Rice for Koji vs. Rice for Sake and Miso

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.

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.