How to make Koji at home

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Equipment

Don’t rinse the rice or barley. You want the extra starch to stay around. Koji consumes starch—more is better for the fungus.
Cook the rice or barley. You want it to be fluffy and the grains to maintain their shape.
Cool the cooked rice or barley to 90°.
Sprinkle the koji spores once the grain is cooled. Gently toss so that the spores are evenly dispersed.
Set your dehydrator to between 80° and 90°. Place the grain and spore mixture on the dehydrator trays.
Cover each tray with thick layers of cheesecloth or plastic wrap. If using plastic wrap, be sure to poke holes in it or to leave the edges of the pan open to allow for air circulation. Insert the trays into the dehydrator.
Using clean hands, gently mix the inoculated grain a few times a day over the next 48-72 hours. After 2-3 days, you’ll have your koji. The rice or barley will have a fuzzy white covering and have an extremely yeasty and sweet floral aroma. At this point, you can dry the koji and freeze it.
You can also turn it into Amazake, which is sweet koji, or Shio, which is salt koji.

Make a thin rice porridge by cooking the rice in the water, which may take about 30 minutes. The porridge is ready when it resembles a thin rice pudding and the grains of rice have completely broken apart.
Once the porridge is cooked, let it cool down to 80° for sour Amazake or 138° for sweet Amazake. Add the koji rice.
Keep the mixture at the desired temperature for 6-10 hours or overnight. The Amazake is finished after incubating. Cool it down, and store it in an airtight container in the fridge.

Mix all the ingredients evenly together.
Transfer the ingredients to a glass bowl. Leave the bowl on your counter, covered.
Mix the ingredients 1-2 times a day for 7 days. After seven days, your Shio-koji is ready. Store it in an airtight container in your fridge.