By natural yeasts (also natural yeasts, environmental yeasts, wild yeasts, grape yeasts, vineyard-owned yeasts) caused spontaneously fermentation in the winemaking, Until the middle of the 19th century, yeasts were unknown as polluters and were first introduced by Louis Pasteur (1822-1895) proved. Until the 1970s, the wines were usually the product of a spontaneous fermentation. The natural yeasts are to a greater extent in the air in the vineyard and are used by insects like vinegar flies (Fruit flies) spread. These then reach the cellar with the grapes. But they are not only from the vineyard, but also from the cellar of the area around the farm. The amount is enough to make a spontaneous fermentation trigger.
In recent years, this form of winemaking is associated with the Terroir-thoughts become popular again. For the promotion also the rape and lees (Pressed and yeast residues) for one fertilization used in the vineyard to promote the targeted emergence of certain and vineyard's natural yeasts. Spontaneous fermentation can produce excellent but also undesirable results as it is much more difficult to control than with farmed yeasts. There are a number of wild yeasts, which actually "prevail" in fermentation, are more or less left to chance. Some of the yeast species finish already at 4% vol alcohol content their activity, whereby the risk of sticking of the fermentation consists. Wild yeasts can also cause unpleasant metabolites.
The fermentation is today predominantly targeted by specific or suitable for each type of wine culture yeasts (pure culture yeast) initiated to ensure the best possible fermentation process. The fact is, however, that yeasts of the species Saccharomyces (pure-breeding yeasts) are also involved in spontaneous fermentation, since these are also present in the vineyard and in the cellar environment. And even with a controlled fermentation with breeding yeasts, natural yeasts are involved, especially at the beginning, and this can hardly be prevented. An equally practiced form is to let fermentation begin with natural yeasts and later add yeasts that then "take command". Prolonged fermentation is rather difficult with cool fermentation temperatures, very sugar-rich musts, musk from fermented grape material, pasteurized musts and during a seepage.
In red wine preparation, much more vineyard yeast enters the mash. This means that compared to the white wine production also by means of natural yeasts a good fermentation process is easier (durchgegorene, dry wines). The wines from spontaneous fermentation are often characterized by more glycerin and higher quality alcohols, and possibly more volatile acids and higher residual sugar out. But you can not say that such wines have a better quality in principle. Finally, it should be noted that the term "spontaneous fermentation" (or similar) has no legal meaning. In practice, it is used quite flexibly. If a small batch of must is spontaneously fermented and the resulting yeast is used for the remainder of the must, it is, so to speak, an "in-house breeding yeast".
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