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 alcohols, acids, and tannins. Sugars and alcohol enhance a wine's sweetness; acids (sourness) and bitter tannins counteract it.
Among the components influencing how sweet a wine will taste is residual sugar. It is usually measured in grams of sugar per litre of wine, often abbreviated to g/l or g/L or in %. 1% sweetness is equal to 10 g/L residual sugar (RS).
Residual sugar typically refers to the sugar remaining after fermentation stops, or is stopped, but it can also result from the addition of unfermented must (a technique practiced in Germany and known as Süssreserve) or ordinary table sugar.
  • Below 1% sweetness, wines are considered dry.
  • Above 3% sweetness, wines taste “off-dry,” or semi-sweet.
  • Wines above 5% sweetness are noticeably sweet!
  • Dessert wines start at around 7–9% sweetness.

How sweet a wine will taste is also controlled by factors such as the acidity and alcohol levels, the amount of tannin present, and whether the wine is sparkling or not. A technically sweet wine such can actually taste dry due to a high level of acidity and a dry wine can taste sweet if the alcohol level is elevated.

Some of the world's greatest sweet wines also have extremely high levels of acidity to counterbalance the sugar.

Again it’s all about that important balance.

For sparkling wines, we use terms as brut, brut nature, etc., so here is a small overview of what that actually means in terms of RS.

Rating Sugar content
(grams per litre)
Brut Nature (no added sugar) 0–3
Extra Brut 0–6
Brut 0–12
Extra Dry, Extra Sec, Extra seco 12–17
Dry, Sec, Seco 17–32
Demi-sec, Semi-seco 32–50
Doux, Sweet, Dulce 50+