Wine · Terminology
Residual sugar
The grape sugar left unfermented in the finished wine — what makes it taste sweet.
Residual sugar — RS — is the grape sugar still in the wine when fermentation ends. Yeast converts sugar into alcohol and carbon dioxide; whatever it does not get through stays behind and tastes sweet.
Sugar survives for one of two reasons: the yeast ran out of road (it died of alcohol, cold or nutrient exhaustion), or the winemaker stopped it on purpose — by chilling, filtering, adding sulfur dioxide, or fortifying with spirit. Sweetness can also be added back after the fact, as with the dosage in sparkling wine.
In practice
- Measured in grams per litre. Roughly: under 4 g/L dry, 4–12 g/L off-dry, 12–45 g/L medium, above 45 g/L sweet.
- Acidity changes the perception entirely. A Mosel Kabinett with 40 g/L can taste fresher than a flabby dry white with 6 g/L.
- Sugar adds body and viscosity as well as sweetness — the reason sweet wines look thick in the glass and throw heavy legs.
- Most everyday commercial wines carry a few grams of RS whether or not they taste sweet.
Where you'll meet it
- German Prädikatswein, where the ripeness ladder from Kabinett up to Trockenbeerenauslese is really a sugar ladder.
- Sparkling wine labels: Brut Nature through to Doux.
- Botrytis and late harvest sweet wines everywhere.
The dryness scale
| Label term | Typical RS | Example |
|---|---|---|
| Bone dry / Brut Nature | 0–3 g/L | Zero-dosage Champagne |
| Dry / Brut | 3–12 g/L | Most still whites and reds; Brut Champagne |
| Off-dry | 12–35 g/L | Kabinett, many Vouvray demi-sec |
| Medium sweet | 35–120 g/L | Auslese, Sauternes at the lighter end |
| Luscious | 120 g/L + | Trockenbeerenauslese, Tokaji Aszú, PX Sherry |
The bands overlap by design: legal definitions differ by country and by category, and sparkling wine has its own scale entirely.
The exam angle
- Report sweetness as perceived, not as measured — the tasting note asks what the wine tastes like.
- Always tie the judgement to acidity: "medium sweet, but high acidity keeps it balanced and fresh" is the sentence that scores.
- Know the causes, because production questions ask for them: arrested fermentation, fortification, concentration by noble rot or freezing, or the addition of sweet reserve.
Related terms
- Fermentation — what leaves the sugar behind
- Fortification — killing the yeast with spirit
- Dosage — sweetness added after disgorgement
- Acidity — the counterweight