What happens to the sugar in grape juice during fermentation?

During fermentation, the sugar in grape juice is converted into alcohol and carbon dioxide through the action of yeast. This process begins when yeast cells consume the sugars present in the grape juice, primarily glucose and fructose, and convert them into ethanol (the alcohol in wine) and carbon dioxide as by-products. This transformation is crucial in winemaking as it not only creates the alcohol content of the wine but also contributes to the development of different flavors and aromas.

The production of carbon dioxide during fermentation is often visible as bubbles, which can be particularly noticeable in processes like sparkling wine production.

Understanding this transformation emphasizes the importance of sugar both as a vital ingredient in wine creation and as a key factor in determining the wine's final taste and alcohol level.