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Alcohol Proof: Of Taxation and Libations

Check out Groupon’s guide to alcohol proof to learn the reasoning behind the way a drink’s potency is measured.

Different drinks pack different punches depending on how much they’ve been fermented and distilled—and the way that alcohol content is measured differs depending on where it’s made. The typical lager contains 4–5% alcohol by volume (ABV) and the typical whiskey or vodka rings in at 40% ABV, but spirits are more commonly measured in proof and chest-hair growth. In America, the typical whiskey is 80 proof—double the ABV percentage when measured at 60 degrees Fahrenheit. In the United States, the standard proof equals 100, on a scale that ranges from 0 to a theoretical 200. (In reality, not all water and barley tears can be distilled out of ethanol, making the maximum distilled spirit 191 proof).

The French scale, on the other hand, uses 100% ABV as 100 proof and 100% water as 0 proof—which would seem to be more straightforward. In fact, the apparent arbitrariness of the American system stretches back to the tax laws of 16th-century England. In those days, liquors were taxed according to the amount of alcohol they contained. To measure this, officials would soak a pellet of gunpowder in the liquor and put a flame to it. If the pellet burned steadily with a blue flame, it was considered “proof;” if it failed to burn, it would be considered underproof—likely watered down—and if it burned out quickly, it was overproof. “Proof,” it turns out, was roughly 57.1% ABV—roughly the same as a typical English 100-proof liquor today. Simplifying that system gave the United States its current double-sized scale.