Japanese koji tray incubator

What it is

A koji tray incubator is an insulated cabinet holding shallow, food-safe trays of steamed grain that have been inoculated with a commercial koji culture. The brief specifies controllable heat, humidity that does not spray the grain, and a way to remove heat. Shallow trays keep the grain bed thin enough to stay aerated and to be mixed by hand.

The grain bed should be measured separately from the room air, because the mould generates heat as it grows.

Conditions

Home koji guides report about 28 to 32 C and 70 to 80 per cent humidity, and the figures in the sources conflict. A university study reported success at 25 C and 70 per cent humidity, and at 27 C and 80 per cent, on steamed barley. The settings depend on the strain and the substrate, so the page gives no fixed setting.

Controlled koji incubation with a microcomputer has been applied to barley koji, which shows that the principle of a timed, controlled incubator is established in the literature.

Related build

Japanese koji making has also used underground chambers, called muro, which hold humidity and temperature through the earth around them. Those are builds rather than equipment, and this tray incubator is the portable counterpart for a home kitchen.