Shoyu Explained: Japan's Soy Sauce, From Shodoshima Barrels to Noda

Nothing says Japanese cooking quite like the dark, salty, faintly sweet seasoning known as shoyu (soy sauce). It flavors grilled fish and simmered vegetables, gives noodle broth its color and sushi its dipping sauce, and sits beside the rice in nearly every Japanese home. For something so ordinary, shoyu is surprisingly complex, with five official types and a long history that stretches from medieval temple kitchens to a global brand.

This guide explains how soy sauce developed in Japan, how it is made, how its main varieties differ, and where to see it brewed. You will meet the cedar barrels of Shodoshima Island, the great producing towns of Noda and Choshi, and the practical difference between koikuchi and usukuchi, the two most common types.

A Brief History of Shoyu

Soy sauce traces back to a salty fermented condiment from China. It was present in Japan in some form for many centuries, but the tale most often told about Japanese soy sauce begins in the Kamakura period. In 1254 the Zen monk Kakushin returned from China with a method for making a fermented soybean paste, and while he taught it in Yuasa, in Kishu (modern Wakayama Prefecture), locals noticed that the liquid that collected in the vats tasted wonderful. That liquid became the ancestor of tamari soy sauce.

From there, the craft spread. By around 1580, a vendor known as Tamai is believed to have been selling soy sauce in the Kansai region, and records from 1588 mention a large shipment of tamari from Kishu to Osaka. In the Edo period (1603 to 1868), the booming city of Edo craved stronger flavors, and breweries in the Kanto Plain, especially at Noda and Choshi, began producing soy sauce locally. They still rank among the largest producers of everyday soy sauce in Japan.

How Soy Sauce Is Made

Traditional soy sauce uses four ingredients: soybeans, wheat, salt and water. Soybeans are soaked and steamed, wheat is roasted and crushed, and the two are mixed with a koji starter, the same Aspergillus mold used for sake and miso. After a few days the koji mixture is combined with brine to form moromi, a thick mash that ferments and ages in tanks or wooden barrels for months.

During that time enzymes from the koji break down proteins into amino acids and starch into sugars, producing the savory umami, the sweetness and the fragrance. The mash is then pressed to separate the liquid from the solids. The liquid is heated to stop fermentation and filtered, then bottled. Modern methods can shorten the timeline, but many artisan brewers still ferment for a year or more, trusting slow work to create layered flavor.

The Five Types of Shoyu

Japan recognizes five main categories under its agricultural standards. Koikuchi, the dark all-purpose type that originated in the Kanto region, makes up more than 80 percent of production, and it is the soy sauce you will find on most tables and in most recipes. It uses roughly equal amounts of soybeans and wheat.

Usukuchi is lighter in color but saltier, and is especially popular in the Kansai region. It makes up around 14 percent of production and is brewed with amazake, a sweet fermented rice drink, so it flavors food without darkening it, which is why it is prized for clear soups and vegetables. Tamari, made mainly in the Chubu region, is thick and rich, with little or no wheat. Saishikomi is double-brewed, using soy sauce instead of brine, for an intense flavor. Shiro shoyu is a pale, sweet type made mostly from wheat. Saishikomi and shiro together account for only about one percent of production.

Koikuchi Versus Usukuchi

The names can mislead. Koikuchi means dark flavor and usukuchi means light flavor, but the words describe color, not saltiness. In fact usukuchi usually contains more salt than koikuchi. Cooks choose it when they want to season a dish without changing its color, such as simmered white radish, egg custard or clear broth.

Koikuchi is the better choice for dipping, grilling, braising and marinating, since its deeper color and aroma enhance a dish. Regional habits matter as well. Kanto households often reach for koikuchi, while Kansai cooks keep both on hand. Tamari is often served with sashimi because of its thick body and depth, and since it contains little or no wheat it is sometimes chosen by people avoiding gluten, though anyone with a dietary need should read labels carefully.

Noda and Choshi: The Great Producing Towns

Noda, in Chiba Prefecture, sits on the Kanto Plain between the Tone and Edo Rivers. The location was ideal: soybeans and wheat grew nearby, and boats could carry the finished product to Edo. Soy sauce making flourished here from the late seventeenth century, led by families such as the Mogi and Takanashi. In 1917 several family firms merged as Noda Shoyu, later renamed Kikkoman, which became a leading force in introducing Japanese soy sauce to the world. Its classic table bottle, designed by Kenji Ekuan, dates from 1961.

Choshi, also in Chiba Prefecture, on the Pacific coast, grew into another great center. Both towns benefited from the water routes that supplied Edo, and both remain closely tied to the craft today. Visitors can learn about soy sauce production at brewery museums and factory tours in the area, though tour arrangements change, so check official sites before traveling.

Shodoshima: Soy Sauce in Cedar Barrels

On the island of Shodoshima in Kagawa Prefecture, in the Seto Inland Sea, soy sauce has been made for around four hundred years. A small number of artisan brewers remain, many near the island's town center, and some still ferment moromi in huge wooden barrels made of Japanese cedar that are more than a century old. Artisan batches may age for two to three years, far longer than most commercial soy sauce, and the old barrels are a large part of the island's character.

Visitors can tour a brewery, see the barrels through a window or on a guided walk, and taste soy sauce in different grades. Some shops sell unusual soy sauce products, including soy sauce soft-serve ice cream. Reaching the island takes a ferry from Takamatsu or another mainland port, and the trip fits neatly with a visit to nearby Naoshima or an udon tour of Kagawa.

How to Use and Enjoy Shoyu

For dipping sushi and sashimi, pour a small amount into a dish rather than a full pool, and use only as much as you need. With sushi, dip the fish side rather than the rice. Plain white rice is traditionally eaten as it is, so avoid pouring soy sauce over it at a restaurant, where it can mask the delicate flavor of the grain.

To bring home a bottle, look in supermarkets, department stores and specialty shops, and consider a small set of different types to compare. Keep opened bottles in the refrigerator for the best flavor, especially for light or fresh-pressed types. Check labels for allergens, since soy, wheat and sometimes alcohol are ingredients, and if you plan a trip to a producing region, confirm opening hours and tour times on official sites before you set out.