Residual Sugar (RS)
The amount of sugar remaining in wine after fermentation is complete, measured in grams per litre (g/L). It determines the wine's sweetness from bone dry to lusciously sweet.
In depth
During fermentation, yeast convert grape sugars (glucose and fructose) into alcohol and CO₂. If fermentation runs to completion, virtually all sugar is converted and the wine is dry. Residual sugar remains when fermentation is stopped early (by chilling, adding alcohol, or filtering out yeast), or when grapes contain so much sugar that the yeast are killed by the rising alcohol before all sugar is consumed.
Typical residual sugar levels: Dry wine: 0–4 g/L (below the human perception threshold of about 5–6 g/L). Off-dry: 5–12 g/L. Medium: 12–45 g/L. Medium-sweet: 45–120 g/L. Sweet/dessert: 120+ g/L. German Trockenbeerenauslese can exceed 300 g/L.
RS alone does not determine how sweet a wine tastes — perceived sweetness depends on the balance with acidity. A wine with 40 g/L RS and very high acidity (like a German Spätlese) may taste only off-dry because the acid counterbalances the sweetness. A wine with 15 g/L RS and low acidity may taste noticeably sweet.
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Frequently asked questions
- Can a wine taste dry even if it has residual sugar?
- Yes. Perceived sweetness depends on the balance between sugar and acidity. A German Kabinett Riesling may have 15–20 g/L RS but taste almost dry because its very high acidity counteracts the sweetness. Conversely, a wine with only 8 g/L RS but low acidity may taste noticeably sweet. This is why the systematic tasting framework assesses sweetness as a perceived sensation, not just a measurement.
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