Racehorse Manure: The Secret Ingredient for Umami-Packed Button Mushrooms

Japan Forward

17-06-2025

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It wasn't until the 1960s that button mushrooms (also known as the cultivated mushroom or Agaricus bisporus ) became widely recognized in Japan.
In 1962, just two years before the first Tokyo Olympics, Japan was undergoing its "Income Doubling Plan," a national initiative aimed at achieving Western-level living standards and full employment. That year's hit song, "Itsudemo Yume Wo" ("Always Dreaming") by Yukio Hashi, captured the hopeful mood of the era, as people worked tirelessly toward a better future.
In October of the same year, four young men with unusual hairstyles and slim suits debuted in London with their song "Love Me Do." They were The Beatles. Their signature inward-curving bangs, later known as the "mushroom cut," quickly captivated young audiences around the world. Within two years, they had become global icons and symbols of cultural change.
Around this time, button mushrooms began to attract attention in Japan. But when the Tokyo Olympics arrived in 1964 and the country welcomed international guests, it became clear that Japan produced very little of one of the world's most commonly eaten mushrooms.
This realization prompted action. If button mushrooms were essential to Western dining tables, why not grow them in Japan too?
One of the first to take on the challenge was Yoshio Sugasawara, from what is now Katori City in Chiba Prefecture. Inspired by Dutch cultivation techniques, he began growing button mushrooms as a secondary crop alongside rice, laying the foundation for Japan's mushroom industry.
Sugasawara is the president of Yoshimoto Mushroom, a company founded in 1980. Out of the company's 88 production plants, 30 are located in Miho Village, Ibaraki Prefecture. Because of this concentration, Ibaraki ranks third in Japan for mushroom production value. Brown button mushroom pasta, served at a restaurant in Tokyo. (Courtesy of JA Ibaraki Prefecture Central Association)
The foundation for growing mushrooms is a medium called "bai-chi" (培地), which consists of two layers. The bottom layer is made from horse manure mixed with straw, known as "bakyuhi."
The Japan Racing Association's Miho Training Center houses over 2,000 racehorses. The manure produced there creates high-quality material essential for growing excellent mushrooms.
This manure is sterilized and cultured for over a month. Then, it's covered with peat moss, a natural organic soil conditioner, which helps the mushroom mycelium grow. When the dark peat moss becomes fully covered with white mycelium and mushrooms begin to sprout, the crop is ready for harvest. Trainer Toru Kurita walks alongside Titleholder, ridden by Kazuo Yokoyama at Miho Training Center in Ibaraki Prefecture on June 16, 2022. (©Sankei)
Japan's mushroom industry hasn't always had an easy path. Fresh mushrooms gained renewed attention during the 1970 Osaka Expo and benefited from the rising popularity of Western-style cuisine and family restaurants.
However, sales peaked in 1975. After that, the widespread use of combine harvesters for rice made it harder to gather the straw needed for mushroom cultivation. Between the 1980s and early 2000s, fresh mushrooms nearly disappeared from the Japanese market. Instead, canned salted mushrooms from China became common but were mostly used as decorative garnishes rather than tasty ingredients.
Despite these challenges, efforts to promote the rich flavor of fresh mushrooms have continued. They've appeared in salads, ajillo (garlic oil dishes), tempura, sake-steamed dishes, ramen, and even miso soup. Their savory umami taste has gradually won over more fans.
Still, average annual consumption in Japan remains just 32 grams per person — roughly two mushrooms. Yet button mushrooms hold great potential in Japanese cuisine, adding a boost of umami to everyday dishes.
Author: Shigeru Hagiya, Agricultural Policy Advisor, JA Ibaraki Prefecture Central Association
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