Booze

[andrewlee]

It was once explained to me and fellow diners and drinkers by a chemistry graduate the difference between per cent proof and per cent alcohol. Needless to say I didn't understand, nor can I remember the explanation. Can anyone assist, please?

[Clanad]

From The Indiana Prevention Resource Center: The strength of an alcoholic beverage is usually expressed as either the percentage of absolute alcohol by volume, or as "proof." In the USA, proof is a measure of the amount of absolute alcohol in distilled spirits, and is calculated as the number of parts of alcohol in 200 parts of beverage at 60 degrees Fahrenheit (a beverage that is 50% alcohol is "100 proof;" a beverage that is 43% alcohol is "86 proof"). Under the American system, one "proof" is equal to one-half percent of alcohol by volume.
A different system for measuring proof is used in England, In England, proof is measured by comparing equal volumes of water and the beverage at 51 degrees Fahrenheit. 100 proof is set at the point at which the beverage weighs 12/13th as much as water. This means that a beverage that is said to be 100 proof under the British system is 114.2 proof under the American system. A beverage that is 100 proof under the American system is said to be 87.6 proof under the British system.
A pint of pure alcohol weighs about 12.8 ounces. If one pint of pure alcohol is mixed with one pint of water, the result is a beverage that is 50% alcohol "by volume." If one pound of pure alcohol is mixed with one pound of pure water, the result is a beverage that is 50% alcohol "by weight." Since one pound of water 16 fluid ounces, and one pound of alcohol is about 20 fluid ounces, the 36 total fluid ounces in a resulting beverage is about 55.5% alcohol "by volume," although it is 50% "by weight."

[nickmo]

And you are bored one day, have a read through this.... http://www.projects.ex.ac.uk/trol/dictunit/booka.pdf which covers it all.

[Gef]

In the UK (and many other places) all alcohol containers are now marked with %ABV (alcohol by volume) and the proof system is not used.

Whisky, 40% ABV, was always described as 70 degree (not percent) proof.