How to Use a Hydrometer for Testing Wine

From homemade plum wine to traditionally crafted Sicilian Nero D'Avola, every wine is the result of chemical and biological reactions. The most important of these -- the conversion of sugar into alcohol and carbon dioxide -- is performed by yeast. The sugar content of the unfermented juice is measured to determine potential alcohol. As yeast eats sugar in the unfermented juice, which is called "must," the sugar content drops until there is none left, or until the winemaker halts fermentation to leave residual sugar for sweetness. Throughout this process, the winemaker measures the sugar with a hydrometer, a glass instrument that measures liquid density.

• 1

  Make a sanitizing solution by mixing 1 gallon of warm water, 1 tablespoon of citric acid and 3 tablespoons of potassium metabisulfite in a 1-gallon glass or plastic container. This will make enough sanitizing solution for 10 to 20 readings and will remain usable for more than a year, provided it is sealed when not in use.

• 2

  Sanitize the hydrometer, wine thief, thermometer and glass cylinder. Then rinse them and place on a sanitary surface to dry. Make sure your hands are sanitary as well.

• 3

  Measure the temperature of the must by placing the thermometer in the must and allowing it to float for 5 minutes. Record the temperature and then set aside the thermometer.

• 4

  Remove enough must to fill the glass cylinder. Then allow the hydrometer to float freely by placing the relief-valve end of the wine thief into the must and sucking the other end. Empty the wine thief into the glass cylinder by gently pressing the relief tab of the wine thief against the inside of the cylinder.

• 5

  Place the large end of the hydrometer into the must in the glass cylinder. Twirl the hydrometer gently to release any clinging air bubbles. Gently release your grip on the hydrometer.

• 6

  Allow the hydrometer to come to rest. Record the number on the hydrometer where the must meets the hydrometer. This number will be either a specific gravity reading (for example, 1.060), a degrees-Brix reading (15, for instance), or a potential alcohol reading (5 percent, for example). The specific gravity tells you the density of the liquid compared with pure water at 60 degrees Fahrenheit. The degrees-Brix reading tells you the percentage by weight of must that is sugar. The potential alcohol reading -- taken at the beginning of fermentation -- tells you what percentage of alcohol your wine will have if all the sugar is fermented out or converted to alcohol by yeast. These three readings can be converted to one another by using the Brix/Balling/Specific Gravity Chart (see the Resources section).

• 7

  Remove the hydrometer from the glass cylinder and pour the must from the glass cylinder back into its original container or a glass for tasting.

• 8

  Clean and sanitize the wine thief, glass cylinder, thermometer and hydrometer.