If you're making a batch of homemade wine, you'll want to test the alcohol content before drinking or serving to make sure it's not too potent or too weak. The easiest way to measure the alcohol content is to use a special tool called a hydrometer, but this method requires some planning in advance. To measure the alcohol content accurately, you must take a reading of the fruit juice you are using to make the wine before fermentation, as well as after.
Place a sample of the fruit juice to be fermented (the "must") into a test tube, using the baster or wine thief. Fill the tube until it is 3/4 full.
Place the hydrometer inside the test tube. With your thumb and forefinger, spin the hydrometer gently to remove any air bubbles on the sides of the instrument.
Read the Potential Alcohol level off the scale printed on the side of the hydrometer. Take the measurement of the liquid at eye-level.
Take a second reading when the fermentation process is complete. Use the same method described above for taking a sample of the wine and reading the Potential Alcohol scale.
Subtract the potential alcohol reading after fermentation from the reading before fermentation. The difference between the two numbers is the alcohol content of the wine. So, if you had a reading of 12 per cent before fermentation and a reading of 2 per cent after fermentation, the alcohol content of the wine is 10 per cent.
Lower-strength wines are prone to going bad faster. For storage purposes, your wine should have an alcohol content of at least 9 to 10 per cent. If alcohol content is on the low side, add sugar to the wine to increase its level of alcohol.