Definition - What does Must Weight mean?
Must weight is the measurement of the sugar content in grape juice (must). This is the amount of sugar in the unfermented must.
The amount of sugar will help the winemaker determine the potential alcohol of the finished wine, and this measurement is taken by using a refractometer or by the use of a tool that uses specific gravity, like a Brix or balling hydrometer.
WineFrog explains Must Weight
As the growing season comes to an end and grapes begin to mature, winemakers take field samples of grapes. The grape samples are then mixed together and separated according to their variety. They are then mashed so that the sugar in the juice can be measured with a refractometer. This helps determine when the grapes will be ready for harvest. Other factors are also measured, such as titratable acidity.
When grapes are harvested and crushed, the juices in the tank are also measured for their must weight. In some countries, such as Germany and Austria, it is important to know the must weight of each crush, as this is how they rank and label the finished wine. This is measured by the Oechsle scale.
In other countries, must weight is measured by Brix or Baumé.