An alcohol hydrometer is a tool used to measure the alcohol content in liquids, particularly in beverages like wine and beer. It works by floating in the liquid, with the level at which it floats indicating the specific gravity, which can then be converted to an alcohol percentage. These instruments are typically made of glass and contain a scale marked in degrees of alcohol. To use an alcohol hydrometer, you fill a test jar with the liquid, gently lower the hydrometer, and read the measurement at the surface of the liquid. This helps producers and home brewers determine the strength of their drinks.