A bit of history...
What is Proof Strength?
Alcohol Proof strength is another (older) measure of the strength of an alcoholic
liquid. It had its origins in days when a simple test was needed
that the liquor did indeed contain a *correct* measure (or more) of
alcohol. And it was indeed a simple test.
Some of the liquor was poured over a little gunpowder and ignited.
If the alcohol content was adequate, then it would burn 'just right'
with a steady blue flame and eventually ignite the gunpowder.
If
there was insufficient alcohol then it would fizzle out and the
gunpowder would be too wet to burn. The 'just right'
condition 'proved' the liquor and it was declared to be
100 Proof Vodka.
This simple test was clearly cumbersome to perform and was later
replaced by using a specially graduated hydrometer to measure the
specific gravity.
This was far more objective and allowed precise
statements to be made as to how much different it was from being
100 proof. This gave rise to "under-proof" and "over-proof"
measures.
Keep your powder dry (or wet it with the right stuff!)
At one time (in the days of sailing ships, cannons and gunpowder)
the makers of Plymouth Gin distilled a special gin for the Royal
Navy. It was 57%AbV or 100 proof.
Why?
In order to keep it secure it was stored in the magazine close by
the gunpowder. So, even if it leaked and wetted the gunpowder, at
100% proof the gunpowder would still explode.
Though that need has been long gone, they still market the stuff as Navy Strength!
