If Japanese food culture were pared down to just three fundamental elements, one might argue that it would be rice, fermentation and the four seasons. The one ingredient that embodies the three is kome kōji (rice that has been inoculated with kōji, the mold Aspergillus oryzae).

Koji Tanaka — his name is a coincidence — of Tanaka Farm in the Yokogoshi area of Niigata city makes kome kōji himself using rice he grows, a labor-intensive process that takes about four days.

First, the rice is washed and soaked in water overnight, after which it’s drained and steamed. The cooked rice is then laid out into shallow wooden boxes called kōji-buta to let excess moisture evaporate and cool the rice. Once the rice cools to below 40 degrees Celsius, kōji-kin (kōji spores, sometimes called kōji-tane, or kōji starter) is sprinkled on top and thoroughly incorporated into the rice.

Family fields: Koji Tanaka grows several strains of rice on his farm in Niigata Prefecture. | KOJI TANAKA
Family fields: Koji Tanaka grows several strains of rice on his farm in Niigata Prefecture. | KOJI TANAKA

The next day of the kōji-making process begins just after dawn when the kome kōji, just like a newborn, must be tended to every three hours. Tanaka once again crumbles the rice by hand so that the sticky, steamed grains gently detach from one another.

This process of te-ire (literally “putting your hand in”) helps keep the temperature of the kome kōji around 32 to 33 degrees Celsius, preventing the mold from damage and ensuring that the kōji-kin remains evenly incorporated into the rice. Finally, the kome kōji is confirmed for readiness by sight (when it’s white and firm) and smell (sweet).

Tanaka grows several rice varietals, all of which he makes into kome kōji. A former sake brewer, his motivation to start a farm on his ancestral family land began with the desire to make delicious food. As his family grew, so did his passion — his farm’s tagline is “making food for the family.”

“Kame no O fares better in kōji making than more modern varietals like Koshihikari as it has much less water content and more easily crumbles into single grains post-steaming,” he says.

Regardless of the strain of rice used to cultivate it, kome kōji can either be nama (freshly inoculated) or kansō (dried to remove moisture and lengthen shelf life), the latter of which can be found at most supermarkets.

However, Fumie Nakajima, a cook and instructor of Japanese plant-based cuisine, recommends making the effort to find fresh kōji as what she calls its “fermentation power” — how robust it is and how quickly fermentation occurs — is vastly different.

“Microbes determine whether lively fermentation can occur, she says. “Rice grown without the use of pesticides, herbicides or fertilizers allows kōji to ferment in this bright and peppy way,” says Nakajima.

Whether fresh or dried, it’s easy to adapt kome kōji for everyday recipes. Adding salt or soy sauce to kome kōji and allowing it to ferment at room temperature for several days makes for umami-packed all-purpose seasonings that can add flavor to salads, proteins, grains and even baked goods.

Fermented food products that also use kome kōji like miso, amazake (a sweet, drink made from fermented rice) and sanshō-zuke (a seasoning made of equal measures tōgarashi pepper, kome kōji and soy sauce) can be used in salad dressings, marinades, seasoning for rice and noodle dishes, or as kakushi-aji (a “secret ingredient”) in soups or stews.

Thanks to the enzymes in kome kōji, which break down food so it’s more easily digestible, and its efficacy in preserving food, it’s been a mainstay of the Japanese table for centuries. Kome kōji helps create the amino acids associated with umami: The soybeans in miso and the rice in sake and amazake are just a couple of the ingredients that release umami when incorporated with kome kōji.

These biological benefits, along with its emotional impact — it invokes memories of the smell of miso soup in the morning and the taste of shio-kōji- (salt kōji-) brined pickles — more than ensures kome kōji’s place in the Japanese kitchen for centuries to come.

Momoko Nakamura, aka Rice Girl, aims to promote and conserve rice culture and traditional Japanese natural farming. Her book, “Plant-based Tokyo,” is currently available in bookstores nationwide, as well as online.

Recipe: Shio Kōji


Kome kōji (rice that has been inoculated with kōji, the mold Aspergillus oryzae), either dried or, if you can find it, fresh

• Salt

• Water

• Soy sauce


To make shio kōji (a mix of kome kōji with salt), put a 1 to 1 to .35 ratio of plain kome kōji, water and salt in a jar.

Mix the ingredients, and store at room temperature away from sunlight. Stir the mixture once a day for about two to three weeks until it begins bubbling.

To make a shoyu kōji variant, repeat as above with a 1 to 1 ratio of soy sauce, and kome kōji instead of salt without water.

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