Must Weight

must weight, important measure of grape ripeness , indicated by the concentration of dissolved compounds in grape juice or must. Since about 90% of all the dissolved solids in grape juice are the fermentable sugars (the rest being acids, ions, and a host of other solutes), any measurement of these solids gives a reliable indication of the grapes’ ripeness, and therefore the potential alcohol of wine made from them (see fermentation).

Must weight may be measured approximately in the vineyard before harvest using a refractometer, or in the winery, using a refractometer or a hydrometer, calibrated according to one of several different scales used in different parts of the world for measuring the concentration of dissolved solids. This variation is not so surprising when one considers how crucial this statistic is to the winemaking process and therefore how early in the evolution of each country’s wine industry a scale will have been adopted. Each scale merely requires a different calibration of the hydrometer, usually with a reading of zero indicating that the density of a solution is exactly one, as in pure water.