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The Japanese Table

Fermented Foods of Japan: Soy Sauce

by Hisakazu Iino

Fermented foods are an essential element of Japanese cuisine. They comprise seasonings such as soy sauce, miso and mirin; sake; and tsukemono (pickles)—all the delicious outcomes of various traditional fermenting processes and methods that arguably define Japan’s unique food culture. Our new Feature series will introduce several classic fermented foods of Japan, starting with one of the fundamentals: soy sauce.

Five types of Soy Sauce

Soy sauce, called shoyu in Japanese, is counted among this country’s most indispensable and versatile seasonings and is used at the table as well as in cooking and food preparation. The term shoyu actually embraces five different types of soy sauce, each of which is easily distinguished by flavor: koikuchi-shoyu, usukuchi-shoyu, tamari-shoyu, saishikomi-shoyu and shiro-shoyu.

Because of regional preferences, the production and consumption of these very distinct soy sauces vary throughout the country, and few Japanese utilize all five types. Very generally speaking, however, the seasoning commonly referred to simply as shoyu is koikuchi, which accounts for over 80 percent of all soy sauce consumed in Japan.

Making Koikuchi Soy Sauce

The main ingredients of soy sauce are soybeans, wheat, salt—and microbes. The soy sauce production process begins with the making of koji, a dry mash. After mixing steamed soybeans and wheat that has been roasted and then crushed, tane-koji (koji starter) is put in and cultured to form koji. For the koji starter, manufacturers use soy sauce koji molds such as Aspergillus oryzae or Aspergillus sojae. Koji production gives rise to enzymes such as proteases and amylases, and is an important process that greatly affects the quality of the finished product.

A salt-and-water solution is then added to the koji to create moromi mash, which is then fermented and aged for approximately six months. During the first stage of moromi fermentation, the enzymes produced by the koji mold break down the protein in the soybeans to form amino acids, which enhance umami. The enzymes also break down the starch in the wheat to form sugars, and these are what give soy sauce the elements of its unique taste and color. Lactic acid bacteria convert some of the sugar into a variety of organic acids, which generate flavor. Next, yeast goes to work converting some of this sugar into alcohol, which imparts aroma.

After some six months have passed, the moromi is pressed to yield nama-shoyu, which is raw unpasteurized soy sauce. Once this raw soy sauce has been heated, the production process is complete.

This traditional brewing process results in soy sauce that is labeled honjozo, indicating that the product is naturally brewed. Most of the soy sauce sold in Japan is of this type.

Soy Sauce and Its Uses

Soy sauce is a fine fermented seasoning renowned for its five well-balanced flavors—salty, sweet, sour, bitter and umami. And because of its high salt content, soy sauce also possesses excellent preservation properties.

Koikuchi soy sauce contains 16 percent to 17 percent salt—approximately five times more salt than seawater—yet it has no unpleasant bite. The soy sauce brewing process involves a variety of chemical changes based primarily on the action of microorganisms, and heating or pasteurizing soy sauce in order to improve its shelf life gives rise to specific characteristic aromatic and flavor constituents, along with a distinctive roasted aroma.

The origins of koikuchi soy sauce—the most popular type among Japanese consumers and best recognized worldwide as “Japanese soy sauce”—can be traced back to traditional methods of making miso, and the basics of present-day koikuchi production methods were established some 350 years ago.

A primary factor in the broader dissemination of koikuchi soy sauce was the large consumer market it commanded in the city of Edo (Tokyo), the population of which is estimated to have been one million during the eighteenth century.

During this time, not only koikuchi, but all varieties of soy sauce became popular because of their essential role in Japanese cuisine in masking the odor of fish, and for their use as flavor-enhancer and preservative. Then, as now, koikuchi soy sauce is an essential companion to sashimi and sushi: a delicious pairing of the rich flavor of soy sauce with raw fish.

Soy sauce is also used in cooking to prepare a wide range of dishes and ingredients: simmered fish, stewed meats, vegetables, soups and more. It was therefore inevitable that soy sauce should become indispensable to the daily diet.

Authentic Fermentation

Nowadays, soy sauce is sold and consumed around the world; however, there are certain soy sauce products that are not naturally brewed. These contain other processed products made with enzymes or other additives, such as chemicals that break down proteins in order to speed up fermentation.

These products have their own appeal in terms of taste, and for this reason, the industry standards for soy sauce are now under discussion by the international Codex Alimentarius Commission.

To understand the authentic and traditional taste of genuine Japanese food culture, however, one needs to taste naturally brewed soy sauce.

Author's profile

Hisakazu Iino was born in 1952. A 1975 graduate of the Tokyo University of Agriculture, since 1997 he has been a professor in the Graduate School of Science for Living Systems at Showa Women’s University. As a specialist in applied microbiology, Dr. Iino studies the interaction of human intestinal microorganisms. He also serves as an advisor to the Pharmaceutical Affairs and Food Sanitation Council, Ministry of Health, Labour and Welfare.