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Let Us “Shoyu” the Wondrous World of Soy Sauce

December 12, 2016

Breaking the Mold

In many countries around the world, moldy food is likely to be greeted with dismay, a sign that the item in question is spoiled and no longer edible. Japan’s chefs, however, have successfully harnessed the many molds, bacteria and yeasts that thrive in the nation’s warm, humid summers to develop a wealth of dishes and condiments produced through microbial action.

The benefits of this approach are manifold. Microorganisms secrete enzymes that enhance flavor by breaking down starches into sugars, and amino acids and nucleotides into umami-rich compounds like glutamic acid and inosinic acid to produce the characteristic flavors that lie at the heart of Japanese cuisine. Fermentation can also serve to preserve perishable foodstuffs through sticky summers and harsh winters.

Of all the species cultivated for such purposes, perhaps the microbial jewel in Japan’s culinary crown is aspergillus oryzae, more popularly known as koji mold.

This filamentous fungus occurs naturally on rice, Japan’s staple crop. First employed by Chinese gourmands over two thousand years ago, in Japan koji is vital not only to the saccharification of rice in sake brewing but also to the production of two key Japanese condiments: miso paste, and soy sauce (known in Japanese as shoyu).

With an astonishing 1.1 million kiloliters of Japanese-style soy sauce consumed around the world each year, most readers will surely be familiar with this indispensable condiment, which is produced by applying the magic of koji mold to a surprisingly simple list of ingredients: soybeans, wheat, salt, and water.

First, the beans are steamed and combined with roasted wheat, before koji spores (koji-kin) are added to the mixture as it is evenly raked out across a wide board in a special room designed to maintain a high humidity. Left here for three days, the mold multiplies to create a furry bean culture: koji, the essential base of soy sauce.

The koji is transferred to a vat where it is mixed with salted water, producing a pulpy brown mash called moromi. After several months, or even years, of aging and fermentation (traditionally in gigantic wooden tubs) and regular stirring to promote aeration, the moromi is portioned into sheets of fine muslin cloth.

Each bundle is carefully wrapped, before they are stacked in up to 80 layers, and pressed to expel the raw soy sauce within. The process is completed by simmering these juices over a fire to halt fermentation and stabilize the flavor.

An Essential Ingredient

Despite the global popularity of soy sauce, even those with an interest in washoku (Japanese cuisine) may not be fully aware of quite how many Japanese dishes rely on shoyu, nor the extent to which it has shaped the evolution of this country’s cuisine since its probable introduction from China by Buddhist monks in the seventh century.

It is, of course, the essential dipping sauce when enjoying sushi and sashimi. And as sushi developed into the form most recognizable today in the early 1800s, soy sauce was also simmered together with mirin (rice wine vinegar) to make nikiri, a thick brown condiment that the sushi chefs of old Edo (modern day Tokyo) would daub onto each completed morsel.

Since those days, before the advent of refrigeration, sea produce including shrimp and shredded konbu kelp has been preserved by simmering in soy sauce and mirin to produce easily-transportable tsukudani, which are often served as side dishes. Repeated coats of shoyu are also applied throughout the grilling of eel skewers and yaki-onigiri rice balls.

Especially in the winter months, soy sauce defines the flavor of hearty nabe and sukiyaki hot-pots. And where would Japanese noodles be without the shoyu-based broth in which warm soba and udon are served, or the dipping sauce that accompanies chilled varieties?

Soy sauce is also essential in balancing out the palate of numerous dishes served over piping hot white rice, including tororo (grated nagaimo yam), natto (sticky, fermented soybeans, usually cut with scallions and mustard), and tamago-kake-gohan (or TKG for short, a popular breakfast item consisting of raw egg stirred into a bowl of rice).

Regional Variation

In fact, the range of dishes underpinned by soy sauce is almost rivalled by the staggering array of regional shoyu varieties that have developed in response to local differences in weather, culture, crops, and even tastes.

Nonetheless, the output of an estimated 1,600 individual breweries nationwide can be broadly divided into five principal categories that each lend themselves to particular uses: dark (or koikuchi), light (usukuchi), white (shiro), rich (tamari), and specially fermented (sai-shikomi).

Koikuchi soy sauce, which accounts for 80% of domestic production, spread around Japan from the Kanto region (surrounding modern day Tokyo and Yokohama) as the population rapidly grew and culture of all sorts flourished during the peace and prosperity of the Edo period (1603-1868). With a particular profusion of breweries in Chiba, to the east of Tokyo, shoyu drove the evolution of emerging staples like sushi and tempura.

The more genteel citizens of the Kansai region, meanwhile, favored the paler usukuchi variety. More mellow in flavor, this light soy sauce is ideally suited to refined Kyoto dishes like yudofu (tofu and vegetables simmered in broth) and elegant Kyo-kaiseki course dining that emphasizes the natural qualities of the ingredients themselves. Lighter and subtler still, is shiro soy sauce, which is favored for pale soups and chawan-mushi, a savory egg custard.

Richer, thicker tamari soy sauce has historically been more popular in Japan’s central Chubu region. Thought to be similar to the earliest soy sauce varieties introduced from China as a byproduct of miso fermentation, this variety contains little or no wheat, and so can even be suitable for those with gluten allergies. It is an ideal accompaniment for sushi and sashimi, and also used in the production of senbei rice crackers.

Sai-shikomi or specially fermented soy sauce replaces the salted water added to the koji soy mix to produce moromi with ready-made koikuchi shoyu. Widely made in southwest Japan, the dark color and potent flavor make this variety a popular choice as a tabletop seasoning.

Text: David McMahon