Sugar is necessary for winemaking. During the process of fermentation, the sugar molecules in grapes are converted to alcohol and carbon dioxide by yeast.
The primary sugars in grapes are glucose and fructose. There are other sugars present, but are in lesser quantities. In some cases sugar is added to the grapes, known as chaptalization, to increase the alcohol content.
Grape maturity at harvest is critical for fermentation and perceptible sweetness. The Brix scale was developed to monitor sugar development and concentration. Brix readings give objective numbers that are used to determine the appropriate time for harvest.
Currently, there are no regulations in the United States regarding labeling the sugar content of wines, so for exact information about the nutritional content of your wine, you should check with the winery.
In general, most red wines have little sugar; most sweet wines are white. Key terms on the wine label can help you determine how sweet a wine will be. The term "dry" indicates a wine with less sugar. The small amount of residual sugar plays a role in balance and mouth-feel of wine.
Balance in wine is determined by the interplay of sugar, alcohol and fruit (the sweet components) with the acid and tannin (the tart components). Most red wines are balanced by the fruit and alcohol component versus the tannin and acid. White wine contains little tannin so are typically more acidic than reds. White wine generally has less alcohol than red so sugar commonly plays a balancing role to the acid.
