- Simple subtraction. Take a hydrometer reading right before you pitch the yeast into your must (see “How do I take a hydrometer reading?” in FAQs).
- Make a note of this reading, which should be in the range between 1.060 and 1.120, depending on the recipe and style you are making.
- After the fermentation is complete, take another hydrometer reading right before you bottle. This reading will usually fall between 0.090 and 1.010, again depending on the style of wine made.
- Then you simply subtract the second reading from the first, and consult a conversion chart (such as the one found in “First Steps in Winemaking”, or many other winemaking books) to determine the alcohol content. Let’s say that your starting gravity was 1.085, and your terminal gravity was 1.010. This makes a difference of 0.75. Looking this up in the conversion chart will tell you that your wine is 10.4% A.B.V. (alcohol by volume).
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