Wine is made from grapes. The crucial process in winemaking is fermentation, where yeast converts the sugar from the grapes into alcohol and carbon dioxide. After the harvest, the ripe grapes are first lightly crushed. This produces the mash: the mixture of juice, pulp, skins and seeds. The juice is then fermented in stainless steel tanks or oak barrels. During fermentation, yeast consumes the sugar in the juice and converts it into alcohol and carbon dioxide. The wine is then aged in oak barrels or stainless steel tanks for several months to several years depending on the type of wine.