Row of thatched-roof huts at Myoban Yunosato, where the yunohana is made. (©Japan Forward/Mika Sugiura)
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About 15 minutes by car from Beppu Station, the hot spring village of Myoban Yunosato sits on a plateau around 350 meters (1,148 ft) above sea level. Thatched-roof huts dot the hillside, where wisps of steam and the scent of sulfur greet visitors as they arrive.
"Go ahead and place your hand on the ground," says Satomi Iikura. I do as she says and press my hand to the earth. A gentle warmth slowly spreads across my palm. "Hot spring steam fills the space about 30 centimeters (12 inches) below the surface," she explains.
A Hot Spring Legacy
Iikura's ancestor, Yoshisuke Wakiya, began producing Bungo Myoban—a form of alum—during the Edo period by crystallizing steam from the hot spring. Alum was a highly valued commodity used for dyeing fabrics, tanning leather, and as a styptic in medicine to stop bleeding. According to Iikura, at one time it was even procured exclusively by the Tokugawa shogunate.
When the Meiji era arrived, however, cheaper alum imported from China flooded the market, making the business unviable. Production shifted instead to yunohana, a byproduct of the alum-making process that can be used as bath salts.
The yunohana sold at hot spring resorts across Japan is usually a mineral deposit composed mainly of sulfur from hot spring water. Here, however, artisans channel geothermal steam into thatched huts made of bamboo and straw, where it reacts with blue clay to crystallize into yunohana. The crystals are said to grow by just one millimeter a day.
An Important Cultural Property
The huts are built in two layers: an inner lining of straw that absorbs moisture and an outer layer of reeds that repels it thanks to the reeds' natural oil content. "It's the wisdom of the old days," says Iikura.
The sulfur takes a toll on the structures, and craftsmen must re-thatch the huts every two years. Because of this distinctive production method and the striking landscape it creates, the site was designated an Important Intangible Folk Cultural Property of Japan in 2006.
According to Iikura, around 300 yunohana huts once stood on the site a century ago. Only 15 remain today. The 2016 Kumamoto earthquakes, which reached a seismic intensity of 7, damaged 11 of them, but all were restored over the following three years.
Inside the huts, temperatures rise to 30°C (86°F) even in winter and can reach 50°C in summer. Six craftsmen currently work at the site, which is sufficient for now, but training the next generation has become a pressing concern.
To keep the tradition alive and spark interest among younger people, the site hosts science workshops for elementary school students. The mineral-rich yunohana is also being incorporated into cosmetics, with plans to develop it into a recognized brand.
"We want to carry this 300-year-old industry forward into the future," says Iikura. "To do that, we first want people to understand what makes our yunohana truly special—and we hope to share that with the world."
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Author: Mika Sugiura
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