Shio koji step by step
Koji (such as Cold Mountain brand) can be purchased at select Japanese markets such as Nijiya, Marukai and Mitsuwa.
Place 1 1/2 cups (200 grams) koji in a medium nonreactive bowl or container and add 4 2/3 tablespoons (70 grams) sea salt. Mix thoroughly and vigorously, using your hands.
Heat 1 1/4 cup water to 140 degrees and add just enough of the water to moisten the mixture. Knead until fragrant, about 1 minute. Then mix in the remaining hot water.
Store, covered loosely, at room temperature for one week. Stir once a day, making sure to aerate the mixture from the bottom.
The shio koji will take 7 to 10 days to reach full flavor. When ready, the koji rice grains will be smaller in size and the mixture will smell salty-sweet and have the consistency of loose porridge. Keep refrigerated and covered for up to 6 months.