What 'proof' on a liquor bottle really means

Dear Lynne,

Liquor labels always say “proof” (like “80 proof”). What does “proof” actually mean?

–Douglas from Minneapolis

Dear Douglas,

At first glance the definition of "proof" makes no sense. It seems needlessly complicated.

Proof is the government documentation of a distilled beverage’s alcohol content. In the U.S., if you cut the number in half, you get the actual amount of alcohol in the bottle. Eighty proof means 40 percent of the liquid in the bottle is alcohol. Why use proof when you could simply state "40 percent" on the bottle?

Proof began here during our 18th-century whiskey trade. Whiskey took off when farmers realized they could make 10 times the money on their corn if they distilled it. As the market soared, so did watering down the booze for even more money.

Suspicious buyers came up with a “gunpowder proofing” testing method. They mixed the whiskey with gunpowder and lit it. If the gunpowder exploded, the liquor had no water in it and it was “proofed.” And so was anyone standing nearby. This became the official term for pure whiskey. Please do not try this at home.

-Lynne