One of the six officially recognized taste sensations (besides bitter, oily, salty, sour, umami), which is perceived at the tip of the tongue. The sweet taste of a wine is perceived mainly because of the residual sugar; this is the amount of unfermented sugar in g/l. With a sparkling wine, the taste sensation for "sweet" is different, as the carbonic acid reduces the sweetness quite significantly. However, the subjective taste perception for sweetness depends on many factors. Among other things, it depends on the relationship of the various ingredients to each other. Therefore the taste impression does not have to be identical with the actual analysis values. The opposite of sweet is sour in taste. However, this does not apply in the chemical sense, because in this respect alkaline is the opposite of sour.
Wines with a low residual sugar content can certainly be perceived as sweet when the acidity is low, whereas wines with a high residual sugar and acid content appear dry. Likewise, high contents of alcohol and glycerine lead to the impression of sweet, although the wine is actually dry according to analysis values. The age of the wine also plays a role, as certain substances polymerise during bottle ageing. As a result, noble sweet wines can taste less sweet in old age than when they were young, and old, dry red wines appear sweetish due to milder tannins. Finally, the wine temperature also has an influence. The same amount of sugar appears significantly sweeter at 18 °Celsius than at 10 °Celsius.
According to the EU regulation, the indication of taste "sweet" can optionally appear on the bottle label (however, according to Austrian wine law, labelling is obligatory). The degree of sweetness and the designation are prescribed by wine law for each wine type: a sweet still wine must have at least 45 g/l, a mild (equivalent to sweet) sparkling wine more than 50 g/l residual sugar. For the other flavours, see a table under sugar content.
From the 1990s onwards, there was and still is a worldwide trend towards dry wines. Sweet wines, however, are still among the specialities that are mainly enjoyed as a dessert wine or as the conclusion of several courses. Top products are for example Banyuls, Château d'Yquem, Tokajer and Vin Santo. The designations for sweet wines regulated by wine law in Germany and Austria, but also in other countries, are the predicate levels Auslese, Beerenauslese, Strohwein (also reed wine), Ausbruch (is reserved for a wine from the Burgenland community of Rust) or Trockenbeerenauslese and Eiswein. In principle, however, any wine can be made sweet.