What does Residual sugar mean?

Residual sugar is the grape sugar left in the wine after fermentation, in grams per litre; up to 4 g/l a wine counts as dry.

Also known as: Sugar content, RS

Residual sugar is the grape sugar still left in the wine once fermentation has finished. It is given in grams per litre (g/l) and is a measured value, unlike sweetness, which describes how the wine actually tastes.

During fermentation yeast converts sugar into alcohol and carbon dioxide. If the wine ferments fully, residual sugar ends up very low, often 1 to 3 g/l. The producer can also stop fermentation by chilling, filtering or, in fortified wine, adding grape spirit, which leaves more sugar behind.

EU rules for still wine allow a dry wine up to 4 g/l, or up to 9 g/l if total acidity is no more than 2 g/l below the sugar level. Medium dry goes up to 12 g/l (18 g/l if total acidity is no more than 10 g/l below the sugar), medium sweet up to 45 g/l, and sweet is anything above. Sparkling wine has its own scale, from brut nature to doux.

In the glass, acidity shapes the impression a great deal. A riesling with 8 g/l of sugar and high acidity can taste almost dry, while the same sugar in a low-acid wine is clearly noticeable. That is why the wine page shows residual sugar as an exact figure next to acidity and sweetness.