Usukuchi Soy Sauce : “Shoyu Nouveau”
Among Japan’s family of soy sauce, two stand out as the most widely used. Koikuchi (濃口), meaning “rich, deep-tasting,” is the one most people know and commonly refer to as soy sauce. The other, usukuchi (淡口 or うす口) is preferred in the Setouchi kitchen.
Usukuchi means “light-tasting.” It’s a “young” soy sauce, brewed and aged for one year compared to two or more years for koikuchi. This results in a lighter color and body, a fruity aroma, a slightly sweet yet refreshingly tart taste, and a milder form of umami and soy sauce flavor. It’s an ideal seasoning and sauce for fresh foods and light-tasting dishes. This includes the Setouchi’s delicately-flavored white-fleshed coastal fish, myriad shrimp, crabs, clams, squid, and octopus, as well as fresh vegetables that are available throughout the year. These ingredients don’t need much cooking, seasoning, or added richness of flavor to taste their best.
Think of usukuchi as the “shoyu nouveau” (shoyu / 醤油 being the Japanese word for soy sauce). This perspective arises from its unique flavor profile and its origins in the latter half of the 17th century as a new, refined variant of koikuchi. It’s a soy sauce that respects the main foods of a dish, subtly amplifying their aroma, color, and taste. Its saltiness and sweetness enhance their natural qualities, while its mild umami and soy sauce flavor enriches without overshadowing them, unlike the more robust flavor of koikuchi.
Owing to its culinary benefits, usukuchi is also the preferred soy sauce among Zen shojin-ryori vegetarian chefs and in the kitchens of Kyoto for both sophisticated kaiseki dishes and the more rustic obanzai home cooking.
Outside the Setouchi region and these other culinary traditions, usukuchi often remains in the shadows of its koikuchi counterpart, leading to misunderstandings and under-appreciation. A common misconception is that usukuchi translates to “light color” and should be used when one wishes to avoid darkening a dish. While this is one of its benefits, the color of usukuchi, especially a traditionally made one, is fairly dark. Often, the reason usukuchi doesn't impart as much color to dishes as koikuchi does is typically because a lesser quantity is used in recipes, compared to the more generous amounts of koikuchi used for richer dishes. Instead, usukuchi provides dishes with a subtle, appealingly toasty hue.
It's also said that usukuchi is much saltier than koikuchi. Usukuchi’s salt content of 18-19% is only a bit higher than that of koikuchi’s 16-17%, depending on the brewer. Granted, usukuchi does taste saltier than koikuchi, but that’s partly because its salty taste is not masked the way it is for koikuchi’s by koikuchi’s more intense flavor. Moreover, usukuchi’s saltier taste can be a seasoning advantage. It allows cooks to better distinguish and adjust the salty flavor of a dish, often resulting in dishes made with usukuchi having less overall salt compared to those seasoned with koikuchi.
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Usukuchi traces its origins to the Setouchi region, specifically the town of Tatsuno in Hyogo prefecture. Positioned between the renowned castle town of Himeji and the city of Ako—a longstanding hub for the Setouchi's sea salt production—Tatsuno had a strategic advantage. Beyond easy access to sea salt, the town's soy sauce brewers benefited from three other essential ingredients: high-quality soybeans from the nearby town of Sayo, locally harvested wheat given Tatsuno's location in one of Japan's primary wheat-growing regions, and pristine water from the Ibo River coursing through the town.
The finest example of 17th-century Japanese castle architecture, Himeji Castle is located east of Tatsuno City, where usukuchi soy sauce was first created during the same period.
At its core, usukuchi is made in nearly same way as koikuchi. An equal amount of steamed soy beans and roasted wheat are mixed together with koji-kin (green Aspergillus oryzae mold spores) and stored in a temperature- and humidity-controlled muro room to germinate for two to three days. The mixture is then combined with sea salt and water, creating a mash that’s transferred to large vessels for fermentation and aging.
The primary distinctions lie in the brewing duration and salt content. Usukuchi is brewed for a shorter period than koikuchi and contains slightly more salt to control and suppress its fermentation and aging processes. However, since most of the umami in soy sauce emerges during the first year of brewing, usukuchi retains an umami-rich profile. What it lacks are the deeper, more complex aromas and flavors, as well as the darker hue associated with extended aging.
While this is the standard process, specialized and artisanal brewers refine their methods to produce distinct, nuanced soy sauces. Some employ a higher wheat-to-soybean ratio, giving their usukuchi a more aromatic and sweeter profile. Others incorporate amazake, a fermented rice sweetener, for a similar outcome. To further lighten usukuchi’s color and umami, some brewers roast the wheat for shorter durations or stir the mash less often, thereby curbing fermentation by limiting the mash's exposure to air.
Each of these variations produces delightful and versatile products. The essence lies in the quality of the core ingredients. The finest usukuchi is crafted from full-fat, protein-rich, large, round marudaizu soybeans (as opposed to soybean by-products), premium wheat, and sea salt. It's also important that the soy sauce undergoes natural brewing across at least one winter and summer. Brewing in kioke wooden barrels introduces beneficial microorganisms that live in the wood, enhancing both the fermentation process and the sauce's flavor.
How To Use
Usukuchi serves as an ideal seasoning and condiment when the goal is to maintain the subtle nuances of aroma, color, and taste in foods, while also offering more control over a dish's saltiness. Using usukuchi not only adds saltiness but also provides an umami richness. Contrary to some opinions, there's no such thing as too much umami in a dish. The key lies in harmonizing the intensity of umami with the specific ingredients, cooking techniques, and other seasonings present in a dish.
Unlike some seasonings that can dominate flavors, usukuchi complements and can be integrated into various cooking styles. Its understated yet potent umami is especially harmonious with:
In the Kitchen
Stocks & Soups: Ideal for light Japanese dashi stocks as well as vegetable and chicken broths. It's also perfect for both clear and creamy soups.
Main Foods: Best with white-fleshed seafood, chicken, lean pork, eggs, tofu, and all types of vegetables.
Cooking Methods: Particularly suited for raw, blanched, steamed, and briefly simmered or braised dishes where minimal umami is derived from the cooking process itself.
Seasonings: Complements sake, light oils, butter, and fresh cheeses; sea salt; sweeteners like white cane, raw, wasanbon-to, and light brown sugars, honey, light maple syrup, and one-year aged mirin; and acidic elements like citrus juice, rice vinegar, apple cider, and white wine vinegars.
Dishes: Works well with dishes that have a light seasoning or spice profile.
At The Table
Usukuchi is versatile enough to be used at the table as a condiment. Whether dashed onto dishes or served as a dip, think of it as a blend of saltiness and acidity, enriched with umami to elevate the flavors of foods.
A dipping sauce for white-fleshed sashimi and sushi.
A condiment for chilled tofu, omelets, rice, potatoes, and dishes featuring olive oil or cream-based pasta.
An alternative to the usual sprinkle of salt and splash of lemon juice, particularly when adding the finishing touches to fried foods.
An ingredient in lightly seasoned marinades, dipping sauces, and dressings.
Once opened, it's best to store usukuchi in a cool, dark place, ideally in the refrigerator, to maintain its aroma and flavor. Nonetheless, it remains safe if left out on the counter.
Where To Buy
Usukuchi is produced across Japan by the major commercial brewers, who incorporate usukuchi into their offerings due to its integral role in numerous core recipes of classical Japanese cuisine.
Okamoto Shoyu’s Usukuchi Soy Sauce
In the Setouchi region, you can also find specialized and artisanal usukuchi brewers. Their products are commonly sold in local supermarkets, farmers' markets, and souvenir shops. Additionally, some of their offerings can be found nationwide in specialty food stores, major department store food halls, and online. Or consider visiting a traditional brewery. Each one typically features a shop at its entrance to cater to local patrons.