Keyword: Spontaneous fermentation
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Without the influence of the winemaker by natural Yeasts (natural yeasts, environmental yeasts, wild yeasts) caused spontaneous onset of fermentation in the Winemaking . The so-called natural yeasts are to a greater extent in the air in the vineyard and are used by insects such as Vinegar fly (Fruit flies) spread. This takes you to the grapes in the cellar. But they must not only come from the vineyard, but can also in the basement of the farm's vicinity. The amount is sufficient to provide a fermentation trigger and earlier this was also the commonly used form. Not a few winemakers swear to this day and make it out even marketing point.
Often the proponents of this technique, the winery's own Marc and Lee (Press and yeast residues) for fertilization in the vineyard used to promote the emergence of certain specific vineyard and his own natural yeasts. The spontaneous fermentation, excellent, but also bring undesirable results, since it is much harder to control than with yeasts. There are a number of wild yeasts, which of these "assert" themselves during fermentation in fact, is more or less left to chance. Some of the yeast species terminate namely already at 4 vol% Alcohol content their activities, thereby reducing the risk of getting stuck fermentation is. Wild yeasts can also cause unpleasant metabolites.
The fermentation process is now largely determined by culture yeasts (yeasts) introduced deliberately in order to ensure the most satisfactory course of fermentation. But the fact is that even with a spontaneous fermentation yeasts of the Saccharomyces species (yeasts) are involved, since these are also in the vineyards and cellars in the area. And even in a controlled fermentation with selected yeasts are specifically involved in the early natural yeasts, this can hardly be prevented. A well practiced form to let start the fermentation with natural yeasts and yeast culture later add that "take command" then. More difficult is a spontaneous fermentation at cool fermentation temperatures, very high sugar musts, grape musts from gefaultem material, pasteurized cider and sparkling wine at a.
For the red wine-making with the skins get a lot more vineyard yeasts in the mash. This means that light over the white wine and using natural yeast fermentation process is a good possible (durchgegorene, dry wines). The spontaneous fermentation of wines are often characterized by more glycerol and higher alcohols, and possibly more volatile acids and a higher residual sugar from. But you can not say that these wines have in principle a better quality. Finally, it should be noted that the term "spontaneous fermentation" (or similar) has no legal significance wine. In practice it is used quite flexibly. When a small batch must is fermented spontaneously and the resulting yeast is used for the rest of the must, is to say at an "in-house Zuchthefe".