Using Dried Koji

The Simple Part:

• Prepare any other ingredients that you are using, like salt, warm water, or cooked beans. Clean and prepare any vessels like jars that you will need later.

• Prepare 200 mL of warm water for every 500 grams of dried koji that you are going to use. It is best to boil the water, and then let it cool to around 50°C. Do not directly add boiling water to koji, or you will denature the enzymes.

• Soak the koji in the water for about an hour, until it is plump and soft. You can mix it if it makes you feel better.

• Use the rehydrated koji as you would fresh koji in any recipe that calls for it.

Why It Works:

Koji is a bit different than other ferments you might have tried at home. Koji is a fungus that produces an array of enzymes suitable for breaking down starch and protein. When correctly grown on a source of starch like steamed rice, the fungus spreads over the surface of the grain and into the interior. It begins to break down the starch into sugar, and prepares to use the energy to make spores.

Unfortunately for the koji, that is the point where it is harvested and used to make food or drinks; before it can produce the unpalatable spores. When you use koji to ferment food, the fungus is dead or dormant, but the enzymes it produced are still present and can be used to create a secondary ferment. For example unlocking nutrients for yeast, by breaking down starch into sugar.

When koji is dehydrated, the enzymes are quite stable; after water is added they immediately get to work, and begin breaking down protein and starch again. However, the koji mold should not begin to regrow, because it is inhibited by the liquid or salt.