What is with the “Proof” to determine How Much Alcohol?

One Keg of Gunpowder

     In the early 1700s, the alcohol content of distilled beverages was determined by using gunpowder. A beverage  would be “proved” acceptable by pouring some on  gunpowder and lighting it. If it burned steadily with a blue flame, it was considered 100 degrees “proof” and equaled 57.15 ethanol, i

One Keg of Rum

n the United Kingdom, 100 proof equals 57.1% ethanol by volume. The historical origins of this definition can be seen in the gunpowder test.

     In the United States, proof is defined as double the percentage of alcohol contained in a solution at 60 degrees Fahrenheit or 15.6 degrees Celsius.  Thus, 150 proof would be 75% alcohol and 100 proof would be 50% alcohol.

Today's Labels show ABV and Proof

     Internationally, alcohol strength is measured according to the recommendation of the International Organization of Legal Metrology. The alcohol content of a beverage is measured by distilling off the alcohol, by measuring the volume of alcohol distilled and expressing it as a percentage of alcohol by volume (ABV) at a temperature of 20 degrees Celsius or 68 degrees Fahrenheit.

     This is how it came about and why we still talk about alcohol content in terms of proof.  It seems that we are moving rapidly though toward ABV to replace the old term "proof".   ;o)