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Japan’s First Woman Soy Sauce Sommelier Is Here to Help Save Tradition

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Kuroshima, a native of Shodoshima, returned to the island in 2009, and is helping to preserve the island’s traditional soy sauce production methods.

Courtesy Keiko Kuroshima

Kuroshima, a native of Shodoshima, returned to the island in 2009, and is helping to preserve the island’s traditional soy sauce production methods.

Keiko Kuroshima is one of just three soy sauce sommeliers in Japan.

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Shodoshima, Japan, is a chicken foot–shaped holm in the Seto Inland Sea whose name means “Island of Small Beans.” Sleepy but serene, it is best known in Japan for its stretch of soft white sandbar that links the main island to three tiny islets and for its olive groves, which fan across the south coast. (Shodoshima is the first area in Japan to grow olives, and Milos, Greece, is its sister island.) Since ancient times, it has also been a major soy sauce production center; it is estimated that as many as 400 soy sauce “breweries”—where production happens—covered the island during the Meiji era, which stretched from 1868 to 1912. But for Keiko Kuroshima, who grew up on the island, Shodoshima’s small-town, traditional feel was something to escape. 

“When I left Shodoshima to go to university, I thought I would never come back,” says Kuroshima. “When I was a child, I found life in the countryside boring and stifling. Every day I thought, ‘I want to get out of here as soon as possible.’ But that was because I was unaware of the beautiful intricacies of its people, culture, nature, and food.” 

It was only after Kuroshima left Shodoshima that she began to consider returning: In 2004, she was a third-year college student in the Department of Information Design at Kyoto University of the Arts, learning how to “convey information” and “master expression.” Kuroshima thought about the nexus of those concepts and realized that in order to show real truth in her artwork she needed to learn more about her own life and where she had come from. And so: back to Shodoshima she went, to stay at her childhood home near Hishio no Sato, or “Soy Sauce Village,” which comprises 14 of Shodoshima’s 19 remaining traditional soy sauce breweries. “Many of my neighbors and relatives work in the soy sauce business, so ‘researching my hometown’ became ‘researching soy sauce’ as well,” says Kuroshima. 

As is so often the case, what Kuroshima once took for granted she began to appreciate with more space and perspective. During those weeks in 2004, she visited local breweries for the first time, surprised by the individuality she found. “Each one has a different idea of what they want to create, and the brewery and soy sauce embodies their ideas perfectly,” she says. “My visits to these local breweries and discussions with the breweries completely changed how I viewed my hometown and my neighbors and relatives.” Where there was once a sense of subtle chagrin at being from such a small island, there was burgeoning pride in the preservation of the traditions of one of Japan’s most indispensable condiments. Kuroshima, in her words, was “mesmerized.” 

“My visits to these local breweries and discussions with the breweries completely changed how I viewed my hometown and my neighbors and relatives.”

Kuroshima returned to university, and after graduation in March 2006, worked in Tokyo and Takamatsu City to learn about soy sauce and communicating its intricacies to the world. In 2009, Kuroshima passed an exam from the Nihon Shoyu Gijutsu (Japan Soy Sauce Technology Center) to be a soy sauce sensory inspector and was also named a sommelier; that same year, she returned to her home island to begin work, joining fellow inspectors on their monthly evaluations of soy sauce breweries of Shodoshima to ensure quality is being maintained.

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Even in soy sauce–crazed Japan, where the condiment is used for everything from flavoring nimono stock to serving as an accompaniment to the world’s best sushi, Kuroshima is the world’s first woman soy sauce sommelier and one of just three in the country. “My job is akin to searching for local treasures,” says Kuroshima, whose Japanese-language book on soy sauce was released in 2015. “Soy sauce is not something enjoyed on its own, so it’s important to connect it with local ingredients, cuisine, and people.”

Thought to have been invented in China sometime around the third century, soy sauce came to Japan in the seventh century along with Buddhism. Known in Japan as shoyu, Japanese soy sauce differs from Chinese soy sauce—which is traditionally 100 percent soy—primarily in that it is a blend of wheat and soy, which gives it a sweeter, “more nuanced” flavor. 

To make soy sauce, roasted wheat and steamed soybeans are combined with a koji mold and then mixed with salt and water to create what is called moromi—the fermented slurry that is the sum of all parts. Manufacturers looking to cut corners will use wheat bran or flour instead of wheat, mix the moromi with hydrolyzed vegetable protein, and only age the moromi one month before pressing, heating, and adding additives to the condiment like caramel, sugar, and preservatives. But to be considered honjozo, the traditional brewing method regulated by Japanese law, soy sauce must be relatively untouched; the “natural power of microorganisms” serve as the source of most of the flavor. 

Differences in the quality of soy sauce can be judged by four primary factors: color, viscosity, smell, and taste. Soy sauce with color additives will change the color of food, while traditional soy sauce should be transparent when placed in a white dish. Traditional soy sauce will give off sweet and savory aromas, while heavily processed soy sauces will smell one note: sharp. Traditional soy sauce will taste equally sweet and salty, and slide right off a chopstick like a diver slipping into a pool, unlike chemical-heavy sauce, which forms a thick droplet and refuses to hop off the proverbial diving board.  

In Japan, more than 80 percent of soy sauce is produced using honjozo standards, but even within the designation, there are differences, Kuroshima says. Although the ingredients in the soy sauce may be the same, large companies produce their soy sauce in stainless steel tanks and control the temperature artificially, instead of letting their soy sauce ferment in traditional wooden vats called kioke. Consider: A commercial soy sauce from Kikkoman takes three to six months to produce. Shodoshima’s thousand-liter wooden vat-brewed soy sauce takes an average of one to two years; some, like Yasuo Yamamoto of Yamaroku Soy Sauce, age their barrels for four years. (Kikkoman does retain several kioke to produce soy sauce for the emperor and the imperial family, per the BBC.) Of the 3,000 kioke still used to make soy sauce in Japan today, more than 1,000 of them are on Shodoshima. 

Much like with barrel-aging spirits, “brewing” soy sauce in these traditional wooden drums—where the wood grain plays host to millions of happy microbes—changes the flavor, allowing traditional soy sauce artisans to offer a product that is touched by little else than the alchemy of sun, wind, time, and mold. Of course, several of these factors vary by destination, and the age of the wood kioke comes into play, too. “Soy sauce also has its own quirks, which is why it has a unique regional flavor,” says Kuroshima.

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Still, in a country with roughly 1,500 soy sauce producers, less than 1 percent of soy sauce in Japan is still produced this way. In large part, this is simply due to supply and demand: Consumers want and consume more soy sauce than can be produced by small-batch artisanal purveyors. (In 2019, the global soy sauce market was valued at $40.63 billion; by 2027, estimates from Fortune Business Insights put it at $56.67 billion.) Building kioke is also a disappearing art, with one lone commercial company, Fujii Seiokesho outside of Osaka, still in business. 

It is largely for this reason that in addition to her work on Shodoshima, Kuroshima regularly travels around Japan to taste and collect soy sauces from every traditional maker so that she can continue learning and pushing awareness of the disappearing traditions forward; she has said she will only discuss a soy sauce after she has “visited the manufacturer, bought the soy sauce, tasted it, and used it in my cooking.”

Though koikuchi—a veritable mix of light and dark soy sauce—is what you’ll find in most Japanese fridges, as it accounts for more than 80 percent of all soy sauce sales in the country, Kuroshima is hopeful that her work will help change the public consciousness, or at least empower consumers to make a more informed choice about regional specialties. Because regional specialties not only tell a story about the ingredients but they also provide clues into the regional cuisines, too: In the Kansai region, where ingredients are celebrated for their ability to shine stand-alone, dishes like yudofu (hot tofu) are commonly paired with usukuchi soy sauce, which has a higher salt content and a lighter color. Likewise Shiro soy sauce, which is sweeter, made with more wheat, and produced in the Aichi prefecture near Nagano, is a perfect complement to the region’s famous Nozawana pickles. 

Prepandemic, Kuroshima brought visitors interested in learning more about soy sauce behind the scenes of Shodoshima breweries themselves. (“It’s much easier to understand the soy sauce–making process once you’ve experienced it firsthand versus just reading about it,” she says.) Via connections with local tour groups and guides, she also ran workshops with soy sauce tastings, prompting attendees to examine the color, aroma, and flavor of select sauces and comparing the different brewing methods, preparation containers, and the best-suited soy sauces for various diets and allergies. 

And while Kuroshima in 2020 traveled around Japan for soy sauce much less frequently than in years past, at the end of the day, she is grateful to have come full circle: to have returned home to the little island she thought she’d left forever, where her quest for self-discovery continues parallel to her career as a soy sauce sommelier. 

“The more work I do, the more I encounter the island’s charms, one after another,” says Kuroshima. “The more I learn about the local area, the more fulfilling my work becomes. My own life has become richer.”

One of the many traditional soy sauce breweries on Shodoshima

Where to Taste Soy Sauce on Shodoshima

Yamaroku Soy Sauce 
One of the most notable soy sauce breweries in the country, Yamaroku also makes its own kioke. (No reservation required; open year round.)

Shokin Soy Sauce 
Per Kuroshima, Shokin soy sauce has a power that enriches the delicate flavors of ingredients such as dashi, vegetables, and white fish. (Reservation required; weekdays only.)

Yamahisa
A pioneer of organic soy sauce in Japan, Yamahisa has produced soy sauce on Shodoshima since 1932. (Reservation required; open weekdays and second and fourth Saturdays of every month only.)

Marukin Soy Sauce Memorial Hall
This museum displays tools and materials used in traditional soy sauce making. Be sure to check out the “Natural Brewing Storehouse Gallery Stage,” says Kuroshima.

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