h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm not sure how the terms proof and overproof relate to the alcohol percentages by volume in drinks. We have a version in Oz called Bundaberg Rum which has an overproof bottle and comes in at about 51% from memory. Anyone like to fill me in on how the system works?

I not sure when or where proofing started, but it's fairly simple.
Pure grain alcohol, being 100% alcohol, is 200 Proof. So it follows that a bottle that is 50 proof contains 25% alcohol and so on. Most "hard liquors" are labled with a proof value but beer and wines are beginning to display an alcohol percentage on the labels instead. Your Bundaberg is most likely 102 proof.

Here in Pennslyvania, where all liquor is sold by the state goverment, we can't buy Pure Grain Alcohol anymore without pemit.
So we make due with 151 rum (151 proof) for our fruit punches.

Hope this helps.

I believe that the proofing system dates back to a old method
of checking the alcohol content of Whisky produced by the
stills in Scotland. As the people checking were soldiers rather
than analytical chemists a simple method had to be devised.

The method consisted of sprinkling a small quantity of Gunpowder
on a plate and pouring the test sample over it. A match was
applied to the gunpowder. If the powder ignited the spirit
was "Proved" - ie proof spirit. 100% proof was just enough
alcohol to allow the powder to burn. Above was explosive,
below just fizzled.

Yep, the gunpowder thing is right.

However whilst 100% proof is 50% by volume in America/Canada in Britain 100% proof is about 58% by volume; this being the weakest mix where the proof works (the powder burns).

The Americans changed it as they though that pure ethanol being just over 170% was a bit messy, and upping it allowed them to tax alcohol as if it was a little stronger.

Bez