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Meet the famous Japanese mold that flavors unexpected dishes

Cari Spivak


On Saturdays, Mariko Grady’s company, Aedan Fermented Foods, has a food stall at the San Francisco Ferry Plaza Farmers Market.

They sell a handful of Japanese fermented staples, including their 2018 Good Food award winning Country Miso, a fermented paste made from soybeans, salt, rice, barley and the Japanese mold called koji. Mariko has become something of a koji ambassador at the Ferry Plaza, explaining koji to anyone who walks by.


“Koji has many enzymes,” she starts off, then holds up a mason jar. Inside is a block of white rice which, up close, looks like it’s covered in frost. This is rice koji. It’s cooked rice that’s fermented for three days with Aspergillus oryzae. This mold is necessary to make Mariko’s Country Miso, as well as other Japanese staples such as soy sauce, rice vinegar, and sake.

Without koji, Mariko says, there wouldn’t be Japanese food. And now, chefs in the Bay Area are using Mariko’s koji to develop the flavors in other types of food.

Chris Porter is a cook at Californios, a Michelin-star restaurant. His boss, David Yoshimura, is chef de cuisine, and he brought Chris to the farmer’s market meet Mariko. Chris uses Mariko’s products every day at the Mexican-inspired Californios.

He was asking David about koji and how to make miso. “So I was like, ‘you should just ask Mariko’,” he says.

“I would love to be able to make miso from other grains that aren’t necessarily used in Japanese cooking,” Chris explains. “Like maybe black-eyed pea miso or heirloom beans miso.”

These days, if you eat at a good restaurant, it’s possible you’re eating something made with koji, even if it’s not Japanese food.

In the Bay Area, Mariko supplies well-known restaurants like Manresa, Lazy Bear, Jardiniere, and Madera with ricekoji products. Californios uses Mariko’s shio koji shio koji is a simple but powerful marinade made from rice koji, salt and water — to make a Mexican-style ceviche.  

Chris says, “It adds a nice depth of flavor without really adding any extra ingredients. So it’s kind of a nice surprise when people bite into it that it has that extra flavor that they might not expect.”

That unexpected flavor is umami.

Literally translated from Japanese, umami means “deliciousness.” There are five tastes: salty, sweet, sour, bitter, and umami.


Foods with strong umami are high in amino acids. You get amino acids by breaking down proteins. It’s like what happens when you age meat: the enzymes break down the protein and you wind up with tastier steak.

The enzymes inkoji do the same thing to other foods. Plus it’s versatile: a short marinade in shio koji can give almost anything an umami boost.

Koji has been around for thousands of years. It’s so essential in Japan that, starting in 2004, it starred as a character in an award-winning Japanese manga, or graphic novel, called “Moyashimon,” that ran for ten years and spun off into an anime and a live-action TV show.

During that time, the Association for Japanese Brewers named koji a “national treasure.”

It’s celebrated on National Fungus Day.

But Mariko Grady didn’t get started in the koji business because of koji’s popstar status. Fifteen years ago she was a professional dancer and singer with the Pappa Tarahumara performing arts company.

When she wasn’t on tour internationally, she was rehearsing in Tokyo, or living in San Francisco with her husband and daughter.

As a hobby, she made her own miso from pre-packaged rice koji that she purchased in Japan.

But then, in 2011, a 9.1 magnitude earthquake struck near the east coast of Japan. It caused a tsunami which started a nuclear disaster at the Fukushima Daiichi nuclear plant.

Mariko was in San Francisco at the time and remembers how worried she was for friends who lived in Tokyo and Fukushima. It took a long time until people understood the threat of radiation exposure.

In San Francisco, the Japanese community at Mariko’s daughter’s elementary school started a fundraiser for victims of the disaster. Mariko wanted to make something to contribute, so she sold her homemade miso.

But her friends bought all of her miso and she quickly sold out. In the process, Mariko used up all the prepared rice koji she had bought in Japan.

And because of the earthquake, she couldn't return to Japan to buy more.

In the back of her kitchen cabinet, she noticed a package of green powder. It was the the koji mold, Aspergillus oryzae. So she used it to make her own rice koji.

And a business was born.

Today she makes 150 pounds of rice koji a week at the La Cucina communal kitchen in the Mission.

I visited her there one Sunday morning, and she showed me a wooden box like the ones used to store wine bottles. Inside was rice koji, wrapped in a towel. It had been 72 hours since she innocculated the rice with the mold, and it smelled fruity.

“Fresh rice koji,” she says, proudly. She held it up for me touch. It was warm. “They are alive,” she explains. “It’s like a baby; it’s life.”

This rice koji will be the starter for four different kinds of miso, shio koji, amazake, a sweet rice drink, and sagohachi, a pickling sauce. Her koji products are made with locally grown organic Koda Farms rice. You can buy koji products, especially shio koji, on the internet or at Asian markets; but Mariko says that in the Bay Area her shio koji is the only one that is organic and sold fresh.

Running her company means Mariko no longer performs professionally, but she says she finds a way to connect with a different audience.

“Koji listen or feel my good energy through my voice or through my hand,” she says. “So always, I want to keep good energy like [a] performer.”

You can find Aedan Fermented foods at local farmers markets and grocery stores in the Bay Area. Check out the Aedan Fermented foods website to taste food made with koji.


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