Homemade Miso: Crafting Japan’s Signature Fermented Seasoning

As Japanese cuisine spreads globally, traditional Japanese seasonings have also garnered attention from around the world. One such seasoning is miso, a type of fermented food made primarily from soybeans, and like soy sauce, natto, pickles, and sake, it is produced through the fermentation process involving microorganisms. Miso is a brown, paste-like food with a complex and rich flavor that blends salty, sweet, and umami tastes, commonly used in soups, stir-fries, stews, grilled dishes, and a variety of other recipes.

In Japan, fermented foods such as miso have long been known for their health and beauty benefits. During the COVID-19 pandemic, as people's attention to their daily habits and well-being increased, there was a movement to incorporate fermented foods more actively into everyday diets. As a result, more people have begun to make miso by hand, preferring it over pre-made products to ensure they are eating something that feels safer, more reliable, and personally satisfying.

So, when did people in Japan start eating miso? How can you make it by hand, and how does homemade miso differ from industrially produced miso?

In this article, I will introduce the history of miso in Japan, the method I learned at a "handmade miso workshop" for beginners, and the unique charm of homemade miso.

Miso is a simple food made from just three ingredients: soybeans, koji (a grain like rice or barley that has been malted with a special mold), and salt.

The miso we know today is believed to have originated about 1,300 years ago, using techniques introduced from China. At that time, miso was consumed in its raw form, either by dipping food directly into it or eating it on its own. It was an expensive luxury item and was sometimes used as salary for high-ranking officials or given as a gift.

During the medieval Kamakura period (1185–1333 CE), miso soup was born. By the Muromachi period (1336–1466 CE), the increase in the production of soybeans led to farmers starting to make miso by hand, spreading the use of miso and leading to the creation of various miso-based dishes.

In the Sengoku period (around 1467–1603 CE), due to miso’s high nutritional value and preservability, it was widely used as food for soldiers. Powerful warlords such as Tokugawa Ieyasu (the model for the main character in the popular drama "SHOGUN"), Toyotomi Hideyoshi, and Date Masamune encouraged miso production in their territories. Local miso varieties began to emerge, shaped by the specific regional ingredients, climate, and preferences of the area.

Later, during the early modern Edo period (1603–1868 CE), miso cuisine further developed, and miso became an essential food item in households across Japan, a tradition that continues today.

As mentioned earlier, it was around 600–700 years ago, during the Muromachi period, that ordinary people began making miso by hand.

In the agricultural society of the time, where families were large, it became standard for farm families to make a year's worth of miso by hand. This process typically took place in the winter, after the harvest, when there were fewer other farming tasks. The cold weather was thought to help prevent the growth of unwanted bacteria that might interfere with fermentation, allowing the miso to ferment slowly and develop better flavor. In reality, miso can be made year-round, regardless of temperature.

The essential ingredient for miso production, koji mold, was supplied by specialized vendors called "kojiya." In many rural villages across Japan, at least one kojiya was located in each community.

However, after World War II, the trend of making miso by hand began to fade. With the rise of nuclear families and the decline in the agricultural population during the 1960s, many people turned to factory-made, inexpensive mass-produced miso. As a result, the number of kojiya also decreased.

In recent years, there has been a renewed interest in fermented foods like miso, amazake (sweet fermented rice drink), and shio koji (salt-marinated rice malt), as their health and beauty benefits have come into the spotlight. As people began to make their own fermented foods at home again, the demand for koji grew, bringing the kojiya back into focus.

The handmade miso workshop I attended was held at Koizumi Kojiya, a long-established koji producer that has been in business since 1868, over 150 years. While the tools used were modern, we learned to make miso in a way that closely followed the traditional processes.

Since its founding, Koizumi Kojiya has continued to produce koji, and after World War II, it expanded its business to include a variety of koji-based products such as miso, amazake, and shio koji.

Koizumi Kojiya produces nama koji (raw koji), a type of koji that is fresher and more active compared to kanso koji (dried koji), which has been heated to remove moisture and extend its shelf life. Nama koji is known for its superior ability to break down nutrients and produce better-flavored miso in a shorter time.

At Koizumi Kojiya, koji is made by hand over three days in a special room called a "koji muro," located in a cool, half-underground space with stable temperatures. Using no machines, the staff follows traditional methods to create high-quality koji by hand. The benefits of using hand labor include preventing unnecessary stress on the ingredients, preserving their nutritional value, and allowing for fine adjustments based on temperature and humidity.

One sunny day in mid-February, despite it being a weekday, the small workshop was full. There were eight participants, including myself and the photographer, three Japanese women, a woman from overseas, and a couple.

One participant mentioned, "The miso we made last year was so delicious, I came back again this year," while another woman, who lives nearby and is originally from abroad, shared that this was her sixth time attending.

That day, we learned to make kome miso (rice miso), a standard type of miso made from Koizumi Kojiya's homemade rice koji and a mixture of soybeans and sea salt. The recipe used about 1.2 times the weight of rice koji to dry soybeans, bringing out the rice's sweetness and the distinctive aroma of the koji.

Now, let's walk through the steps we took to make miso.

Currently, about 80% of the soybeans used for miso making in Japan are imported, with many major miso manufacturers using soybeans imported from countries like the United States. On the other hand, at Koizumi Kojiya, they use domestically grown soybeans that are about 2.5 times larger than overseas varieties, rich in the proteins that contribute to the umami flavor. One specific variety of soybean grown in Hokkaido, called "Toyomusume," is soaked overnight to absorb water. After that, it is cooked in a large pot for four hours, until it becomes soft and fluffy. These cooked soybeans are placed in plastic bags and set on each participant's worktable.

"The soybeans used in mass-produced miso at factories may sometimes leave behind bitter compounds because the scum formed during boiling isn't properly removed," explained our instructor, Tsutsumi. "But at our shop, we take the time to carefully remove the scum, allowing the original flavor of the soybeans to stand out. These soybeans are so tender and smooth in texture that they're delicious even on their own, so feel free to try them."

I placed one of the glossy, yellowish-beige soybeans in my mouth and, just as Tsutsumi had said, it was incredibly easy to chew. There was a mild sweetness and a distinct aroma of soybeans. I couldn't help but exclaim, "Umai!" (Delicious!)

"Toyomusume soybeans have a unique characteristic: the part where the sprout, or heso (belly button), emerges is yellow, unlike other soybeans which tend to have dark-colored sprout tips. This makes the final miso visually more appealing," Tsutsumi added.

After that, I crushed about 1.7 kilograms (about 3.75 lbs) of Toyomusume cooked soybeans. I began by pressing the soybeans against the work surface through the plastic bag, occasionally flipping the bag over to ensure even crushing. It was easy to crush the beans, but it took some time to crush them all. As I worked, I checked the progress to ensure that the beans were sufficiently mashed. The more thoroughly you crush the beans, the smoother the texture of the miso will be. To finish, I worked the paste with my hands as if kneading dough, pressing it against the table until the cooked soybean paste was ready.

"Now it's time for a little exercise!" Tsutsumi exclaimed. "Grab both ends of the plastic bag with each hand, stand with your feet shoulder-width apart, and raise your arms straight in front of you. We’re going to shake the bag vigorously for 15 seconds. Ready, set, go!"

The sound of the plastic bag and paste rubbing together made a distinct rustling noise as we all shook our bags.

"3, 2, 1! All done! Great job!" Tsutsumi cheered.

When I looked inside the bag, I was surprised to see that the paste had formed a large ball about 15 centimeters (5.9 in) in diameter. This process had taken less than 10 minutes, but it was quite a physical activity, making it a good workout.

Next, we moved on to the process of mixing the rice koji and sun-dried salt in a plastic white bucket.

Before we started, Tsutsumi encouraged us to break apart the small clumps of rice koji. Inside, we found delicate, fluffy strands of mold growing like dandelion fluff. When I tried a small bite, the rice was firm but had a slight sweetness. "The enzymes produced by the koji mold break down the starch in the rice and convert it into glucose, which is why it's sweet," explained Tsutsumi.

We then scooped up the salt and sprinkled it over the rice koji, rubbing the grains together in our hands to break apart the clumps of koji mold. This process, called "shiokiri", ensures that the koji mold is killed to prevent the rice from deteriorating, and it makes the enzymes from the mold ready for use. It also helps absorb any excess moisture, preventing the growth of harmful bacteria that could spoil the miso. The result is a coarse, granulated mixture called "shiokiri koji."

We used about 350 grams (about 12 oz) of salt for this process, with a salt concentration of about 13%, which is said to bring out the umami of the soybeans and create a well-balanced miso with a clean, refreshing flavor.

Next, we mixed the soybean paste with the shiokiri koji. We worked the two together by repeatedly pressing the koji into the paste, folding and mixing until everything was evenly incorporated.

It is crucial to use all of the shiokiri koji, as it significantly impacts the final flavor of the miso. For any koji that didn't mix in easily, we would sprinkle it over the paste and press it in with our palms.

During this process, we added tane-mizu, the cooking liquid from the soybeans, in two separate stages. This liquid helps adjust the moisture level while adding additional flavor, sweetness, and aroma from the soybeans.

"While you're working, remember to say, 'Let’s make it delicious!' and have fun with it," Tsutsumi encouraged us.

When the mixture reached the consistency of a soft, firm ear lobe, the process was complete. This stage of the miso is called "shikomi miso."

We were now approaching the final stages. The shikomi miso was divided into 6–8 round balls, called "misodama," and packed into a pre-disinfected fermentation container, which had been sterilized with 35% alcohol shochu, known as "white liquor."

I used a yellow plastic barrel provided by the store, but others used transparent plastic containers that allowed for easy inspection of the contents, or black ceramic jars with distinct glaze patterns.

Each of us enthusiastically dropped our misodama into the container with a loud "thunk," making sure not to miss the target. "Be sure not to miss!" Tsutsumi reminded us. Dropping the misodama into the container in this way helps to remove any air pockets, preventing mold formation during fermentation and aging.

Afterward, Tsutsumi explained, "Take the container home and store it at room temperature, away from direct sunlight. The ideal fermentation temperature is between 25-30°C (77–86°F), so avoid placing it in air-conditioned rooms during summer."

"Even with careful preparation, mold will inevitably appear during fermentation, but due to the salt, the mold won't penetrate deep into the miso. Just scrape off the mold right before eating, and it's perfectly safe to eat."

Although the miso still had a strong saltiness at this stage, over the next few months, enzymes created by the koji would break down the rice starch into glucose, and the proteins in the soybeans into amino acids, enhancing the umami. The fermentation would also be aided by yeast and lactic acid bacteria. In about six months, the flavors of saltiness, sweetness, acidity, and umami will harmonize, resulting in approximately 3 kg (6.6 lbs) of miso with a smooth, slightly sticky texture and a rich, fragrant aroma.

"When it tastes delicious to you, that's when it's ready to eat. Mix the miso well, ensuring the consistency is even, and then store it in the refrigerator or freezer to prevent further fermentation. Miso is a preserved food, so it won’t spoil, but the flavor can change as it ages. For the best taste, we recommend consuming it within a year," Tsutsumi added.

Many mass-produced miso products available in Japan contain various additives, but with homemade miso like the one we made, you can choose your ingredients freely.

In contrast, many large manufacturers speed up the miso-making process by artificially raising the temperature during production. This can result in miso that lacks the rich fragrance and balanced flavor found in naturally fermented miso.

The difference may not be obvious until several months later, but the process of making miso by hand was an enjoyable and fulfilling experience. This hands-on approach will surely enhance the flavor of the miso. Once it’s ready, I look forward to making miso soup, savoring the aroma and taste as the steam rises from the bowl.

Additionally, koji and other ingredients can be purchased online, making it possible to create homemade miso outside of Japan. Koizumi Kojiya’s workshops are open to English-speaking participants, and even online courses are available, so if you're interested, be sure to check them out.