How to Make Koji 3: Preparing Your Substrate

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.

If you have read my previous articles, you are almost ready to try making your koji! The rest of the items are rather easy to obtain, so let’s get them as we go together. In this article, I talk about how to prepare your substrate. Let’s say you find your ideal rice. The first thing to do is to rinse it. By washing the rice thoroughly, the bran on the surface is cleaned off. Wash the rice by hand while changing the water several times, and when the water becomes less cloudy, rinsing is done.

Once the rice is washed, then you steep it in a plenty of water overnight. How many hours precisely? This depends on the type of rice and temperature of water (generally cold water is preferred as warm water may make the rice grain crack when draining). The good news is that you can always check the hydration by your fingers. Japanese koji making is full of this kind of classic tips that only requires your body.

Pick up several grains from the water. Wipe off the surface and squish the grains between your fingertips. Did it turn into rice flour? Then the rice is hydrated enough. If it does not turn into flour and fine bead-like particles remain on the fingertips, extend the soaking time. This way of checking the hydration is called “kashi” check.