After crushing and pressing, fermentation comes into play. Must (or juice) can begin fermenting naturally within 6-12 hours when aided with wild yeasts in the air. However, many wine makers intervene and add a commercial cultured yeast to ensure consistency and predict the end result.
Fermentation continues until all of the sugar is converted into alcohol and dry wine is produced. To create a sweet wine, wine makers will sometimes stop the process before all of the sugar is converted. Fermentation can take anywhere from 10 days to one month or more.