Koji is a strain of *Aspergillus oryzae*, a fungus used for various culinary purposes, including the production of alcoholic beverages like [sake](https://www.masterclass.com/articles/sake-guide) or shōchū, or invaluable condiments like miso, [mirin](https://www.masterclass.com/articles/how-to-cook-with-japanese-sweet-rice-wine), and shōyu (soy sauce). 

Like [yeast starters](https://www.masterclass.com/articles/fresh-yeast-explained) in bread making, koji kickstarts the fermentation process when added to other base ingredients, like soybeans, rice, or wheat grains like [barley](https://www.masterclass.com/articles/how-to-cook-barley-at-home). When applied to proteins, koji acts as a curing agent in the production of charcuterie. The enzymes present in koji molds (like amylase and glutamate) transform starches and proteins into amino acids and sugars. The resulting flavors define the realm of [umami](https://www.masterclass.com/articles/what-is-umami-learn-about-umami-and-how-to-incorporate-umami-flavors-in-your-cooking): sweet, savory, salty, with an undertone of pleasing funk. 

Koji can also refer to other molds in the same bacterial family; for example, *Aspergillus sojae*, rather than *Aspergillus oryzae,* may also be used to make [miso](https://www.masterclass.com/articles/what-is-miso-easy-miso-broth-recipe-with-chef-gordon-ramsay) and shōyu.
Koji rice—steamed rice inoculated with koji mold and allowed to ferment for just over two days—acts as a starter for many fermented foods in traditional Japanese cuisine. In addition to rice, koji is also commonly used on barley grains and [sweet potato](https://www.masterclass.com/articles/japanese-sweet-potato-recipe) and can be purchased at most Asian grocery stores.

1. __Alcoholic beverages__: Various koji strains (like white, yellow, and black koji) are used to impart distinct flavors while serving as the fermenting agent in brewed sake, distilled *shōchū*, and Okinawa-style *awamori*. It’s also the main ingredient in *amazake*, a naturally sweet beverage with a low alcohol content that can also be eaten as a porridge-esque dessert. 
2. __Cooking condiments__: Rice vinegar and mirin, a sweet cooking wine, both result from the enzyme activity of koji. Mirin combines koji with short-grain *mochigome* sweet rice and *shōchū*, while [rice vinegar](https://www.masterclass.com/articles/what-is-rice-vinegar-how-to-cook-with-rice-vinegar-and-best-rice-vinegar-substitutes) adds yeast to the converted sugars in koji rice, followed by acetic acid. 
3. __Miso__: Miso paste is the result of combining koji molds with cooked soybeans, salt, and water and allowing it to develop both its signature pasty texture and umami flavor. You can use miso paste as a condiment, a pickling agent, and a base for marinades and dishes like [miso soup](https://www.masterclass.com/articles/authentic-japanese-miso-soup-recipe) or *nasu dengaku*, miso-glazed eggplant.
4. __*Shio* koji__: Koji rice is combined with salt and water and left to ferment for a few weeks at room temperature to make koji salt. The result is a crumbly, flavor-packed paste that can be used as a salt substitute in everything from stir-fries to marinades. Learn how to make [stir-fry](https://www.masterclass.com/articles/how-to-make-a-perfect-stir-fry) for your next weeknight meal. 
5. __Shōyu (soy sauce)__: This Japanese-style [soy sauce](https://www.masterclass.com/articles/soy-sauce-explained) is made using the same technique as [miso paste](https://www.masterclass.com/articles/types-of-miso-paste)—applying koji molds to a soybean and salt mash and allowing fermentation to occur—except the mixture is pressed and filtered to create a liquid byproduct.
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Hailed as Japan’s “national fungus,” koji mold plays a foundational role in much of the country’s traditional cuisine.

Hailed as Japan’s “national fungus,” koji mold plays a foundational role in much of the country’s traditional cuisine.

What Is Koji? 5 Common Koji Uses

Koji is a strain of Aspergillus oryzae, a fungus used for various culinary purposes, including the production of alcoholic beverages like <a href='https://www.masterclass.com/articles/sake-guide' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/sake-guide","linkCopy":"sake","category":null}'>sake</a> or shōchū, or invaluable condiments like miso, <a href='https://www.masterclass.com/articles/how-to-cook-with-japanese-sweet-rice-wine' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/how-to-cook-with-japanese-sweet-rice-wine","linkCopy":"mirin","category":null}'>mirin</a>, and shōyu (soy sauce). Like <a href='https://www.masterclass.com/articles/fresh-yeast-explained' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/fresh-yeast-explained","linkCopy":"yeast starters","category":null}'>yeast starters</a> in bread making, koji kickstarts the fermentation process when added to other base ingredients, like soybeans, rice, or wheat grains like <a href='https://www.masterclass.com/articles/how-to-cook-barley-at-home' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/how-to-cook-barley-at-home","linkCopy":"barley","category":null}'>barley</a>. When applied to proteins, koji acts as a curing agent in the production of charcuterie. The enzymes present in koji molds (like amylase and glutamate) transform starches and proteins into amino acids and sugars. The resulting flavors define the realm of <a href='https://www.masterclass.com/articles/what-is-umami-learn-about-umami-and-how-to-incorporate-umami-flavors-in-your-cooking' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/what-is-umami-learn-about-umami-and-how-to-incorporate-umami-flavors-in-your-cooking","linkCopy":"umami","category":null}'>umami</a>: sweet, savory, salty, with an undertone of pleasing funk. Koji can also refer to other molds in the same bacterial family; for example, Aspergillus sojae, rather than Aspergillus oryzae, may also be used to make <a href='https://www.masterclass.com/articles/what-is-miso-easy-miso-broth-recipe-with-chef-gordon-ramsay' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/what-is-miso-easy-miso-broth-recipe-with-chef-gordon-ramsay","linkCopy":"miso","category":null}'>miso</a> and shōyu.

What Is Koji?

Koji rice—steamed rice inoculated with koji mold and allowed to ferment for just over two days—acts as a starter for many fermented foods in traditional Japanese cuisine. In addition to rice, koji is also commonly used on barley grains and <a href='https://www.masterclass.com/articles/japanese-sweet-potato-recipe' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/japanese-sweet-potato-recipe","linkCopy":"sweet potato","category":null}'>sweet potato</a> and can be purchased at most Asian grocery stores.<ol class="mc-m-4"><li class="mc-my-4"> 1. Alcoholic beverages: Various koji strains (like white, yellow, and black koji) are used to impart distinct flavors while serving as the fermenting agent in brewed sake, distilled shōchū, and Okinawa-style awamori. It’s also the main ingredient in amazake, a naturally sweet beverage with a low alcohol content that can also be eaten as a porridge-esque dessert. </li><li class="mc-my-4"> 2. Cooking condiments: Rice vinegar and mirin, a sweet cooking wine, both result from the enzyme activity of koji. Mirin combines koji with short-grain mochigome sweet rice and shōchū, while <a href='https://www.masterclass.com/articles/what-is-rice-vinegar-how-to-cook-with-rice-vinegar-and-best-rice-vinegar-substitutes' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/what-is-rice-vinegar-how-to-cook-with-rice-vinegar-and-best-rice-vinegar-substitutes","linkCopy":"rice vinegar","category":null}'>rice vinegar</a> adds yeast to the converted sugars in koji rice, followed by acetic acid. </li><li class="mc-my-4"> 3. Miso: Miso paste is the result of combining koji molds with cooked soybeans, salt, and water and allowing it to develop both its signature pasty texture and umami flavor. You can use miso paste as a condiment, a pickling agent, and a base for marinades and dishes like <a href='https://www.masterclass.com/articles/authentic-japanese-miso-soup-recipe' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/authentic-japanese-miso-soup-recipe","linkCopy":"miso soup","category":null}'>miso soup</a> or nasu dengaku, miso-glazed eggplant. </li><li class="mc-my-4"> 4. Shio koji: Koji rice is combined with salt and water and left to ferment for a few weeks at room temperature to make koji salt. The result is a crumbly, flavor-packed paste that can be used as a salt substitute in everything from stir-fries to marinades. Learn how to make <a href='https://www.masterclass.com/articles/how-to-make-a-perfect-stir-fry' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/how-to-make-a-perfect-stir-fry","linkCopy":"stir-fry","category":null}'>stir-fry</a> for your next weeknight meal. </li><li class="mc-my-4"> 5. Shōyu (soy sauce): This Japanese-style <a href='https://www.masterclass.com/articles/soy-sauce-explained' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/soy-sauce-explained","linkCopy":"soy sauce","category":null}'>soy sauce</a> is made using the same technique as <a href='https://www.masterclass.com/articles/types-of-miso-paste' target='_self' class='mc-text--link' data-mc-segment-trigger='true' data-mc-segment-event-type='Article Page Click' data-event-obj='{"textTag":"p","href":"https://www.masterclass.com/articles/types-of-miso-paste","linkCopy":"miso paste","category":null}'>miso paste</a>—applying koji molds to a soybean and salt mash and allowing fermentation to occur—except the mixture is pressed and filtered to create a liquid byproduct. </li></ol>

5 Common Koji Uses

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Hailed as Japan’s “national fungus,” koji mold plays a foundational role in much of the country’s traditional cuisine.

Hailed as Japan’s “national fungus,” koji mold plays a foundational role in much of the country’s traditional cuisine.
