Japanese fermented foods: Koji

Written by Kevin Kilcoyne (@kevinjkilcoyne)

With countless varieties of condiments, dishes, and pickles (known generally astsukemono), Japan has an incredibly rich culinary history of fermented products. To name a few there aremiso, shoyu (soy sauce),natto, umeboshi (pickled plum),umeshu (plum liqueur),sake, andkatsuo-bushi (dried, fermented bonito fish.) All are the products of centuries of experimentation and perfection in an environment rich in fermentation-friendly microbes and a climate that suits them perfectly.

As diverse as Japanese fermented foods might be, one microbe stands above the rest and that is the moldkoji.

Also known asAspergillus oryzae, koji is responsible for many of the ingredients that make up the foundation of Japanese cuisine. Professor, researcher, and authorMakoto Kanauchi says that products likemiso, mirin, shoyu,and sake, would not exist if it weren’t for the symbiosis betweenkoji and the fermentation-conducive enviornment of Japan. Furthermore, he says thatkoji is so beloved by the Japanese people that it has been called the Japanese national fungi and is even celebrated yearly on October the 12th, National Fungus Day.

When speaking ofkoji, the term kojiis used when referring to both the microbe itself as well as thekoji-cultured grains used in fermentation. Grains like rice, barley, and soy beans are inoculated with thekoji mold and then fermented to create thekoji culture. They are then used to create the fermented products likeshoyu, miso,andsake. In Japanese, however, the mold and the culture can be differentiated even further. The mold spores themselves are calledkoji-kin(麹菌) and although various grains can be used to create a mother culture, the most common is steamed rice, which once inoculated, becomeskome-koji (米麹/米粉) or ricekoji.

Kome-kojiis a key ingredient in the production ofmirin, sake,andmiso.It is also the key ingredient in another traditional staple of Japanese cuisine calledshio koji, or saltkoji. Likeshoyu andmiso,shio koji is used to season dishes, whether as a marinade or a substitute for salt, and can be used to cure and preserve foods as well.

The difference withshio koji, however, is both in the way in which it is produced and the way it flavors the ingredients it is combined with.Shio koji is simply amixture ofkome koji, salt, and water. The mixture is then left to ferment. As it ages, it develops flavor as the microbes do their work, turning something that was once dominantly salty into something mildly salty with a faint sweetness.

As with many fermented foods, the products produced usingkoji are often more nutritious than the original un-fermented ingredients. Shio koji is no different. When rice is introduced tokoji-kin and allowed to culture, it releases hundreds of enzymes and compounds within the rice that would otherwise be inaccessible or less bioavailable. In a way, the fermentation process acts as a pre-digestion stage, making foods more easily digestible and nutritive. This attribute extends toshio kojias well,which when used as a marinade, helps to break down proteins and tenderize meat and fish, bringing out theumamiin the ingredients, while also breaking down starches to draw out their sweetness.

Rich in probiotics, ingredients likemiso andshio-koji also help to keep our digestion systems healthy and our gut microbiomes in check. So perhaps in your next recipe, substitute some salt forshio koji and some sugar foramazake, for a healthy boost in your gut flora. You might just find a depth of flavor you had not experienced with the same ingredients before.

About the author: The spark that lit Kevin Kilcoyne’s interest in Japanese culture began in elementary school through a friendship with his then classmate Keisuke. Since then, that passion has evolved and bloomed to encompass more than just video games and manga, leading Kevin to live in Japan as a participant of the JET program. During his time in Japan, Kevin sought out as many foods as he could, the experiences and taste memories lingering long after they had gone. Now he is forging a path to link his passions for Japanese food, history, and visual culture and is planning for his return to live in Japan once again. For now, you can find Kevin on Instagram (@kevinjkilcoyne) where he posts his illustration work. Keep an eye out for more posts and updates as Kevin delves more deeply into his passions for writing and food.