What does yeast eat?
Yeast is a one-cell fungi organism. It is widely used in baking wheat-based foods like bread, but is also used to make beer, wine and certain cheeses. When a yeast organism consumes sugar, the byproducts include carbon dioxide and alcohols. Many alcoholic drinks are created from this process, which is called fermentation. Wine is simply the fermentation of a fruit, typically grapes. The produced carbon dioxide can make baking goods “rise,” which is why yeast is used in breads. Source: howstuffworks.com