Kamose, a private cooking studio run by fermentation specialist Nobuaki Fushiki, is hidden among the backstreets of Tokyo’s Gakugei Daigaku district. Fushiki’s special dinner events, which feature an array of fermented ingredients, have a clandestine quality that brings to mind the speakeasies of the Prohibition era. Entering through the back of the residential building that houses the studio, guests speak softly to avoid disturbing the neighbors. As at some of the city’s small, exclusive restaurants and supper clubs, reservations at Kamose usually require an introduction. Seats for the dinner events fill up quickly, but the website lists no phone number.

Inside, large vats of homemade soy sauce and dark brown hishio — a thick mixture of fermented grains and salt, often referred to as the predecessor of miso and soy sauce — sit quietly bubbling in one corner of the room. A whiteboard conceals the tiny kitchen, from which Fushiki emerges carrying the first course: ika no shiokara (fermented squid entrails) made with hishio, served with slithery junsai (a kind of water plant), lightly marinated in hishio and tart ponzu (citrus sauce).

Fushiki is in his late 30s, with a compact frame and a closely shaven head that give him the appearance of a Shaolin monk. A chef with over 20 years’ experience, he began studying traditional Japanese fermentation techniques five years ago and has since become one of the leading figures in the recent boom in Japan. At Kamose, he holds fermentation workshops where students can learn about the history and science behind the process, as well as how to make amazake (sweet half-sake), miso and soy sauce. An outspoken commentator on the NHK radio show “Suppin,” Fushiki has authored eight books on the topic and speaks about fermentation’s ability to “completely transform ingredients” with the fervor of an evangelist.

“Fermentation refers to more than cooking,” he says. “It’s the story of the coexistence between human beings and microorganisms, and an important part of Japanese culture.”

Though once a common practice in the Japanese kitchen, fermentation has largely disappeared from the repertoire of many home cooks. The last five years, however, have seen a revival of interest — both in Japan and around the world — thanks in part to the popularity of shio-kōji, rice inoculated with Aspergillus oryzae, which is used as a seasoning for meats and fish to enhance their flavor and to tenderize them.

The purported health benefits of the live cultures found in fermented foods, Fushiki says, have played a major role in driving the boom: “People are interested in foods that promote health and beauty, and fermented foods support the gastrointestinal and immune systems.”

Japanese food expert Elizabeth Andoh, who writes in depth about traditional pickling techniques in her book “Kansha,” points to other reasons behind the trend. “After the earthquake and tsunami disaster (in March 2011), there was a sense of panic and concern, with people looking again at where food comes from,” she says, before adding that many modern cooks are now turning to “the wisdom of the ancients in the kitchen.”

But those experimenting with fermentation at home, Andoh notes, should proceed with caution. “It’s not something everyone should be doing in their back room,” she says. “You need to understand chemistry and be aware of the changes that take place during the process.”

Fushiki agrees. When I tell him that I want to enroll in his next soy-sauce-making class, he shakes his head.

“You can take the most basic class, amazake,” he says. “You have to walk before you can run.”

For more information on the Kamose cooking studio, visit www.kamose.co.jp

Don’t get into a pickle

When fermenting foods at home, the most important thing, says Japanese food expert Elizabeth Andoh, is overall kitchen hygiene. “Raw tofu can be equally as dangerous as raw chicken on a cutting board,” she warns. To avoid potential microbiological mishaps, make sure that all of your surfaces, containers and tools are meticulously clean.

Choose containers with non-reactive surfaces such as glass, enamel-lined metal or glazed ceramic. The fermentation process can leach chemicals and other unwanted compounds out of plastic. Sterilize containers with boiling water and dry before using.

Avoid fluctuations in temperature. Heat affects the growth of microorganisms, and while frigid conditions can kill fragile good bacteria, sudden changes in temperature can yield a similar result. The ideal temperature for most fermented foods is between 15 and 18 degrees Celsius.

Monitor the process carefully. Check the moisture levels and “fizz action” at least once a day. Vigorous bubbling is a sign of rapid fermentation and can be controlled by lowering the temperature. If pickling in a nuka pot, be sure to stir the rice-bran paste by hand to aerate it and prevent the buildup of harmful butyric acid.

Don’t fear the funk. “There’s a difference between spoilage and fermentation,” Andoh says. Strong, cheese-like aromas are common, but beware putrid ammonia smells. Likewise, the presence of mold is not always disastrous: White mold on the surface of fermented food is usually harmless and can be safely scraped away. Blue or green mold may pose problems for those with penicillin allergies, but pinkish growths are always toxic — a sign that the pickling medium should be discarded.

In line with COVID-19 guidelines, the government is strongly requesting that residents and visitors exercise caution if they choose to visit bars, restaurants, music venues and other public spaces.

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