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You need a hydrometer to measure the alcohol content of a drink and determine its proof, or twice the percentage of alcohol it contains when tested at 60 degrees Fahrenheit. In addition, the type of drink -- distilled spirit, wine or beer -- determines the scale needed to interpret the hydrometer's specific-gravity measurement. A hydrometer, a simple device based on Archimedes' principle, consists of a piece of stemmed glass with a bulbous base that measures the force exerted on it by the drink. You need a proof and Tralles hydrometer for distilled spirits, and a triple-scale hydrometer for wine and beer. A precision-finished hydrometer, which has smaller gradients, measures finished drinks.

Using the Hydrometer

Set the hydrometer's glass cylinder on a level table. Draw the distilled spirit, wine or beer into a food-grade pipette and release it into the glass cylinder -- add enough of the drink to fill the cylinder about 3/4 full. Insert the hydrometer in the drink gently and spin it as you let go of it -- this dissipates any bubbles touching its base. Wait for the hydrometer to come to a rest in the drink.

Reading the Hydrometer

Examine the hydrometer's specific gravity reading at the bottom of the meniscus -- the concave surface of the liquid surrounding the hydrometer -- and record it. Next, compare the specific-gravity measurement to the potential-alcohol scale supplied with the hydrometer to arrive at the alcohol percentage. Multiply the alcohol percentage by 2 to determine the proof.

For example, if a wine has a specific gravity of 1.1009 as measured on the hydrometer, it has 13.8 percent alcohol according to the potential-alcohol scale, which equates to 27.4 proof.

About the Author

A.J. Andrews

A.J. Andrews' work has appeared in Food and Wine, Fricote and "BBC Good Food." He lives in Europe where he bakes with wild yeast, milks goats for cheese and prepares for the Court of Master Sommeliers level II exam. Andrews received formal training at Le Cordon Bleu.