Looking at how wine, beer and sake are brewed should make it more clear just what sake is. Wine is a fermented beverage. Fermentation is the process in which yeast converts sugar to alcohol and carbon dioxide, which in the case of wine, is allowed to escape. Sugars are already present in the grape, and these sugars are ready for use by the yeast cells as food and nutrients. Although this simple and short explanation does not do justice to the age-old art of making wine, it will serve our purposes here.
Beer calls for another step.
There is no fermentable sugar in barley grains, only long starch molecules that must be broken down into smaller sugar molecules, some that will ferment and some that will add to the flavor in other ways. To accomplish this, several other steps are necessary. First, the barley must be malted. The grains are moistened and warmed to start the germination process. This creates enzymes that patiently wait in the grain for their opportunity to create sugar from starch.