Shio koji is a salty Japanese seasoning made from koji, water and salt. Enzymes from the rice koji contribute sweetness and savory flavor and can soften the texture of proteins during marinating. It is used in dressings, vegetable dishes and marinades.
Because it supplies salt and can promote browning, reduce other salt and watch cooking heat. It is different from dry koji rice and from miso; use a recipe designed for the particular product.
Reference: Further reading.