The subjective
sweetness of a
wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of
alcohol, acids, and
tannins. Briefly: sugars and alcohol enhance a wine's sweetness; acids (sourness) and bitter tannins counteract it. These principles are outlined in the classic 1987 work by
Émile Peynaud,
The Taste of Wine.