How Is Miso Made? Ask Paul

And what are the different kinds?

Published Oct. 25, 2023.

Outside of Japan, miso is familiar as the seasoning in miso soup but is somewhat rarely seen in other contexts. Considering how varied and how flavor-packed miso is, that’s too bad. Let’s look at some of the varieties and where they come from.

What Is Miso?

Miso is a paste made by fermenting soybeans, rice and/or barley, and occasionally other grains and nuts. Like sake, soy sauce, and numerous other foods, the fermentation is done with the help of koji.

Koji, or Aspergillus oryzae, is a type of fungus that breaks down starch into sugar and protein into amino acids. The amino acids—particularly glutamic acid—provide a wealth of umami taste, and the sugar serves as food for numerous other fermenting organisms that contribute an array of further complexity to the flavor of the finished product.

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How Is It Made?

Koji is the name of both the organism and the culture grown from it. So the usual first step in miso-making is to steam rice and/or barley, add a dose of starter koji (the organism), and let it grow for a few days to fully colonize the grain or beans and form koji (the flourishing mold culture).

That is then combined with cooked soybeans, mixed with salt and water and sometimes additional helpful bacteria, and allowed to ferment for anywhere from a week to a few years. The time, the base ingredients, and the details of the process are what make the difference between the different varieties of miso.

What Are The Types of Miso?

Red miso, also known as akamiso, may be the most familiar type. It starts with a koji culture mixed with soybeans, and it develops its brownish-red color over a year or more of aging. In order to repel hostile microorganisms during that long stint, red miso is made with a higher proportion of salt—and hence tastes saltier—than most other varieties. Red miso is commonly used in miso soups, on its own or in combination with a lighter miso.

Some red miso is made with brown rather than white rice and is known as genmai miso. The rice bran thus included gives it an additional nutty complexity.

White miso is also known as shiromiso, which is Japanese for “soup miso,” although the soup it makes on its own is not as complex as soups that include red miso. It is fermented for a much shorter period, sometimes as little as a week, and contains a higher proportion of rice, which gives it a mild, somewhat sweet flavor.

Yellow miso, or shinshu, is made similarly to white miso, but it’s aged for several weeks longer and has a deeper flavor and color. Alcohol is often added to yellow and white miso to help preserve it—and even in cases where alcohol is not added, some alcohol is created naturally during the fermentation process.

Hatcho miso is unique in that it contains no grains, only soybeans. The initial koji fermentation starts with soybeans only, and it requires a multi-year aging process under weights, which concentrates its flavor, color, and texture into a dense, chocolate-colored delicacy.

Some of the many other varieties of miso are made with primarily barley, with buckwheat, and with millet.

During the production of miso, the soybeans shed a deep-brown salty liquid. This runoff is tamari, a type of soy sauce.

Ask Paul Adams, senior science research editor, about culinary ambiguities, terms of art, and useful distinctions:


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