Over a period of months or sometimes even years, koji ferments the soybeans to yield a deep umami flavor.

In the case of miso, koji grows on the rice, barley, or another grain before it’s added to the soybean mash to start the fermentation process. “Koji’s protein enzymes break down the protein in the soybeans and create amino acids,” explains Mariko Grady, owner of San Francisco–based Aedan Fermented Foods. This ancient fungus appears in countless East Asian fermentation practices: It’s the “starter” used to ferment miso, soy sauce, sake, rice vinegar, and shōchū. No matter what type of miso you’re dealing with, it all starts with a mold spore called Aspergillus oryzae, also known as koji. Accordingly, wealthier merchants could afford to purchase more expensive miso made with rice, whereas farmers and townsfolk often ate miso made with millet, barley, or other common grains. “Traditionally, rice miso is more expensive than barley miso, because the grain is more expensive,” explains Chung. The emergence of a wealthy merchant class in major Japanese cities like Kyoto and Edo (now called Tokyo) led to an increase in demand for high-grade miso. Still, class stratifications remained apparent in the trade and purchasing of miso. The onset of the 17th century brought about the industrial production of miso, propelling the nutrient-dense soybean paste to widespread popularity. Today, rice and miso soup remain a popular Japanese breakfast. In the 12th century, miso soup-which used a small amount of the precious paste to flavor dashi, a Japanese broth-became a dietary staple of Kamakura samurai. At first, miso was considered a delicacy, only available to Japanese nobility and monks-they ate the fermented paste either as a spread or on its own. According to the Japan Miso Promotion Board, miso was first introduced in Japan in the 7th century. Though miso has become emblematic of Japanese cuisine, the ingredient is believed to have originated in China or Korea. It’s a vital ingredient in Japanese cooking, often used to bring a wallop of savory flavor to soups (like miso soup and hot pot), noodles, and yakitori dishes. In fact, over 1,300 variations of the umami-rich paste are in use today. Factors like the type of koji used and the length of fermentation can result in infinite varieties of miso, including some that contain no soybeans at all (more on that below). Miso, a.k.a. fermented soybean paste, is made by combining just three simple ingredients-soybeans, salt, and koji (a type of fungus cultivated on rice and other grains)-and allowing the mixture to age for months or even years. But before we dive into all the kinds of miso you may spot at the supermarket, let’s start with the basics. But what is miso exactly? And how can you incorporate it into your own cooking routine? Below, we’ll guide you through a few of the many, many varieties of miso available around the world and talk about a few of our favorite ways to use each one. In recent years, the fermented staple has grown in popularity across the globe, dressing tangles of glossy spaghetti and adding nuanced flavor to baked goods.

For centuries, miso has claimed a central spot in the Japanese culinary canon.

Best white miso paste