What Is Miso Made Of?

If you’ve ever slurped down a bowl of miso soup, you know how rich and flavorful this soybean paste can be—nutty, slightly sweet, and packed with savory umami. It’s the kind of complexity that feels like it must come from a long list of secret ingredients. But behind that big flavor is a surprisingly short ingredient list: just soybeans, salt, water, and a starter culture called koji. That’s it. Through the natural process of fermentation—and a little patience—these basics transform into one of Japan’s most beloved and versatile seasonings. Curious how it all works? Let’s take a closer look at what goes into miso paste.

Key Ingredients in Miso Paste

Soybeans

Soybeans are the key ingredient in traditional Japanese miso making. These nutrient-dense legumes are a rich source of protein, fiber, vitamins, and minerals, making them revered in Japanese food culture. During fermentation, their proteins break down into amino acids—especially glutamic acid—which gives miso its signature rich umami flavor.

By adjusting the ratio of soybeans to other miso ingredients, we can create a wide range of different types of miso. At one end of the spectrum is grain-free miso, like our Aged Black Miso, which contains a high concentration of soybeans and no grains. This results in a bold, deeply savory flavor. On the opposite end are white misos, such as our Saikyo Sweet Miso, made with fewer soybeans and a higher proportion of koji, yielding a mellow, sweet taste.

At Hikari Miso, we use only non-GMO soybeans sourced from trusted suppliers who uphold the highest quality standards from field to fermentation. Many of our products go even further, using USDA-certified organic soybeans to ensure purity and sustainability in every batch.

Koji

Koji plays such a vital role in Japanese food culture that it’s been recognized as Japan’s “national fungus.” It’s the fermentation engine behind many of Japan’s iconic foods and beverages, including soy sauce, sake, and miso. Koji is made by inoculating steamed grains or legumes with a filamentous fungus called Aspergillus oryzae. Think of it as a fermentation starter, like what you’d use to make yogurt or sourdough bread. 

To culture koji, grains like rice or barley are first steamed and then spread out in a warm, humid environment before being sprinkled with koji spores. Within hours, delicate white threads called hyphae grow across the grains, producing powerful enzymes like amylase (which converts starches into sugars) and protease (which breaks down proteins into amino acids). These enzymes are the key to miso’s deep, complex flavor and smooth texture.

During the two-day cultivation process, temperature, humidity, and cleanliness are carefully controlled to encourage healthy mold growth and prevent contamination from unwanted microbes. The result is a fragrant, enzyme-rich koji ready to bring soybeans to life through fermentation. 

Here are a few types of koji that are used to make different kinds of miso:

• Rice Koji is the most common and imparts a gentle sweetness. It’s used in our gluten-free miso products, including Organic White Miso and Organic Red Miso. Increasing the rice koji ratio relative to other ingredients creates miso with a lighter color and naturally sweeter flavor, such as our Organic Saikyo Sweet Miso.
• Barley Koji adds a rustic texture and earthy richness. You’ll find it in our Organic Barley Miso.
• Soybean Koji is used in pure soybean miso, like our Aged Black Miso. Paired with a longer fermentation time, soybean koji produces a deep, earthy flavor with a hint of bitterness.

Salt

Salt may seem like a simple seasoning, but it plays a vital role in miso. Beyond adding flavor, the salt content helps regulate fermentation by suppressing unwanted bacteria and allowing only beneficial microbes—like koji, yeasts, and lactic acid bacteria—to flourish. It also acts as a natural preservative, extending the shelf life of this fermented food without the need for additives.

Water

Often overlooked, water is the fourth essential ingredient in miso. It’s used to soak and cook the soybeans, providing the ideal environment for enzymes and beneficial microbes to do their work during fermentation. When the ingredient list is this simple, every element—even the water—matters. That’s why we source pure, soft water from the Japanese Alps near Nagano. Fed by melted snow, this pristine water is crucial for crafting our miso products.

Additive-Free Miso

For over 1300 years, miso has been a Japanese ingredient made with these four basic ingredients. While many modern manufacturers add preservatives and flavorings to their products, we believe in the natural power of fermentation to deliver a rich, satisfying miso paste with a deep flavor and many health benefits.

Soy-Free Miso

Traditionally, miso is made with soybeans, but the same fermentation process used in soy-based miso can be applied to other legumes, opening new possibilities for those with soy allergies or dietary restrictions.

Our Organic Chickpea Miso is made by substituting chickpeas for soybeans and fermenting them with rice koji and salt. The result is a soy-free miso alternative that offers the same deep umami flavor, creamy texture, and versatility that makes it—perfect for everything from soups and sauces to dressings in everyday Japanese cooking.

Now that you know what miso paste is made of, learn how miso is made, and how to use it in your kitchen.