae, Aspergillus niger, and Aspergillus awamori.

These molds can be grown on just about anything, but are happiest on cooked grains and legumes - these foods are referred to as the "substrate". Common substrates include rice, barley, and soy beans.

Is koji good for you?

Fermenting your food with koji helps increase the bioavailability of the food's essential vitamins and minerals.

Studies suggest that the glycosylceramide compounds found in koji act as prebiotics, specifically promoting the growth of beneficial bacteria like Blautia coccoides in the gut. That means tastier food for a healthier gut!

Does koji go bad?

Fresh koji has a shelf life of about 1 week, but can be frozen to increase the shelf life to several months.

Dried koji has a shelf life of several months to a year, granted it's stored in a dry and cool environment.

What foods is koji used to make?

Miso, soy sauce (shoyu) and sake are the most commonly known traditional foods, but dishes like amazake, sakadane, and shio koji also highlight the exceptional fermenting power of this amazing mold.

Japanese tradition is a good place to start, but koji can be used to enhance any cuisine! Throw it into a lactofermented hot sauce, sauerkraut, or kimchi for an added punch of umami.

Buy premium, hand-grown rice koji here:

Our koji is made fresh by koji masters at the North American Sake Brewery in Charlottesville, VA. Each small batch is crafted to give you maximum flavor and fermentation power in every recipe.

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