Flavor made by microbes
Many of the flavors people think of as typically Japanese come from fermentation: the slow transformation of food by microorganisms. Miso, soy sauce, mirin, rice vinegar, pickles, natto and even dried bonito all owe something to it. Fermentation preserved food before refrigeration and also created new tastes, deeper and more savory than the raw materials.
Fermentation is not unique to Japan, and similar traditions exist in many countries. What is distinctive in Japan is how many of its basic seasonings are built on one particular organism.
Koji, the quiet workhorse
That organism is koji, a mold, Aspergillus oryzae, that is grown on steamed rice, barley or soybeans. As it grows, it produces enzymes that break down starches into sugars and proteins into amino acids. In other words, koji does the work of unlocking sweetness and savor. This is why koji is central to miso, soy sauce, mirin, sweet rice drinks and sake brewing.
Koji has been used in Japan for a very long time, and many people regard it as a kind of national microbe. Whatever the symbolism, it explains why Japanese cooking so often leans on a set of related fermented seasonings, which combine to give food what many describe as a rounded savor.
Miso
Miso is a paste made from soybeans, koji and salt, which ferments for months or longer. Many varieties exist. The koji may be grown on rice, barley or soybeans, and the paste can range from pale and sweet to dark and strongly flavored. A few general patterns are often described:
- Shiro (white) miso, usually shorter fermented, lighter in color and milder or sweeter.
- Aka (red) miso, usually fermented longer, darker and saltier.
- Mugi (barley) miso and mame (soybean) miso, associated with certain regions, with distinct flavors.
Regional preferences are strong, and a household’s choice of miso often reflects where it lives and what it grew up with. The most familiar use is miso soup, which combines miso with dashi stock. Miso is also used in marinades, dressings, glazes and pickling beds. Because it is concentrated, only a small amount is needed.
Soy sauce
Soy sauce, shoyu, is made from soybeans, wheat, salt and koji, fermented in a mash and then pressed to extract the liquid. Its history is generally traced to earlier fermented pastes, and the sauce took on its modern form over several centuries. By the Edo period it was widely used, and its production grew into a major industry. Edo townspeople ate out at stalls and shops that relied heavily on the sauce, and it became part of the city’s food identity.
There are several common types. Dark soy sauce is the standard, all-purpose kind. Light-colored soy sauce, which is actually saltier, is used where cooks want to preserve the color of ingredients. Others, such as tamari, are associated with a thicker body and a lower proportion of wheat, though definitions vary and labels should be read if a dietary restriction applies. Soybeans and wheat are common allergens, so anyone with an allergy should check ingredients carefully.
Other fermented foods
- Mirin is a sweet cooking liquor made with rice, koji and alcohol. It adds sweetness and gloss to sauces and glazes.
- Rice vinegar is made by a second fermentation of an alcoholic rice liquid, and it seasons sushi rice and dressed dishes. Fermentation also runs through the early sushi history, since the oldest forms of sushi were fermented fish.
- Tsukemono, or pickles, may be made with salt, rice bran, vinegar or sake lees. They are a standard part of the traditional meal and can provide a bit of sourness and crunch.
- Natto is soybeans fermented with a bacterium. It has a strong smell and a sticky texture, and tastes vary: many people in Japan love it, others do not, and its popularity differs by region.
- Katsuobushi, the dried bonito used in dashi, is treated with mold during curing and becomes extremely hard.
- Sake and its by-products also draw on koji, as explained in the discussion of sake brewing.
Salt, time and caution
Most of these foods are salty by design, since salt controls which microbes grow. This explains their long shelf life, and also why they should be used in moderation. People who have been advised to limit salt, for example for medical reasons, should ask a qualified health professional what is suitable for them. This article does not promise health benefits from fermented foods.
How fermentation shaped cooking and taste
Fermented seasonings give Japanese cooking its foundation. A simmered dish may combine soy sauce, mirin and dashi, a dressing may use vinegar and miso, and a meal may close with rice, soup and pickles. The result is a cuisine that builds depth with a small set of related ingredients. This links directly to umami, the savory taste that many of these foods are rich in.
Fermentation is also tied to the calendar. Households and small producers traditionally prepared miso and pickles during certain seasons, and the work was often done in the cold months when conditions favored slow aging. Making these foods was a rhythm of the year, much like the seasonal cycles of the farm and the table.
Tradition and change
Today, most people buy miso and soy sauce from producers, from large factories to small makers who still use wooden barrels. Home miso making survives as a hobby and a family tradition. Whether made at home or in a factory, the underlying idea is the same: time, salt and living organisms transform simple crops into something more complex, which is part of why the tradition has remained at the center of Japanese food.