Modern Chefs Are Finding New, Nutritious Flavors With the Help of an Ancient Fungus

Soy sauce is no longer considered an exotic Asian ingredient but a pantry staple that’s found on the shelves of supermarkets and convenience stores across America. Miso—one of the world’s great building blocks of flavor—has an ever-increasing following, too, especially because it gives richness and a boost of protein to all manner of vegetarian and vegan dishes.

Both are among the various fermented seasonings, foods, and beverages that make the Japanese diet so distinctive, delicious, and healthful. What many of them—including not just soy sauce and miso but mirin, rice vinegar, sake, and shochu—have in common is the fermenting agent koji, a filamentous (stringlike) fungus in the Aspergillus genus. The most common microorganism in koji production is A. oryzae, but others include A. sojae, A. usami, A. awamori, and A. kawachii.

Koji is so integral to Japanese food and drink that it’s regarded as part of the cultural heritage; the Brewing Society of Japan declared it a national fungus in 2006. It’s also used in China and Korea (where it is known as qu and nurukgyun, respectively) to ferment foods.

The term koji, by the way, refers not just to the fungus but to an ingredient that’s typically made with rice, barley, or soybeans. According to the Tokyo Foundation, tane koji (“seed koji”) are the spores of A. oryzae, and actual koji is “made by sprinkling tane koji over steamed rice, barley, or soybeans and cultivating the fungus under temperate conditions suitable for its growth. As the fungus propagates, enzymes break down the grains’ starch and proteins into sugars and amino acids…. Koji can take on a variety of characteristics depending on what kind of seed koji and grains are used to make them.”

Thanks to the Tokyo Foundation, here’s a fun fact for your next visit to a sake bar: The koji for brewing premium sake and that for brewing regular sake are made with distinct types of seed koji, as well as distinct types of rice. Highly polished rice is used for the former and less polished rice for the latter. You’re welcome! I’m here to serve.

As long as you indulge my historical diversions, that is. You may also be interested to learn, for instance, that in the brewing industry seed koji are distributed by only a dozen or so seed koji dealers, descendants of the jinnin who served in shrines centuries ago. In the Muromachi era (1336–1573), the shogunate exempted jinnin from a tax that was usually levied on those making koji. Naturally, they soon formed a union and monopolized the production and sale of koji in the old imperial capital of Kyoto.

DIY fermenters will find more details regarding koji-making processes at Nordic Food Lab, which uses diverse substrates, including pearled barley (the Food Lab’s mainstay), heritage barley varieties such as nøgen byg, buckwheat, rye, quinoa, sunflower seeds, various beans, and more.

At this point, you probably are thinking that chefs are all over koji like white on rice, and you’d be right. At Locol, in the South Los Angeles neighborhood of Watts, for example, cofounders and chefs Roy Choi and Daniel Patterson are serving a fabulous beef-grain-tofu Burg on a koji-leavened whole-grain bun, which manages to combine the soft, yielding come-hither texture of white bread with nutritional density. A win-win, in other words.

Also in Los Angeles, in a strip mall near Hollywood Forever Cemetery (just typing those words is such fun), you’ll find Baroo, where chef Kwang Uh mixes roasted koji beet cream with grains like farro, Kamut, and Job’s tears in his signature dish noorook. Joshua Lurie of Food GPS writes about Uh and his extraordinary “restaurant-cum-experiment” in the inaugural issue of Cured, a magazine devoted to the many brilliant, inventive methods we humans have developed over millennia to make foods last. (Full disclosure: I’m the executive editor, and yes, I know, at 20 bucks, it’s expensive. But it’s not only gorgeous but packed with great stuff—a keeper.)

As it happens, koji is a gift that keeps on giving. “One of the prominent potentials of A. oryzae is that it has been successfully applied to effective degradation of biodegradable plastic,” wrote Masayuki Machida, Osamu Yamada, and Katsuya Gomi for the Oxford journal DNA Research. “Genomic analysis in concert with traditional knowledge and technology will continue to be powerful tools in the future exploration of A. oryzae.” Somewhere, the jinnin are smiling.