noun From Latin residuus ("remaining") — the sugar that remains after fermentation is complete or halted

Residual sugar /ˈrezɪdjuəl ˈʃʊɡə/

The natural grape sugars that remain in a wine after fermentation has ended, expressed in grams per litre (g/L). Residual sugar (RS) determines a wine's perceived sweetness, though the balance with acidity affects how sweet the wine actually tastes.

Sweetness levels by residual sugar

Style RS (g/L) Perception Examples

Bone dry 0–2 g/L No sweetness detectable Most red wines, dry Riesling (Trocken), Chablis, dry Champagne Brut Nature

Dry 2–9 g/L Imperceptibly sweet to most tasters Standard Champagne Brut, most table wines, Sauvignon Blanc

Off-dry 9–18 g/L Slight sweetness, especially on the finish Mosel Kabinett, Demi-Sec Champagne, many Gewurztraminer

Medium 18–45 g/L Clearly sweet but not dessert-level Mosel Spätlese, Demi-Sec Vouvray, Amontillado cream styles

Medium-sweet 45–120 g/L Noticeably sweet Mosel Auslese, Beerenauslese, Tokaji Aszú 3–4 Puttonyos

Sweet 120+ g/L Intensely sweet Sauternes, Trockenbeerenauslese, Eiswein, Pedro Ximénez Sherry

How residual sugar is created

All grape juice contains sugar — primarily glucose and fructose — at levels determined by the ripeness of the fruit at harvest. During fermentation, yeast converts this sugar into alcohol and CO₂. In a dry wine, fermentation runs to completion: virtually all sugar is converted and the yeast die from the accumulated alcohol. RS stays below 2–3 g/L, which is below most tasters' detection threshold.

Sweet wines arise when fermentation stops before all sugar is consumed. This can happen naturally (when alcohol levels rise high enough to kill the yeast before all sugar is converted, as in Port) or deliberately (when the winemaker chills the fermenting wine or adds sulphites to stop the yeast). High-sugar dessert wines made from botrytis-affected, dried or frozen grapes start with so much sugar that even a complete fermentation would leave substantial RS.

Sources: WSET (wine sweetness classification), OIV (sugar measurement standards and definitions), AWRI (residual sugar analytical methods), Deutsches Weininstitut (DWI) (German Prädikat system and sweetness levels).

Questions

About residual sugar.

Why doesn't a wine with 15 g/L residual sugar always taste sweet?

Sweetness perception is not determined by residual sugar alone — it is the ratio of sugar to acidity. A wine with 15 g/L RS and very high acidity (a Mosel Riesling Kabinett, for example) may taste more "fresh" than "sweet" because the acidity suppresses the sweetness perception. The same 15 g/L RS in a low-acid wine would taste noticeably sweet. This is why the Mosel classification — Kabinett, Spätlese, Auslese — refers to sugar at harvest rather than finished sweetness: a Kabinett at 8.5% ABV can be perceived as off-dry rather than sweet. See the acidity glossary entry for how acidity interacts with sugar balance.

How is residual sugar measured?

RS is typically measured by enzymatic analysis or by refractometry/density methods in a wine laboratory. At the winery, fermentation progress is tracked using a hydrometer or refractometer to measure Brix (dissolved solids, mostly sugar) in the fermenting must. When fermentation is complete or deliberately stopped, the residual Brix is converted to approximate g/L RS. Certified analytical results (required for export and labelling purposes in many markets) come from accredited wine laboratories.

Is residual sugar added to wine, or does it occur naturally?

Both. Natural RS is the unconverted grape sugar left when fermentation stops naturally (when yeast die from high alcohol levels) or when the winemaker arrests fermentation by chilling or by adding sulphites. In Champagne and most sparkling wine, the dosage (liqueur d'expédition) — a small addition of wine plus sugar added at disgorgement — contributes RS directly. In some cheap commercial wines, concentrated grape juice is sometimes added after fermentation to add sweetness. EU regulations require that any added sweetening must be from grape-derived sources. See the dosage glossary entry for how RS is managed in sparkling wine production.

Does residual sugar affect how long a wine lasts after opening?

Yes — sugar is a preservative at sufficient concentrations, and sweet wines last longer after opening than dry wines. A dessert wine like Sauternes or Beerenauslese can last a week or more after opening (refrigerated, recorked). A bone-dry white wine typically begins to deteriorate within 1–3 days. The alcohol level is also relevant: high-alcohol sweet wines (Tokaji, Pedro Ximénez Sherry, Port) last the longest. See the How long an open bottle lasts guide for style-by-style guidance.

What is a wine sweetness chart and how do I use one?

A wine sweetness chart ranks wines by their residual sugar content (g/L) from bone-dry to intensely sweet. The table on this page is such a chart: Bone dry (0–2 g/L) → Dry (2–9 g/L) → Off-dry (9–18 g/L) → Medium (18–45 g/L) → Medium-sweet (45–120 g/L) → Sweet (120+ g/L). Use it by matching a wine style you know to its RS level, then using that level to find similar alternatives. For example: if you enjoy Mosel Spätlese (off-dry, ~20–40 g/L), you might also enjoy a Demi-Sec Vouvray or a lightly sweet Gewurztraminer from Alsace. The key caveat: perceived sweetness also depends on acidity — a high-acid wine with moderate RS will taste less sweet than a low-acid wine with the same RS.

What are the sweetest wine styles?

The sweetest wines in the world include: Trockenbeerenauslese (TBA) — German Riesling from individually selected botrytis-affected dried berries (residual sugar 300–800 g/L); Eiswein — from grapes naturally frozen on the vine; Pedro Ximénez (PX) Sherry — sun-dried Palomino grapes, molasses-thick, 300–500 g/L RS; Sauternes — botrytis-affected Sémillon and Sauvignon Blanc from Bordeaux, 80–200 g/L RS; Hungarian Tokaji Aszú — up to 6 puttonyos (450 g/L RS). Commercial sweet wines like Moscato d'Asti (around 120 g/L RS) and sweet Riesling (Spätlese, Auslese) are more accessible. See the Sparkling sweetness terms guide for sweet sparkling wines specifically.

How do I know if a wine will be sweet from the label?

It depends on the country. German Riesling: look for "Trocken" (dry) or the absence of sweetness indication (Kabinett and Spätlese without Trocken are typically off-dry). Champagne: Brut Nature and Extra Brut are bone-dry; Brut is dry to off-dry; Extra Sec, Sec and Demi-Sec are progressively sweeter. Vouvray (Loire): Sec, Demi-Sec, Moelleux, Liquoreux. Bordeaux-style labels: wines labelled "Sauternes" or "Barsac" are always sweet. For a comprehensive guide to label sweetness terms, see the Sparkling sweetness terms guide and the How to read a wine label guide.