Alcohol Proof

The regulation to proof alcohol was simply to test and verify that the contents of a barrel of liquid was what it was claimed to be began in England during the 16th century to ensure that the King collected the proper amount of taxes on the sale of the product.

The first method involved soaking a gun pellet in the liquid, and then trying to light it on fire; if it burned, it was classified as a proof spirit. However, as alcohol’s flammability is temperature dependent, the higher the temperature, the more vapors the alcohol infused solution will emit and therefore more flammable. Sometimes actual alcohol was passed off as something less and taxed at a lower rate.

Frequently the product would catch fire, and the authorities would know that the spirit was at least 57.15% alcohol by volume (ABV), which at that time was classified as being 100 proof.

As scientific skills improved during the early 19th century, a far more accurate test was developed which measured the liquid’s specific gravity (the ratio of the density of a substance to a reference, in this case distilled water). Distilled water is actually denser than alcohol. In 1816 a test was developed using the fact that at 11°C  (51°F), a 100 degree proof spirit (~57.15% ABV) would weigh 12/13 that of distilled water.

AnIPA with an ABV of 6.9% in the UK would be 12.075 degrees of proof, while a 100% ABV pure alcohol would have a proof of 175 degrees.

In the US, proof is calculated by doubling the ABV. So alcohol with an ABV of 40%, is 80 proof. Nevada, US prohibits the sale of alcohol in excess of 80% ABV (160 proof), and California, US prohibits the sale of anything over 60% ABV (120 proof).

The US has singled out one alcohol in particular for regulation – absinthe ABV (45-75%). It is infused with green anise, fennel, other herbs, and grand wormwood. During the early 1900s, a number of countries banned absinthe, due to a smear campaign conducted by the wine industry and the presumed presence of thujone, a chemical compound that is said to be poisonous in large amounts. It is now known that most absinthe has very little thujone and easily meets all regulatory requirements. Beginning in 2007, absinthe returned to the US as imports from Europe and with domestic producers.