Must weight explained: Brix, Baumé, Oechsle and potential alcohol

Every wine region measures ripeness by sugar, but almost every one uses a different scale for it. Brix, Baumé and Oechsle are three ways of reading the same thing — the density of the must, which tracks its sugar — and knowing how they relate saves confusion at the weighbridge and lets you read potential alcohol straight off a refractometer.

Three scales, one measurement

• °Brix — grams of sugar per 100 g of must (% by weight). The standard in the US and much of the New World.
• Baumé (°Bé) — a density scale where 1 °Bé ≈ 1% potential alcohol; traditional in France, Australia and Portugal.
• Oechsle (°Oe) — the last three digits of the specific gravity (SG 1.085 → 85 °Oe). Standard in Germany and Central Europe.
• Specific gravity — the raw density the others are derived from.

How they convert

The scales are all functions of density, so they interconvert exactly through specific gravity. As handy approximations: °Brix ≈ 1.8 × °Bé, and °Oe ≈ (°Brix − 3) × 4 near typical ripeness. For anything you act on, use a proper conversion rather than a rule of thumb — small errors in density move potential alcohol by tenths.

Potential alcohol: divide sugar (g/L) by ~16.8 to estimate %vol. A must at 22 °Brix carries roughly 240 g/L of sugar → about 13% potential alcohol.

From reading to decision

Must weight is only one leg of the ripeness decision — pH, titratable acidity and phenolic (flavour and tannin) ripeness are the others — but it is the one that sets the alcohol you will end up with and whether you need to enrich or, in a hot year, consider the reverse. Track it across maturity samples and you see the curve, not just a single day’s number.

In GrapeFlow every maturity sample and fermentation reading is stored against the block and lot, so the ripening curve and the fermentation curve draw themselves.

Conversions assume a sugar-dominated must near 20 °C; confirm potential alcohol against your own results.