🍷 Residual sugar

Residual sugar is the grape sugar left in a wine after fermentation. During fermentation, yeast turns the sugar in the juice into alcohol and carbon dioxide. If it eats almost all of it, the wine is dry. If fermentation stops earlier, the wine stays sweet.

Fermentation can be stopped by chilling, filtering or adding spirit, as in fortified wines. Sometimes the yeast stops on its own when there is a lot of alcohol and the juice was very rich in sugar.

Sugar is measured in grams per litre. Dry wine usually has 0–4 g/l, medium dry up to 12, medium sweet up to 45, and sweet over 45 g/l. Tokaji Eszencia can have 400 g/l or more. These limits come from EU labelling rules.

The sugar left behind is mostly fructose, because yeast prefers glucose. Perceived sweetness also depends on acidity: a tart wine tastes less sweet. This is how dry wine and sweet wine are linked.