KAWAGUCHI, Saitama >> Brewer Yuji Shimada carefully holds the stem of a short wine glass and pours a clear, golden liquid from one of the taps mounted on the commercial refrigerator, the light fizz from natural carbonation creating a thin layer of foam reminiscent of beer head.

“This is what we call the ‘original’ with no additional flavoring, just the basic ingredients: green tea, black tea, sugar and the fungus for fermentation,” the bespectacled 42-year-old said.

“We’re the only brewery in Japan with a license to produce nonheated kombucha.”

Here at Oizumi Kojo, a company located in the industrial quarters of Kawaguchi, a city in Tokyo’s neighboring Saitama Prefecture, Shimada and his assistant are running the nation’s first commercial- scale brewery producing kegs of unpasteurized “raw” kombucha, the tea-based beverage that’s become a multimillion-dollar industry in the U.S., where its purported health benefits have made it a favorite among millennials, models and athletes.

It was once a big thing in Japan, too, about four decades ago and under a different moniker. Back then it was called kocha kinoko (mushroom tea), a name derived from how the “scoby” — short for the “symbiotic culture of bacteria and yeast,” an ingredient used in the fermentation process — resembles a mushroom.

There are various theories regarding the origins of the drink, some dating it back to 200 B.C. in Manchuria. It is thought to have eventually made its way to Russia, where lore has it that inhabitants of a Siberian village were living to a ripe old age thanks to the beverage made from the mysterious fungi.

It became a sensation in Japan when a book hailing its health benefits was published in 1974 by a widow in her 70s who said she received a piece of the jelly-like fungus from a Japanese who brought it back from the Siberian village. The book came with a mail-order coupon that offered a slice of the fungus, and soon households began making their own probiotic drinks in glass jars, claiming it could prevent ailments ranging from constipation to cancer. But the boom soon died out after medical experts began to question its benefits.

The funky tea then made its way to South Korea, and finally to the U.S., where it was commercialized in the mid-1990s.

Now Japan seems to be cautiously catching on to the trend it once embraced so fervently. But the concoction’s new alias may be a marketing obstacle: In Japanese, kombucha typically refers to a type of tea made from konbu (seaweed).

The moniker might be unchangeable, however, since it’s already an established international name for the drink, said Kantaro Oizumi, 37, president and CEO of Oizumi Kojo, a century-old company that used to run a casting factory and now primarily brings in revenue through real estate.

Oizumi took over the family business a decade ago and began branching out, first with imported popcorn machines, then with organic food. His business took him on frequent trips to the U.S., where he would routinely scour supermarkets to see what was trending.

“Every year, there seemed to be more drinks labeled kombucha. I tried it, and it tasted good and felt good,” he said. “I learned how the kombucha business was growing overseas, and in 2016 decided we want to get involved.”

It was then that he met Shimada, then a brewer working at sake-maker Kiuchi Shuzo’s craft beer brewery. Oizumi would soon bring him into the fold.

“I knew nothing about kombucha, but I did some research and made some of my own,” recalled Shimada, adding that the process shares many similarities to brewing beer.

Oizumi Kojo’s kombucha uses organic green tea and black tea leaves produced by Kyoto’s Nagata Chaen. The fermentation process can take a week or longer, during which the sugar and tea create a beverage with a slightly sweet and tart flavor.

Sugar feeds the yeast, creating CO2 and ethanol, and bacteria then consume the ethanol and convert it to healthy acids, according to the Kombucha Brewers International.

After initial fermentation, Shimada adds flavorings ranging from yuzu to mint and grapes. He has created about 30 flavors, some of which can be tasted at Oizumi Kojo Nishiazabu, a restaurant in Tokyo’s Minato Ward that serves the beverage on tap. Oizumi Kojo also delivers kombucha kegs to about 20 bars and restaurants that serve craft beer and hopes to expand its distribution to yoga studios, sports clubs and organic food stores.

Kombucha is a rapidly expanding industry. According to the Kombucha Market Report by Orbis Research, the global market for the drink is expected to grow from $970 million in 2017 to $3.81 billion in 2023.

The market in Japan remains subdued so far, although there are hints it could go mainstream as models and celebrities openly declare their love for the fermented drink.

“At this stage, we are the only full-scale kombucha brewery in Japan, but I think other breweries will eventually emerge,” Oizumi said.