Kinkatsu Day

What Is Kinkatsu Day?

Every May 24th is "Kinkatsu Day" (菌活の日, Kinkatsu no Hi) in Japan. "Kinkatsu" (菌活) — literally "fungi/microbe activity" — means actively incorporating fungi and other beneficial microbes into your diet throughout the year. The term was popularized by Hokuto Corporation (ホクト株式会社), a mushroom company headquartered in Nagano City, which established the day. The date marks May 24, 2013, when the company first broadcast the word "kinkatsu" nationwide in a TV commercial. The company highlights mushrooms as a food in which you eat the fungi themselves.

Fermentation in Japanese Food Culture

Japan has a rich fermentation tradition, with many fermented foods integrated into everyday cuisine. Core fermented products include miso (味噌, fermented soybean paste), soy sauce (醤油, shōyu), sake (日本酒), mirin (みりん, sweet rice seasoning), rice vinegar (酢), natto (納豆, fermented soybeans), tsukemono (漬け物, pickles), and katsuobushi (鰹節, dried skipjack tuna, some types of which are cured with mold). Each involves microbial activity — bacteria, yeasts, and molds — that transforms raw ingredients into foods with deep flavor.

Koji: The Heart of Japanese Fermentation

At the center of Japan's fermentation tradition is koji (麹) — made with the mold Aspergillus oryzae, which grows on steamed rice or soybeans and produces enzymes that break down starches and proteins. Koji is the starting point for sake, miso, soy sauce, mirin, and many other fermented products. In 2006, the Brewing Society of Japan named Aspergillus oryzae Japan's "national fungus" (国菌, kokkin).

Mushrooms and Microbes

While fermented foods are made through the work of microbes, mushrooms are fungi themselves. Though sold alongside vegetables, mushrooms are not plants; the part we eat is the fruiting body, which produces spores. Beneficial live microbes are known as "probiotics," while dietary fiber and oligosaccharides that feed gut bacteria are called "prebiotics." The makeup of gut bacteria is known to vary greatly from person to person.

Fun Facts

• Metchnikoff and yogurt: Nobel laureate Élie Metchnikoff is known for drawing attention, in the early 20th century, to Bulgarian yogurt and longevity — which helped popularize yogurt around the world.
• Natto's acquired taste: Natto (納豆) — fermented soybeans with a sticky, stringy texture and pungent aroma — is a classic breakfast food in Japan, but remains an "acquired taste" for many people encountering it for the first time.