The sweetness of a wine is defined by the level of residual sugar in the final wine after the fermentation process 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. A sweet wine can actually taste dry due to the high level of acidity, or a dry wine can taste sweet if the alcohol level is elevated.
Young wines taste sweeter than aged wines. The powerful bouquet of fruit in young wines causes your sense of smell to overpower your sense of taste, and tricks your senses to believe the wine tastes sweeter than it is. People who don’t like the dry tannic taste of heavily oaked red wines often like the taste of lightly oaked young red wine.
Several methods have been used throughout history to sweeten wine. The most common way to sweeten wine was to harvest the grapes as late as possible. This method is used today to create “ice wines”, and was first advocated in Roman times. Early Greeks would harvest the grapes early, to preserve some of their acidity, and then leave the grapes in the sun for a few days to shrivel and concentrate the sugars.
Stopping the fermentation early also enhances a wine’s potential sweetness, but is very difficult to do. Wine can also be sweetened by the addition of sugar in some form after the fermentation has completed.