Must weight

Lore & Background

In France and many other countries, grape must density is often recalculated to show potential alcohol, the percent alcohol content that would result if the must were fermented to a completely dry wine. Various measurement scales exist for must weight, including Brix (°Bx) used in Italy, France, and Canada; Klosterneuburger Zuckergrade (°KMW) used in Austria, which measures exact sugar content; Normalizovaný moštoměr (°NM) used in the Czech Republic and Slovakia; Baumé scale (Bé°) occasionally used in France and by U.S. brewers; Oechsle scale (°Oe) used in Germany, Luxemburg and Switzerland, an important part of German wine classification; and relative density used in the United States, though Brix is sometimes used there as well.

Must weights are commonly measured in the vineyard using a refractometer. A few grapes are crushed between the fingers and the must is dripped onto the glass of the refractometer. The refractometer is calibrated in a must weight scale, but as refractometers actually measure refractive index, the must weight scale is an indirect measurement, with refractive indices having been pre-converted to their must weight equivalents.

Reader's Guide

Must weight serves as a fundamental tool in winemaking, particularly for determining harvest timing. By measuring sugar concentration in the grape must, vintners can estimate the potential alcohol content of the finished wine if all sugars are fermented to dryness. The variety of measurement scales reflects regional traditions and classification systems: the Oechsle scale is integral to German wine classification, while Brix is widely used across Italy, France, and Canada. The KMW scale in Austria directly measures exact sugar content, and the NM scale serves the Czech Republic and Slovakia. The Baumé scale finds occasional use in France and among U.S. brewers, while relative density is the standard in the United States, sometimes alongside Brix. The practical measurement method—using a handheld refractometer in the vineyard—allows quick, non-destructive sampling by crushing a few grapes and reading the refractive index, which is converted to a must weight equivalent. This indirect measurement approach enables winemakers to assess ripeness efficiently, making must weight a key parameter in the decision to harvest.

Did You Know?

• Must weight indicates the amount of alcohol that could be produced if all sugar is fermented to alcohol.
• The Oechsle scale is an important part of German wine classification.
• Refractometers measure refractive index, which is pre-converted to must weight equivalents.