Liquor drinkers throw the word proof around like it’s a badge of honor, not really understanding how that honor was earned. Proof is a big part of a whiskey’s description, letting the drinker know how much alcohol they are about to consume.
In the United States, it is required by law for every alcoholic beverage to list its alcohol content by volume. On a whiskey bottle, the proof will be listed right next to that, and reflect exactly two times the alcohol content. This may seem superfluous, but the reasoning is imbedded in the history of spirits.
Whiskey “Proof” is Explosive
Three centuries ago, the production of whiskey was rudimentary. There were no high tech tools lying around to help distillers figure out how much alcohol their blend contained. The best way (at the time) to find out was to pour a small amount over gunpowder and set it on fire.
Whiskey that had been diluted would not spark the wet gunpowder. Instead, it would quickly fizzle out. This showed that there was a very low alcohol content to the bottle. Strong whiskey would cause the gunpowder to catch fire, and even spark, giving the distiller the “proof” they needed that their blend was an intoxicating one.
Eventually the method became a little more scientific, and numbers were assigned to indicate the point at which there was enough alcohol in the whiskey to spark the gunpowder. In some cases, that point was too much, which is why we sometimes see a proof that is over 100.
Proof Becomes Outdated
In the 1730s, the hydrometer was invented, which allowed for a more accurate measurement of the alcohol percentage per volume. This eliminated the need to waste good whiskey by setting it on fire. Still, the term stuck because by that point that is what the consumer expected.
By the turn of the 19th century, United States distilleries had a very simple method of measuring alcohol by volume in place. The government began requiring that the alcohol content be displayed by percentage on each bottle. This is the ABV number you see printed. Whiskey distillers are still allowed to print the proof as well, which is twice the amount of alcohol, even though that information is technically already there.
So Why Keep Proof?
Since the bottling laws in the U.S. obligate whiskey distillers to list the actual alcohol content as a percentage by volume, having the proof displayed would seem redundant. Yet, traditionalists prefer to refer to their favorite spirit by its proof. Just imagine how it would sound asking for a Jack Daniels, 50% alcohol to your local bartender. A glass of 100 proof Jack straight just sounds cooler.
The art of distilling whiskey has been evolving for centuries, yet there are some components that we are just not willing to give up. Distilleries may have abandoned actually setting their liquor on fire, but the word proof won’t ever lose its place on the bottle’s label.