Dry white and red wines have just a trace amount of sugar in them; they contain less than one gram per glass. As wines become less dry, they contain more sugar.
The amount of natural sugar in grapes varies. Grapes from warm climates tend to contain more sugar than those from cooler climes. Red grapes typically have more sugar compared to white varieties. When wine is made, yeast turns much of the grape's natural sugar into alcohol. Some sugar is left over. This "residual" sugar gives wine its level of sweetness. Dry wines have the lowest sugar content. A sweet wine has about 5 grams of sugar in each serving.