Visiting Koji-ya Saburoemon, the only miso factory in Tokyo
Essential to various Japanese dishes, such as miso soup, nabe, and aemono salad, “miso” is a fermented food made from soybeans, salt, and koji (mold spores) and one of the traditional preserved food items in Japan. There are various kinds of miso with different sweetness, saltiness, color, and appearance. Do you know how miso is made?
I visited the only miso factory in Tokyo, which is located in Nerima City, to find out how miso is made.
After a 15 minute-walk from the South Exit of Nakamurabashi Station on the Seibu Ikebukuro Line, I could see the miso factory of Koji-ya Saburoemon in a residential area. Established in Ibaraki Prefecture in the Meiji period (1868-1912) and later relocated to this area, this miso factory has been in business since 1939.
The landmark is the sign of “Mukashi-miso.
Generally, miso making consists of three process stages, comprising “koji making,” where white rice is fermented with koji molds, “shikomi,” where soft steamed soybeans, koji, and salt are mixed and crushed together, and “jukusei,” where the mixture is set to mature. On my visit, I observed the middle stage, “shikomi.”
I arrived at the factory about 10 a.m., when the second shikomi stage was about to begin on that day. So, I rushed into the building.
I could see lots of steam coming up from a huge pressure cooker to steam soybeans. The “shikomi” on the day of my visit was for “Suzushiro no Sato,” a white miso that has been selected as part of Nerima’s recommended goods collection, “Nerikore.”
They turned off the heat and released the pressure gradually. With a loud noise of billowing steam, I could smell the aroma of soybeans spreading through the factory. There were fans to cool down the heat. Next it was time to open the lid.
They started releasing the tight locks.
The soybeans were transferred to a large space and mixed to cool down.
The workers seemed so stalwart working in the plumes of steam!
Freshly steamed soybeans. They were thoroughly prepared to remove harshness so as to be used for white miso, so they had only a slight taste of beans.
This factory only uses domestically-grown soybeans.
The next step is to mix the soybeans with koji. As the high temperature of the freshly steamed soybeans would kill koji spores, the soybeans need to be cooled down to an appropriate temperature. Since the time required to cool down steamed soybeans to a certain temperature and a certain hardness depends on the season and weather, they had to observe the soybeans while spreading out and mixing them and determine the optimal state of the soybeans, based on their years of experience as a miso maker.
The fans were working at full capacity. They said that their work is very hard in summertime as the whole factory is like a sauna.
The soybeans were cooled down to the best condition.
Dividing the soybeans into smaller pieces for mixing.
While crushing the soybeans in a stirring machine, add salt, koji, and water.
Koji with white rice
In order to promote fermentation and maturation, they next add a small amount of miso previously made. This miso is called “tanemiso” (“seed miso”), which serves as an indicator for determining the taste of the new miso. It is an important step in handing down the traditional taste.
Mixing while observing the state of soybeans. They always adjust the amount of water to add, depending on the state of the soybeans.
The soybeans became a smooth paste, which was then transferred to a huge miso tank. That was the end of “shikomi.” From this state to a final miso product, it takes three to six months of fermentation and maturation in the case of white miso.
At the end, they showed me the most important part of miso making, the koji factory. The temperature and humidity of the koji factory is controlled so that koji molds can stay comfortable. The temperature is set to relatively high at first to trigger the fermentation of the molds. Then, after the growth cycle is stabilized, ventilation is improved so that the molds won’t die out. Since it is very labor-intensive work, the amount of koji they can produce determines the amount of miso to be produced.
Fluffy koji molds growing on the surface of white rice.
They showed me some of the products produced at Koji-ya Saburoemon. The right is “Suzushiro no Sato,” for which I had observed the “shikomi” step, and the left is “Kyo no Sato,” a red miso which was fully matured for 10 months to one year. While red miso is saltier and rich, white miso is sweeter.
You can purchase the miso products by Koji-ya Saburoemon at the factory. When I was at the factory, I saw several customers visiting to buy the products. The products are also available at some shops in Tokyo as well as online shops. I highly recommend you to try miso by Koji-ya Saburoemon, which is made mostly by hand rather than by machines, using a traditional manufacturing method.
*The information herein is as of May 2021.