The sweetness of a wine is defined by the level of residual sugar (or RS) in the final liquid after the fermentation has ceased. However, how sweet the wine will actually taste is also controlled by factors such as the acidity and alcohol levels, the amount of tannin present, and whether the wine is sparkling. For example, a sweet wine such as a Vouvray can actually taste dry due to the high level of acidity, or a dry wine can taste sweet if the alcohol level is elevated.

In recent decades, an increase in the population who only occasionally drink wine has led to an increase in the sweetness of many cheap wines, and as a result medium and sweet wines have a perception among many drinkers of being of lower quality than dry wines. However, many of the world's great wines, such as those from Sauternes, Barsac or Tokaj, have a high level of residual sugar which is carefully balanced with additional acidity to produce a harmonious result.

Terms used to indicate sweetness of wine

The principal wine-producing countries of Europe use different terms to indicate the rough level of residual sugar, which is usually measured in grams per liter (as in the table below).

The region of Tokaj-Hegyalja in Hungary has a more graduated terminology to describe Tokaji Aszú dessert wines: