Sake is a Japanese rice wine that is made during a brewing process by fermenting rice, during which the starches are converted into sugar, and then alcohol. The alcohol content of sake generally ranges from 14% to 16%, with the exception of the "genshu" variety of sake which has a higher alcohol content of 18% to 20%.
There are eight legally defined grades of premium sake. An important factor in deciding the grade of sake is the milling ratio of the rice, known as seimaibuai (精米歩合). This is a number you will see on every bottle of premium sake, indicating the remaining portion of the rice kernel after it is milled during production.