Koji Day

What Is Koji Day?

August 8th is "Koji Day" in Japan, honoring koji, the fermentation starter essential to Japanese cuisine. The kanji for koji (麹) contains the character for "rice" (米), which itself breaks down into "eighty-eight" (八十八) -- the basis for the date. It was established by Hanamaruki Co., based in Ina, Nagano Prefecture.

Koji, the Unsung Hero Behind Miso and Soy Sauce

Koji is made by cultivating koji mold on steamed rice or soybeans, and it's indispensable to Japan's fermented food traditions.

• Origin: traces to the structure of the kanji itself -- the "rice" character inside "koji" breaks down into "eighty-eight"
• Purpose: to spread wider appreciation for koji-based fermented foods, from miso and soy sauce to sake and mirin
• Koji as Japan's "national fungus": officially designated the "national fungus" by the Brewing Society of Japan, symbolizing its role in Japanese food culture

An All-Purpose Seasoning Rediscovered Through the "Shio-Koji" Boom

Koji used directly as a seasoning -- in the form of shio-koji (salted koji) or shoyu-koji (soy sauce koji) -- has drawn major attention amid the recent fermentation boom, and is now widely used in home cooking.

Tips for Marking This Day

• Cook with koji-based seasonings like miso or soy sauce, mindfully today
• Try making a koji-based food, like shio-koji or amazake
• Learn about how koji fermentation actually works
• Look for regional dishes or fermented foods that use koji

An Invisible Microscopic Mold Supports All of Japanese Cuisine

Without the work of koji mold, sometimes called Japan's "national fungus," there would be no miso, no soy sauce, no sake. August 8th is a day to give thanks to koji, the quiet force behind Japan's food culture.