The role of yeast in winemaking is the most important element that distinguishes wine from fruit juice. In the absence of oxygen, yeast converts the sugars of the fruit into alcohol and carbon dioxide through the process of fermentation. The more sugars in the grapes, the higher the potential alcohol level of the wine if the yeast are allowed to carry out fermentation to dryness. Sometimes winemakers will stop fermentation early in order to leave some residual sugars and sweetness in the wine such as with dessert wines. This can be achieved by dropping fermentation temperatures to the point where the yeast are inactive, sterile filtering the wine to remove the yeast or fortification with brandy or neutral spirits to kill off the yeast cells. If fermentation is unintentionally stopped, such as when the yeasts become exhausted of available nutrients and the wine has not yet reached dryness, this is considered a stuck fermentation.
The process of fermentation at work on Pinot noir. As yeast consume the sugar in the must it releases alcohol and carbon dioxide (seen here as the foaming bubbles) as byproducts.
French scientist Louis Pasteur discovered the connection between microscopic yeast and the process of fermentation.
If a Chardonnay has too much "buttery" diacetyl notes, winemakers may add fresh yeast to the wine to consume the diacetyl and reduce it to the more neutral-smelling fusel oil 2,3-Butanediol.
The distinctive "aldehydic" notes of Sherry wines are caused by special yeast native to the Jerez wine region.
Wine is an alcoholic drink made from fermented fruit. Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made from grapes, and the term "wine" generally refers to grape wine when used without any qualification. Even so, wine can be made from a variety of fruit crops, including plum, cherry, pomegranate, blueberry, currant, and elderberry.
Glasses of red and white wine
Georgian clay vessels, historically used in wine making.
The Areni-1 cave in Armenia is home to the world's oldest known winery.
Pressing wine after the harvest; Tacuinum Sanitatis, 14th century