The Fascinating Reason Alcoholic Strength Is Called “Proof”

The definition of the term “proof”: In the U.S., Is the percentage of alcohol, times two. For example, if a bottle of vodka is 40 percent alcohol, it’s 80 proof. But why exactly is it called “proof”?

The answer is a lot more interesting than you may think!

The term dates back to England in the 1500s, when spirits were taxed at different rates depending on their alcohol content.

Back then, alcohol content was tested based on a rather rudimentary method: A pellet of gunpowder would be soaked in the spirit, and if the gunpowder still burned, then the alcohol content was “proven” to be higher than 57.15 percent and taxed at a higher rate.

This type of spirit, with its high alcohol content was deemed to be “over-proof,” a term that’s still used in the industry for any spirit (usually rum) with an alcohol content higher than 57.5

This rather primitive way of approximating alcohol content didn’t stick around for very long; by the early 1800s it was replaced by testing specific gravity with a hydrometer, which is still the process used today.