I regularly visit a winery whose red wine reaches very high alcohol percentages, sometimes more than 16 °.
It also happens that residual sugar can be tasted in the wine so that I suspect that “somewhere” the fermentation stops because there is too much alcohol.
(For example, porto, the fermentation is also stopped by the addition of alcohol)
Answer
Alcohol is not harmless to the yeast that produces the alcohol. It is for this reason that the yeast excretes the alcohol into the surrounding liquid. The yeast can tolerate a certain percentage of alcohol, but at an alcohol percentage of around 15% it is over. Then the amount of alcohol is so large that it becomes toxic to the yeast, with the result that the yeast stops. And if you had grapes that had a particularly high sugar content due to the abundant sun, you may still have residual sugars at that high alcohol percentage of 15 or 16%. In other cases where the amount of sugars in the grapes are limited, the yeast stops (for example at an alcohol content of 12%) because the sugars are gone. The fermentation can therefore stop spontaneously for two reasons: because the sugars have run out, or because the alcohol percentage has risen so high that it is toxic to the yeast.
Answered by
ir Rene Custers
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