Crumble the dehydrated koji sheets into a plastic container with a lid. Mix in the coarse salt. Add enough water to cover the koji, and mix well.
The dehydrated koji absorbs a lot of water, so check on it after a few hours. If it has swelled and absorbed all the moisture, add a little more water.
Cover with the container lid, and leave out at room temperature for 5 to 7 days. Mix it up well with a spoon at least once a day.
When the koji grains have broken down, become creamy, and smells like fermented koji with a nice light brown color, it means the shio-koji has matured. Transfer the container to the refrigerator.
I made chicken ham with shio-koji. It comes out tender and moist. You can use this for all kinds of dishes.
Story Behind this Recipe
Shio-koji is an all-purpose flavoring ingredient with a mild saltiness and the umami of malted rice that makes any ingredient delicious. We don't buy it - we always make it at home.
You can make shio-koji easily without having to fuss over it too much. I recommend using koji with visible spore threads. Shio-koji is especially suited for marinating salmon and chicken. You can also marinate vegetables with it, make dressings, sauces, and using in stir fries.