Hydrometer

hydrometer, an instrument used for measuring the soluble solids, sugar content, or must weight of juice and wine before and/or during fermentation, consisting of a closed glass tube with a bulbous base, weighted so that it floats upright. The floating depth is inversely proportional to the density of the solution and is read by matching the bottom of the meniscus against a scale within the stem. This scale may be calibrated as for baumé, brix/Balling, oechsle, or % alcohol by volume (see alcoholic strength). As with all such density measurements, correction for the temperature of the solution is necessary.