Cultured yeasts are industrially grown pure yeasts strains optimised for the vinification of the wine. There are many pure cultured yeasts (also known as wine yeasts) that all belong to the yeast species Saccharomyces cerevisiae. These cultured yeasts are selected for their optimal properties for wine making. They efficiently convert the sugar in the must into alcohol without the excess production of volatile acids or undesirable aromas. Inoculation of the must with an excess of cultured Saccharomyces cerevisae yeast strain prevents the growth of other (non-Saccharomyces) yeasts such as Kloeckera, Candida or Brettanomyces yeast strains. These yeasts, often referred to as ‘wild yeasts’, are also found on the grapes in the vineyard. They often produce more volatile acids and undesirable aromas than the Saccharomyces culture yeasts and are not always resistant to higher alcohol percentages and therefore not able to ferment all sugars in the must. This can cause the alcoholic fermentation to go too slow – which increases the risk of wine faults – or even stop. Although the use of cultured yeast is therefore a safer option, the vinification with the help of natural, wild yeasts often results in a much more complex wine. There are therefore a large number of wineries that go for the less secure option and make wines with the yeasts that are naturally present in the vineyard and wine cellar.