All wine is fermented, no matter if it’s made from grapes or other fruits. Fermentation is when yeasts eat and break down sugars. As a byproduct, they release alcohol. When winemakers add yeast to sweet grape juice, it takes around one to two weeks for the yeasts to turn the sugars in the juice into alcohol. 

Fermented wine usually has between 12% to 15% alcohol by volume. As a rule of thumb, the sweeter the grape, the more alcohol it can produce. 

The most common type of yeast to use for fermented wine is Saccharomyces cerevisiae. However, there are many wild yeasts that live on grape skins in the wild. Some winemakers use these yeast strains to make their wines. These are called ‘natural wines.’