Where does shio koji come from, and how is it used?

Shio koji is a unique ingredient that imparts a subtle yet powerful flavor to many Japanese products. Both condiment and seasoning, shio koji is a paste made from a base of koji spores, a mold known scientifically as Aspergillus oryzae. The spore is cultured on cooked rice to create a raw ingredient that adds magic to Japanese dishes.

While koji is prevalent in modern dishes, the ingredient has been used in Japanese cuisine for thousands of years. Although it’s difficult to pinpoint precisely how koji was discovered, many experts believe it may have been unearthed during the Yayoi era in line with the development of rice farming. However, one of the first recorded uses comes from a text written during the Nara era in the early 8th century. 

Shio koji has many uses in the kitchen. It can be added in dry form as a cultured grain, or liquidized and often combined with other aromatics. Japanese chefs use this unique ingredient to marinade fish and meat, as a base for pickling vegetables, to enrich dressings, and as an all-purpose seasoning for any dish that benefits from a savory hit. 

How is shio koji produced today?

Although koji production has gone industrial, like many traditional practices regarding artisan products in Japan, the soul of the process has changed little in its 2,000-year history. The first step in making koji paste is growing the koji.

For this process, Aspergillus culture is often added to steamed rice or soya beans. Next, the combined ingredients are left in a humid environment for several days on wooden trays to ferment. During this time, the mold eats away at the fuel, breaking down sugars and carbohydrates. 

An essential ingredient in soy sauce, mirin and sake

Soy sauce, mirin and sake use koji as an essential element in brewing and fermentation. The koji imparts a robust, savory flavor to the liquids, a taste heralded in Japan, and an iconic umami bite that you can’t replicate with other ingredients. 

When koji breaks down carbohydrates and proteins, they turn them into amino and fatty acids and simple sugars. The most important of these reactions is the release of glutamate; this is the umami powerhouse that imparts so much depth to these iconic sauces and beverages. 

Good mold vs. bad mold: What’s the difference?

Unsurprisingly, mold has got a bad rap. Why? Because while some molds can impart inexplicable depth to cured meats, cheeses and fermented sauces, others can be harmful, or even toxic.

A mold is a type of fungus, and as with any fungus, identification is critical. While shio koji is a safe fungus, others, like mildew, commonly occurring in damp areas of the home, can cause headaches, nausea, coughing and other mild symptoms. However, some more toxic molds can even be deadly. The most important thing is relying on experts to pick and choose from the right molds to use when creating exciting flavors.