What Is Koji? And Why Are We Seeing It Everywhere? (2025)

You may not know koji by name, but it is a key ingredient for making traditional fermented Japanese products like soy sauce, miso and sake. Today, chefs around the world use koji to create umami-rich dishes. Consumer packaged goods companies are now starting to use it as as a flavor enhancer in plant-based meats, snacks and sauces.

What exactly is koji, and why are we seeing it everywhere? For more information, we consulted Kimberlie Le, co-founder of Prime Roots, a Berkeley-based producer of plant-based meats; Jun and Michael Sanders, co-owners of Spirit Almond, a gourmet Japanese-flavored almonds company based in Los Angeles; and chef Jeremy Umansky, co-owner of Larder Delicatessen & Bakery in Cleveland, co-author of Koji Alchemy: Rediscovering the Magic of Mold-Based Fermentation and co-founder of virtual conference Kojicon.

What Is Koji?

Koji is a type of mold called Aspergillus oryzae. Koji also refers to cooked rice (or other grains like barley) or soybeans that have been inoculated with that mold.

“As an enzyme, it [koji] breaks down starches into sugars and proteins into amino acids,” Michael explains. “The net effect of all that is enhanced aroma, flavor and umami.”

Umansky describes koji as a universal ingredient, something that can be used in any dish from any cuisine, sweet or savory. “Koji does have extreme cultural attachment, not just with the Japanese, the Koreans, the Filipinos, Indigenous Australians, Indigenous Russians that border the Pacific,” Umansky says. “The use of koji goes to Bangladesh and Pakistan, so there’s many cultural associations. It is that important that it’s a universal ingredient.”

What Is Koji Used For?

Koji is used as a fermentation starter to make Japanese products such as soy sauce, miso, sake and mirin. Koji-based condiments, including shoyu koji (made with soy sauce) and shio koji (made with salt), are also used in cooking to add umami and tenderize proteins. “Being Japanese, I grew up with Koji as an old and essential ingredient that’s used in all kinds of Japanese food,” Jun says. “Even after moving to the US, I’ve always used it in my home cooking. A quick marination with koji on beef, pork, chicken or fish before sauteing or grilling makes the proteins tender and incredibly flavorful.”

In the culinary world, chefs like Umansky and René Redzepi of Noma have discovered ways of harnessing koji’s fermentation powers.

Consumer product companies like Prime Roots and Spirit Almond are also tapping into its flavor potential.

“We are slowly taking advantage of what happens when koji eats something. And when it does that, it does incredible things to our food,” Umansky says. “It can potentially make our food healthier for us, easier to digest, more delicious, more flavorful, embolden the taste, change the texture in favorable ways—it can literally do all these different things.”

What Is Koji Meat?

Koji meat is a plant-based meat alternative that is made from koji. When looking for clean ingredients to make Prime Roots’ plant-based meats, Le discovered that koji naturally mimics the texture of meat and adds natural umami flavor. “Our koji grows in the same size and shape as meat muscle fibers and so it naturally produces a meat-like texture without having to resort to ultra-processing the protein,” Le says. “Our koji is also nutritious and full of protein and fiber.”

Prime Roots currently makes koji-based deli meats, charcuterie and bacon by cultivating and harvesting their own koji, mixing it with other plant- and fungi-derived products and adding seasoning. For the deli meats, casings are filled with the koji-meat, roasted, then chilled and sliced like regular deli meat. Le shares that koji naturally adds a deep umami flavor that enhances the nostalgic flavors and seasonings that inspire their products, like Hickory Koji-Bacon, infused with natural smoke flavor, or Black Forest Koji-Ham, seasoned with juniper, garlic and coriander.

How Does Koji Add Umami to Snack Foods?

For Spirit Almond’s Japanese-flavored almonds, Jun shares that koji brings out a deep, savory umami flavor without obscuring the natural sweetness and richness of California almonds. Spirit Almond makes two flavors utilizing koji, including their signature Koji Salt and Curry. (Technically the Miso flavor also incorporates koji.)

“In both cases, we use it as a seasoning—we roast the almonds with it, as opposed to using flavor powders on the almonds after they are roasted,” Michael says. “For our Curry flavor, with koji (and soy sauce), it takes on a distinctly Japanese curry flavor profile that it wouldn’t have with the other curry spices alone. The koji also gives it a smoothness, a richness. For Koji Salt, most of the flavor is coming from within the almond. There is a richness, a fullness that Koji unlocks like no other ingredient can.”

Shoyu koji and shio koji are also used to enhance umami in consumer packaged goods like sauces and pastes, including Omsom’s Yuzu Miso Glaze or Yokofuku’s Shio Koji Garlic Paste.

How Chefs Cook with Koji

At Larder Delicatessen & Bakery, Umansky, and co-owner and head baker Allie La Valle, incorporate koji into virtually every aspect of the menu, from breads to brines and charcuterie to cocktails. For charcuterie making, Umansky grows koji molds on the meats instead of other molds traditionally used to cure meats, like Penicillium, used to make dry salami or soppressata. “It’s more delicious, it works faster, and is all around better,” he says. For example, local brisket that is mixed with salt and koji and then dry-aged transforms the beef into a product that Umansky says rivals prosciutto.

On the baking side, koji is mixed with water and cooked at a specific temperature to charge up the enzymes. That liquid is then added to La Valle’s rye bread as the hydration; the extra enzymes aid the process of resting and relaxing of the dough, ultimately yielding a lighter texture. To put that in context, the average Jewish rye contains two to three percent rye flour; Larder’s has 20 percent. By utilizing liquid extract of koji, Umansky says, the rye loaf achieves a light and fluffy texture instead of one that is dense and heavy.

To enhance chocolate flavors in Larder’s pastry program, La Valle utilizes douchi, fermented and salted beans that are used to make things like Japanese soy sauce and miso or Chinese black bean sauces. At Larder, chickpeas are inoculated with koji, heavily salted and dried. The beans are then crushed and sprinkled onto brownies, baked into cookies or anywhere chocolate needs enhancement. “If you were able to make a bouillon or instant mole sauce, that’s what this little dried bean smells like when it’s crushed up,” Umansky says. “You get sweet spices, it smells like dried fruit, it smells like chocolate—and all of this from a salt cured bean that we grew some mold on.”

Koji is also used in Larder’s beverages. For a whole lemon lemonade, lemons, sugar and koji are tightly sealed in jar, left to sit and then the whole mixture is blended and mixed with seltzer. “There’s no waste, we don’t have extra pith and peel and seeds,” Umansky says. “The more of our food we keep in our food the more delicious it will be.” Larder’s Koji Sour, a riff on a whiskey sour, features koji two ways, including amazake, a non-salted liquid extract of koji that is used to make a mildly sweet fermented rice beverage in Japan, and koji syrup, made by growing koji on overcooked rice. Because the rice is overcooked, Umansky explains, the mold can only grow on the surface of the rice; the root network grows like a net and creates a lot of sugar from the starch in the overcooked rice. As it grows, it pulls and tightens the rice and squeezes out the sugary liquid.

How to Cook with Koji at Home

For koji-curious home cooks, Umansky recommends starting with baking. Take your favorite chocolate chip cookie recipe and replace the salt with equal parts miso; perhaps a younger miso (white or yellow) for milk chocolate chip cookies, or a darker, aged miso (like red) with a dark chocolate chip cookie. For recipe inspo, try our fan-favorite Chocolate Chip Cookies or Katie Lee Biegel’s Secret Ingredient (Miso!) Chocolate Chip Cookies.

Related Links:

36 Delicious Japanese Recipes

36 Delicious (And Sometimes Surprising!) Ways to Use Miso Paste

Our Best Plant-Based Recipes