"Proof" is a measurement of how much alcohol is in a liquid. The term was originally used before there was a reliable way to accurately determine alcohol content. In the original proving test, a small amount of the liquid to be tested was poured on a bit of gunpowder and exposed to flame. If there was enough alcohol in the liquid, it would burn and eventually ignite the gunpowder. Liquid with too little alcohol would simply wet the gunpowder and prevent it from igniting. Modern precision thermometers and hydrometers allow for much more accurate estimations of alcohol content.
- Skill level:
Things you need
- Large drinking glass
Examine the side of your hydrometer, or the instructions that came with it, to find the temperature for which it is calibrated. Most hydrometers are calibrated for 20 degrees Celsius (20 degrees Celsius).
Use a thermometer to find the temperature of the alcohol you intend to test. Warm or cool the alcohol to the temperature for which your hydrometer is calibrated. The closer to the correct temperature the alcohol is, the more accurate you results will be.
Pour the alcohol into a tall thin vessel, such as a tall drinking glass, until it is close to full. Slide the hydrometer into the glass without touching it to the sides. Gently swirl the hydrometer to dislodge any bubbles that may have clung to its sides or bottom. Since alcohol is lighter than water, the hydrometer sinks deeper into liquids of higher alcohol content. Read the measurement on the side of the hydrometer even with the surface of the alcohol.
Tips and warnings
- If your hydrometer measures in alcohol by volume (ABV), you can calculate the proof simply by doubling the percentage the hydrometer finds.
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