Why is alcohol measured by proof?
The answer involves lighting liquid on fire.
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Transcript
Have you ever seen the word âproofâ on the label on a liquor bottle and wondered, Proof of what?
Well, proof is one way of measuring a drinkâs alcohol content. The measurement system goes back to the 16th century, when the English government would tax spirits that had a certain higher alcohol content.
The English navy would test spirits by soaking a pellet of gunpowder in the liquor and trying to light it on fire. If it ignited, it was âproofâ of higher alcohol content, and the spirit would receive the proof tax.
This wasnât the most scientific way to test alcohol content. When you light liquor on fire, youâre actually igniting the ethanol vapor itâs emitting, not the liquid itself. That means a spiritâs flammability is dependent on its temperature as well as alcohol content: the warmer it is, the more vapor it will emit to light up.
Still, even at cooler temperatures, the more ethanol a liquor has, the more vapor it will produce. Although the navyâs method wasnât consistent, drinks that were above 50 percent alcohol by volume* were probably passing their test.
In 1816 the British government decided to make the measurement more official. It defined âproofâ liquor as having an alcohol level twelve-thirteenths the weight of the same amount of distilled water when resting at 51 °F. Thatâs about 48 percent alcohol by weight, or 57 percent ABV. Think rum, whiskey, brandy, or vodka.
Other countries took a slightly simpler approach. In 1848 the United States defined âproofâ as double the ABV, so a spirit with 50 percent ABV would be 100 proof.
France had taken it a step further. In 1824 scientist Joseph-Louis Gay-Lussac decided that 100 proof would equal 100 percent alcohol by volume, making proof the same as ABV.
By the 1980s, Britain and the rest of Europe had started using ABV instead of proof as the standard measurement for alcohol content. Listing proof is no longer a requirement and is rarely seen outside the U.S. So now you know: alcohol proof was originally âproofâ that a liquor could be lit on fire. Just⊠donât try it at home.
Still, even at cooler temperatures, the more ethanol a liquor has, the more vapor it will produce. Although the navyâs method wasnât consistent, drinks that were above 50 percent alcohol by volume* were probably passing their test.
In 1816 the British government decided to make the measurement more official. It defined âproofâ liquor as having an alcohol level twelve-thirteenths the weight of the same amount of distilled water when resting at 51 °F. Thatâs about 48 percent alcohol by weight, or 57 percent ABV. Think rum, whiskey, brandy, or vodka.
Other countries took a slightly simpler approach. In 1848 the United States defined âproofâ as double the ABV, so a spirit with 50 percent ABV would be 100 proof.
France had taken it a step further. In 1824 scientist Joseph-Louis Gay-Lussac decided that 100 proof would equal 100 percent alcohol by volume, making proof the same as ABV.
By the 1980s, Britain and the rest of Europe had started using ABV instead of proof as the standard measurement for alcohol content. Listing proof is no longer a requirement and is rarely seen outside the U.S. So now you know: alcohol proof was originally âproofâ that a liquor could be lit on fire. Just⊠donât try it at home.