Shio Koji (Fermented Rice Koji and Salt)

shio koji in spoon
© Judy Ung

Shio koji is an ingredient in Japanese cooking with a history of at least a few hundred years. In Japanese, shio means salt. Koji (also known as koji-kin) is a fungus or mold used to ferment foods or make alcoholic beverages. The term koji can also refer to the fermented food itself, for example, the end product that is created when the mold and grain (rice, soybean, etc.) are broken down. 

What Is Koji?

The koji used in Japanese food refers to the fungus Aspergillus oryzae (A. oryzae), a mold that is thought to have existed at least 2,000 years ago. This mold is used to produce miso (soybean paste), sake (alcohol for cooking and drinking), mirin (sweet cooking sake or alcohol), rice vinegar, soy sauce, as well as alcoholic beverages. This mold is used similarly in Chinese and Korean cuisine to ferment food and drinks.

What Is Shio Koji?

Shio koji is a mixture of fermented sea salt and short-grain white rice. When Aspergillus oryzae is combined with salt and steamed rice, then left in a warm environment to age, the rice grains break down into enzymes, glutamates, and sugars, imparting a mild salty taste with big umami (the so-called fifth human taste) flavors. Shio koji has the appearance of a thick and lumpy white paste and looks similar to rice gruel.

How to Use Shio Koji

Shio koji is a versatile ingredient and can be used in many ways. For example, to tenderize and season meats and fish is most popular, to pickle vegetables, or make homemade salad dressings. Other ways in which shio koji might be used as a substitute for soy sauce or salt in any recipe such as stir-fry, simmered dishes, baked goods, or even meatballs. A general rule of thumb is substituting about two teaspoons of shio koji for every one teaspoon of salt. The possible applications for shio koji are endless, and not just limited to Japanese cuisine.

Some health advocates of shio koji laud the many benefits of this ingredient to the human body due to its natural properties. While there are some who believe these purported benefits, others merely enjoy shio koji as a lower-sodium alternative to salt or soy sauce, and for its umami infusing capabilities.

Where to Buy Shio Koji

Shio koji is available for purchase in Japan and some Japanese and Asian supermarkets in the West. Shio koji may also be purchased via online food retailers. Ready-for-use shio koji products sold at grocery stores are typically found in the refrigerated section and often include a small amount of alcohol as a preservative.

It is also possible to make shio koji at home using kome-koji (a mixture of fermented A. oryzae and steamed rice) and salt, but it has a shorter shelf life than that which is sold in the supermarket.