Calculating ABV on old bottles?

[RegularChumpington]

Hey everyone,

I've recently come across a sample of Teacher's from the 50s or so, which is labeled as 86 proof. I recalled US proof (2x ABV) was not the same as proof in the UK (at least until 1980 according to Wikipedia).

I just wanted to see if someone could confirm my understanding here...

this, being bottled at 86 proof * 4/7 = 49.14 so about 49% ABV?

Just wanted to make sure I am understanding this correctly.

[John Barleycorn]

Your calculation is correct, but it seems to be a very odd proofing, unless the figure given on the label is already a US proofing, as it was intended for the US market. In which case an 86° US proofing would be equivalent to 75° British proof or 43% ABV; this seems to make more sense as whisky exported from the UK was always exported at a higher proofing which was equivalent to 43% ABV.

[RegularChumpington]

Ahhh, OK. That makes a lot of sense! I didn't think of it that way; I'd just assumed all bottles had the British proofing on it. Didn't even think of local labeling laws.

I'll ask a couple more questions but this makes a lot of sense. Thanks much!

[kallaskander]

Hi there,

I can not say much to your original question. Not with the complexity of the US rules on alcohol.

But one thing about the conversion of British proof.

The factor is 1.75.

Divide British proof by 1.75 to geht the abv.

Multiply the abv by 1.75 to geht British proof.

Saves a little time.

Greetings
kallaskander