What does proof mean on a liquor bottle?
It’s a measure of the percent of alcohol by volume, with proof divided by 2 equal to the percent. It’s based on a test they used to do with whiskey whereby when whiskey was 50% alcohol it would (when mixed with some other stuff) burn a certain way (i.e., it would be capable of igniting but without burning too quickly). Since 50% was the desired result of the distillation process, it was considered 100 proof, and that 1/2 ratio is used then for all liqour, whether it is 30 proof (15% alcohol) or, like Bacardi 151, 75.5% alcohol.
