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. 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. Even among the driest wines, it is rare to find wines with a level of less than 1 g/L, due to the unfermentability of certain types of sugars, such as
pentose. By contrast, any wine with over 45 g/L would be considered sweet, though many of the great sweet wines have levels much higher than this. For example, the great
vintages of
Château d'Yquem contain between 100 and 150 g/L of residual sugar. The sweetest form of the
Tokaji, the Eszencia, contains over 450 g/L, with exceptional vintages registering 900 g/L. Such wines are balanced, keeping them from becoming cloyingly sweet, by carefully developed use of
acidity. This means that the finest sweet wines are made with
grape varieties that keep their acidity even at very high
ripeness levels, such as
Riesling and
Chenin blanc. 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 sweet wine such as a
Vouvray can actually taste dry due to the high level of acidity. A dry wine can taste sweet if the alcohol level is elevated. Medium and sweet wines have a perception among many consumers of being of lower quality than dry wines. However, many of the world's great wines, such as those from
Sauternes (including
Barsac) or
Tokaj, have a high level of residual sugar, which is carefully balanced with additional acidity to produce a harmonious result. == Süssreserve ==