Residual sugar (RS) is the amount of fermentable and non-fermentable sugar remaining in wine after fermentation, usually expressed in grams per litre (g/L). It is a major factor in perceived sweetness, but the wine’s acidity, alcohol, tannin and flavour concentration also influence how sweet it tastes. A wine can contain some residual sugar and still taste dry.
During alcoholic fermentation, yeast converts grape sugars into ethanol and carbon dioxide. If fermentation is stopped before all the sugar is consumed, or if the grapes contain more sugar than the yeast can ferment under the chosen conditions, residual sugar remains. Producers may also use permitted methods such as sterile filtration, cooling or fortification to manage fermentation and sweetness.
Terms such as dry, off-dry, medium-sweet and sweet are used to describe wine styles, but the exact legal thresholds vary by wine category and jurisdiction. In the European Union, for example, the threshold for “dry” depends partly on total acidity; it is not one universal number for every wine. Sparkling-wine sweetness categories have their own defined limits.
High acidity can make a wine with noticeable residual sugar taste fresher and less sweet. Alcohol and fruit concentration can also affect perception. A dry wine may smell of ripe fruit without containing significant residual sugar, while a sweet wine with high acidity can feel balanced rather than cloying.
Example: an off-dry Riesling may have noticeable residual sugar balanced by high acidity, while a dry Sauvignon Blanc may show ripe tropical-fruit aromas but little perceptible sweetness.
Chef’s note: check residual sugar and acidity when pairing wine with dessert or spicy food. Do not assume that fruit-forward aromas mean the wine is sweet.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
