Proof
Beers, wines and spirits bought in the UK usually have somewhere on their label a figure that says something like 13% Proof.
Proof is old measure of the strength of an alcoholic drink. It has its origins from the days when a test was needed to show that the drink did really contain a 'correct' measure or significant amount of alcohol. The test was applied as follows :
- Some of the drink was poured over a little gunpowder.
- The alcohol was ignited.
- If the alcohol content of the drink was adequate, then it would burn with a steady blue flame...
- leading eventually to the ignition of the gunpowder.
If the powder burned, then the drink was proved (hence proof of its alcohol content!)
This procedure was later replaced by a test using an instrument known as a hydrometer to measure the specific gravity. This was far more objective and allowed people to give a much better indication of the amount of alcohol in a given batch of beer or wine or spirit.
