Yeast is an eukaryotic single-celled organism. Yeasts convert sugar into alcohol and carbon dioxide (CO2). This process is known as fermentation, and is used for the production of wine from must. Cultured yeasts from the yeast species Saccharomyces cerevisiae are most often used for the alcoholic fermentation during vinification. Nevertheless, there are many ‘wild yeasts’ that occur naturally on the grapes and that can also be used in the process of wine making.