Why do we measure alcohol content in proofs?

[Lakai]

What is the point of saying something is 151 proof when we could easily go by alcohol percentages?

The proof is just twice the percent of alcohol. It seems redundant to double that number to come up with a proof number so that people can then divide that by two and get back to the original number. Which is all people want to know anyway.

What is the SD on this?

[John_Mace]

It’s a little more complicated, but essentially it’s just the traditional way that alcoholic content was determined. Proof (alcohol).

This system dates to the 18th century, and perhaps earlier, when spirits were graded with gunpowder: A solution of water and alcohol “proved” itself when it could be poured on a pinch of gunpowder and the wet powder could still be ignited. If it didn’t ignite, the solution had too much water in it and the proof was considered low or “underproof”.

A “proven” solution was defined as 100 degrees proof (100°). This has since been found to occur at 57.15% ethanol. This is still used as the British definition. A simpler ratio to remember is 7:4, i.e. 70° proof is approximately 40% alcohol by volume. Thus pure alcohol is approximately 175 degrees proof (175°).

Gotta love wikipedia. (I once looked this up, so I knew it was there.)

[Lumpy]

Wikipedia on “Proof”. Originally, proof was close to, but not quite, twice the alcohol content by volume. The current system dates to the time when it became more accurate to measure by hydrometer, and the precise conditions of measurement (temperature, etc.) have been tweaked to improve standardization of measures.

[psycat90]

Already answered, but here’s one more cite for the heck of it. (pdf)

[Lakai]

So if I go to England the proofs will mean something different?

I actually read the Wikipedia article before posting. The origin of Proofs is interesting but it does not explain why we are using that system now. Why do we still need a different way of stating alcohol percentages? What would happen if we suddenly stopped writing proofs on bottles and replaced them with alcohol percentages?

[John_Mace]

@Lakai

Why do we still need a different way of stating alcohol percentages?

We don’t.

What would happen if we suddenly stopped writing proofs on bottles and replaced them with alcohol percentages?

Nothing. So why do we keep doing it? Who knows. It sounds cool? No one wants to be first to change?

[Celyn]

@John Mace

We don’t.

Nothing. So why do we keep doing it? Who knows. It sounds cool? No one wants to be first to change?

It’s all right - Britain changed over to using percentage of alcohol by volume some years ago, so you don’t need to be first.

(I liked that bit about the gunpowder - I had never heard of that before.)

[FluffyBob]

The standard has certainly been percentage by volume as long as I have been buying alcohol here in Canada. I seem to recall the odd bottle of american liquor with a proof rating on the label in addition to percentage.

[psycat90]

It’s not required, it’s optional on a label in the US and nothing at all would happen if we stopped using it (other than perhaps some puzzled consumers noticing it’s gone?) I’m sure there are plenty of spirits out there that don’t list proof. As to why some spirits choose to list it I couldn’t say, perhaps not to puzzle consumers.

ABV is mandatory however.

[Malacandra]

@Lakai

So if I go to England the proofs will mean something different?

Yes. Eighty proof over your side of the pond is 40% ABV, but here we call that seventy proof (which is the typical strength most spirits are sold at).

[groman]

@Malacandra

Yes. Eighty proof over your side of the pond is 40% ABV, but here we call that seventy proof (which is the typical strength most spirits are sold at).

Does that have anything to do with the fact that I keep seeing things passed off as liquor that are 35% ABV or is that because 40% ABV would ruin the delicate “Artificial Strawberry Flavor” retch