Rice for Koji vs. Rice for Sake and Miso

Marika Groen

March 18, 2022

Last October, American food professionals visited fermented food producers to deepen their knowledge of Japanese fermentation culture during the “Hakko Tourism in Japan” tour campaign. As part of the tour, organizers held a tasting session where guests gave candid advice from the perspective of the American market to food product manufacturers looking to enter the United States market.

Now that koji is being produced all over the world, the substrate can be bread, vegetables, fruit, all kinds of grains and legumes, and the push for a new koji culture knows no bounds.

However, as a koji maker who has worked across Japan and Europe, I see that there is a big difference between koji made from rice available in Japan and the one from rice varieties available in Europe. Actually, there are many different varieties of rice, even within Japan, so it may be more accurate to say that the difference depends on the variety and growing conditions of the rice, rather than on national borders.

Recent research has shown that the starch composition of rice is related to its melting ease, which is related to the temperature during the first 40 days after the rice has emerged from the grain.
The rice used to make sake is milled in different proportions depending on the grade of the final sake product, but there are two main types of rice: rice used to make koji and “kakemai”, which is added when the mash is brewed. About 70% of the rice used in sake brewing is used as kakemai, and this kakemai, dissolved in the moromi, is the original form of sake.
In fact, until around the Muromachi period (1333-1573), it was difficult to polish the rice itself, and it was common to use unpolished brown rice for koji rice and polished rice for kakemai in a cloudy sake called “katahaku”.
Rice on green cloth
Today, turning brown rice into white rice can be done easily with a rice-polishing machine, but in the Muromachi and Edo periods it was very difficult, with a foot-powered rice-polishing machine producing at most 8% of the rice.
Rice milling using a water wheel, which utilises water energy, made dramatic progress and flourished in the Nada region, which is famous for its sake, and is said to have reached its peak around the middle of the Meiji era (1868-1912). It reached its peak around the middle of the Meiji period, when it was possible to polish rice to 15%.
Meanwhile, the introduction of steam engines during the Meiji period led to the spread of power-driven rice milling machines, and the invention of the revolutionary vertical grinding milling machine, which polished the surface of the rice with a rigid roll, made it possible to produce white rice with a high polishing ratio, similar to that of today. As a result, the ‘morohaku’ type of low-acid sake, in which both koji and kakemai are made from polished white rice, gradually became the major type of sake.
Rice produced specifically for the purpose of sake brewing is called “shuzo-kohteki-mai”. The word “sakamai” refers to all rice used for sake brewing and therefore includes common rice.
Sakamai is characterized by a larger “shinpaku” (an opaque white portion in the middle of the grain), than rice used for food. Shinpaku contains a large amount of starch and is highly viscous, which plays an important role in koji making. The surface layer of the rice also contains proteins and vitamins, which are the source of miscellaneous flavors, so it is necessary to polish the surface layer during the sake brewing process. Shuzo-kohteki-mai is made in advance so that the heart white is large, and is truly rice for sake brewing.
Ear of rice

Now, what about the rice used for rice koji for making miso?

Most of the time, we use rice that has been polished to about the size of regular rice (about 90%). We call it table rice. My theory is that if you use rice that tastes good to eat as koji, your miso will also taste good. There are also several breweries that make delicious sake using table rice as well.

Rice koji for miso is of course mixed with soybeans, after which it is fermented and matured, breaking down the nutrients in the soybeans, mainly protein, to make the mixture into miso.

Protease, an enzyme that breaks down proteins, plays an active role in this process. In order to expect this from rice koji, the proteins in the rice must be eaten by the koji fungi when the rice is turned into koji. When the koji fungi eat the proteins in the rice, they produce enzymes from the tips of their mycelium to dissolve the nutrients. That is protease.

Since the proteins in the Uruchi rice are distributed evenly throughout the rice, it is easier for the koji fungi to produce enzymes that dissolve them as they multiply. This means that the koji will be suitable for making miso as a consequence.

Incidentally, brown rice can also be used as koji for miso. In this case, koji making and fermentation and maturation of the miso tend to take longer than in white rice koji miso because brown rice contains more nutrients to decompose.

When making koji from brown rice, sprout the rice first or polish it slightly to make it easier for the mycelium of koji fungi to grow inside, thereby creating an opening for the mycelium. Amazake and shio koji made with brown rice koji are also delicious with a deep flavor.

I hope you now have a better understanding of the difference between rice used for sake and miso. If you understand how it works, I hope you can apply what I have just explained to making koji with a medium other than rice, taking into account its intended purpose and use.

Rice paddy in Japan
Malica Ferments | + posts

Marika Groen is the head of Malica Ferments, an online platform dedicated to fermented products. As a Kojiologist, traveler, brewer, photographer, and writer, she published the book "Cosy Koji" in 2021, offering insights into the art of Koji making based on her worldwide lectures and experiences.