Ever notice that 'eighty proof' liquor is only forty percent alcohol? Why do booze-makers feel the need to inflate their numbers like this?


It turns out this weird measure of alcohol content comes from an early test that people used to perform... which involved trying to make their alcoholic beverages explode.

As we speed towards New Year's Eve, with its mandate to get blearily drunk and try to act like you're not thinking about going back to work tomorrow, the mind turns to thoughts of liquor. That liquor is going to be flowing from bottles often marked 'XX Proof.' And the fact that this number is double the actual alcohol content of the liquor can make you feel even drunker than you actually are. What's the reason for spirits being sold with this archaic 'proof' system?


It all began when people in the British Navy came up with the brilliant idea of mixing alcohol and gunpowder. When the sailors did this, they noticed that gunpowder in alcohol would ignite — but only when the alcohol was not too watered down. Always on guard against deficient rum, the sailors learned to mix in gunpowder, and try to set fire to the lot. The flame was considered the 'proof' of the alcohol content. Only a keg, cask, or bottle, with sufficient 'proof' was purchasable. From this imprecise and ancient method came our current system.

Drunken sailors weren't the only ones interested in determining the alcohol content of various liquors. Spirits were taxed according to their alcohol content. Tax collectors used hydrometers, which worked on Archimedes' Principle — an object in liquid will be pushed up with a force equal to the weight of the displaced fluid. Alcohol is less dense than water, so a fluid made of equally mixed alcohol and water will let a weight sink or float, depending on the proportion of the less-dense alcohol to the more-dense water. Merchants often added molasses or sugar to make the liquor more dense, and fool the tax collectors.

The official British 'proof' — or one hundred proof which corresponded to a level of taxation — was eleven parts alcohol to ten parts water. Variations from there were rated as either 'over' or 'under' proof. Since then, most countries established their own 'proof' system. Early versions of the American system had the British eleven-to-ten proof as 114 proof alcohol. Because this is more impressive, and more old-timey, than stating the outright alcohol by volume, we are stuck with the proof system. Most countries, though, require all alcohol producers to state the outright alcohol content by volume somewhere on the bottle.

It would be more fun if we just tried to make it explode, though.

Image: The Collared Sheep

Via Dicas, Think Quest, and the Huffington Post.