Residual Sugar

Definition - What does Residual Sugar mean?

Residual Sugar is the sugar that remains in a wine after fermentation completes. It usually remains for one of three reasons:

  1. The yeast was unable to continue converting sugar to alcohol
  2. The wine was fortified with a hard alcohol, which stopped fermentation
  3. The temperature dropped significantly, killing the yeast

Residual sugar is balanced by acidity, alcohol and tannins in wine. It is measured in grams per liter (g/L). Winemakers usually test during fermentation using either the Brix Hydrometer or Clinitest. These methods allow them to track the progress of the yeast and decide if fermentation should be stopped manually or allowed to cease naturally.

WineFrog explains Residual Sugar

Residual sugar, though it has an impact on the characteristics of the wine, is usually not the basis of determining the sweetness. That being said, the g/L can be a starting point for the consumer. The average red table wine has less than 1 g/L of residual sugar. The average white wine has between 4 and 45 g/L. In order for a wine to be considered truly sweet (think dessert wine), it has to have over 45 g/L.

Winemakers balance the residual sugar with acidity, alcohol, acids and tannins. It can be used to ensure a wine ages well, always evolving into a complex and interesting wine. The sugar compounds change shape as wine ages, which means we "perceive" them less directly and in new ways with every year that passes. Some winemakers also use residual sugar to emphasize the fruit characteristics of their red wines. It also serves to hid strong, stringy and unwanted tannins.

As with any good thing, an overabundance of residual sugar - if not planned for - can cause destabilization of the wine as it ages and possible refermentation. This occurs when the sugar particles interact with the remaining yeast and alcohol particles in a wine.

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