Made from rice and water, sake is often called “rice wine” – however, it is brewed in a process closer to the preparation of beer rather than solely fermented like grapes for wine. Just as Italians and French use wine to add depth and flavor to many dishes, the Japanese use sake in the same way. And much like mirin (a higher sugar, lower alcohol version of sake), sake can round out the flavors of a dish and has the masking properties of making seafood small less “fishy”.
While there are many types of sake made for drinking and savoring on their own, a lower quality variation called ryorishi is used exclusively for cooking. Ryorishi sake has salt added, making it unfit to drink – and adds the benefit of allowing it to be sold as a cooking ingredient in shops not licensed to sell alcohol. But don’t think you have to use cooking sake in the kitchen exclusively. A decent to good drinking sake can really make a dish pop and add a subtle depth of flavor you might not get from cooking sake.