1, the duration of main fermentation is usually about 7 to 15 days, which is mainly related to grape varieties, fermentation temperature and added sugar, but we can judge whether the main fermentation is terminated by tasting the newly brewed wine liquid. If you can smell a strong alcohol smell, but you can't feel the sweetness, it means that most of the sugar in the grape juice has been converted into alcohol, and the main fermentation process has ended.
2. Slow fermentation is carried out after the main fermentation stage. At this time, the longer it is left, the more mellow the wine will be, usually one month is the best.
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The principle of wine brewing is expressed by the equation:
Sugar+yeast = alcohol+carbon dioxide, that is, sugar is converted into alcohol and carbon dioxide under the action of yeast, and all alcoholic beverages are fermented by this principle.