I was wondering why this became the standard, at least in the U.S. I tried to Google the question but just found a bunch of stuff about why the word proof is used and it being equivalent to half of a percent. The question I want the answer to is why most are 40% abv and not a higher or lower amount.
The standard until a few years ago was 86 proof. They dropped it a bit to make more money. It was rather amusing to watch every distillery try to explain the change by any means possible other than sheer economics.
In the US 80 proof is the minimum allowed by law for many spirits (link).
When is a few years ago? I was only a kid in the 80s, but even then I remember 80 proof being the most common for hard alcohols. Am I misremembering?
Duplicate post
I remember sometime in 1987-88, Jack Daniel’s black label went from 90 to 86 proof. A liquor store owner I knew told me it was because the federal tax was based on the proof, and had recently gone up. So rather than raise the price, they lowered the proof. (And affected the taste, IMO)
Now JD black label is 80 proof, and costs more than it did 25 years ago.
Yeah, Jack is one of the ones I do remember not being 80 proof. I think they went down to 80 some time in the early 2000s, IIRC.
And just to elaborate for the OP in case it isn’t clear, spirits are distilled and aged at quite high proof, and then brought down to bottling proof with the addition of water - so a lower proof makes a given bottle cheaper to produce.
According to Wikipedia, Jack Daniel’s was 90 proof until 1987, when it went to 86 proof, and in 2002 they lowered it again to 80 proof. They apparently claimed that this was because consumers preferred a lower-proof whiskey. At least, that was what they claimed once people noticed that they’d done it. Here’s an article about it.
Yeah, that gibes with my memory. The reason I remember it is because I was living outside the US from 1998-2003 and upon my return, I discovered something had changed about the Jack Daniel’s. Turned out to be more watered down. It did take me awhile to figure it out, though, as I don’t drink Jack straight usually.
By distilling ethanol - a best concentration of about 96% by volume (192 proof) can be obtained.
192?! That’s nuttin’! 
Actually what I am wondering is more why the most prevalent number seems to be 80 not 85, 75, 70, 93 or anything between like 30 proof and 190 proof can be found in the liquor stores in America but over half of the inventory in a store is exactly 80.
This maybe explained by Game Theory ( Nash Equilibrium - Competitive Strategy).
Well clearly it’s consumer preference. Can’t be the expense. Nope. Choice quote from the linked article:
:dubious:
I looked for a cite on Wikipedia last night and couldn’t find it, but I believe that 80 proof is the lowest proof allowed for anything sold as whiskey (or possibly “straight whiskey”) in the US.
ETA: Found it! Eighty proof is in fact the legal minimum for any distilled spirit except “blended applejack” and liqueurs.
There’s a good number of 100 proof. I like drinking something that can ignite. I don’t know if I could honestly perceive the difference between 80 and 86, but 80 vs 100 is obvious.
Excellent post/username combo!
A related question:
Why proof? Who came up with this measurement? It looks like proof = twice the percent of alcohol by volume right? Why not just use alcohol by volume?
The term came from the U.K., and was based on the spirit’s ability to sustain the combustion of gunpowder. 100 proof was the amount of alcohol in the beverage which was needed to do so – it was actually ~57% alcohol by volume, though the U.S. definition of proof is somewhat different.