Chaptalization and enrichment: how much sugar, how much alcohol, and the limits

When a cool season leaves the grapes short of sugar, enrichment — chaptalization with sugar, or adding concentrated or rectified must — lifts the potential alcohol to a target. It is simple arithmetic, but it is tightly regulated and easy to overshoot. Here is how to size it and what limits to check.

The conversion factor

Yeast needs roughly 16–17 grams of sugar per litre to produce 1% vol of alcohol. The exact figure depends on the strain and fermentation conditions, but ~17 g/L per %vol is the working number for planning. To raise a 2,000 L tank by 1% vol you therefore need about 17 g/L × 2,000 L = 34 kg of pure sugar.

Rule of thumb: sugar to add (kg) = target increase (%vol) × 17 × volume (L) ÷ 1000. Always express the result as pure sugar first, then convert to product.

Sugar vs concentrated must

• Granulated sugar — nearly 100% fermentable sugar, no added volume worth counting. Cheapest and simplest where it is legal.
• Concentrated must / RCGM (rectified concentrated grape must) — a fraction of sugar (e.g. 65%) in a dense liquid, so you add real volume and must account for it. Preferred or mandatory in many appellations because it keeps the wine "all grape".
• Because concentrated must adds volume, the effective dilution slightly offsets the alcohol gain — the calculator handles this by working from pure sugar and the product’s sugar fraction and density.

Know the limits before you add

Enrichment is capped by regulation — in the EU, by wine-growing zone and vintage, with a maximum increase in potential alcohol and an absolute ceiling on the finished degree. Some appellations forbid it entirely. Adding sugar without checking is not a quality problem, it is a compliance one.

In GrapeFlow the enrichment is recorded against the lot alongside the initial must analysis, so the potential alcohol you started from and the correction you made travel with the wine.

Check your appellation’s current enrichment rules and limits before adding, and confirm the finished degree with analysis.