Small journalistic gaffe, here. Alcohol Proof is about 2x the percent of alcohol (in the US).
“The term was originally used in the United Kingdom and was defined as 7/4 times the alcohol by volume (ABV). The UK now uses the ABV standard instead of alcohol proof. In the United States, alcoholic proof is defined as twice the percentage of ABV.
“The term originated in the 18th century, when payments to British sailors included rations of rum. To ensure that the rum had not been watered down, it was “proved” by dousing gunpowder with it and then testing to see if the gunpowder would ignite. If it did not, then the rum contained too much water and was considered to be “under proof”. Gunpowder would not burn in rum that contained less than approximately 57.15% ABV. Therefore, rum that contained this percentage of alcohol was defined to have “100° (one hundred degrees) proof”.
That’s an interesting explanation of “proof”, but something tells me that the idea of sailors getting cheated would not motivate people to come up with an idea for testing the alcohol ratio. After all, the poor sailors were treated pretty badly all around.
I did a search and found an article. It’s from the WaPo — yeah, I know — but this explanation sounds more plausible:
These days, most drinkers don’t have much experience with high-proof spirits. In the 18th century, proof was much more straightforward. Liquor was “proofed” at the distillery by adding gunpowder and lighting it on fire. If it didn’t light, the alcohol content was too weak. If it burned yellow, too strong. If it burned blue, the proof was just right (that was around 57 percent, or 114 proof). A century ago, our federal government established a standard that quality spirits were “bonded” at 100 proof, or 50 percent alcohol. You still see the word bonded on certain 100-proof bottles of old brands such as Rittenhouse Rye or Laird’s Straight Apple Brandy, but the term doesn’t really carry much weigh any longer. Over time, federal and state excise taxes on higher-proof spirits drove down the average proof, as did health concerns and consumer preference. Jack Daniel’s whiskey, for instance, dropped from 90 proof to 80 proof in 2004.