On Mon, 12 May 2008 03:24:01 +0100, Charles Ellson wrote

Is it written down anywhere how much alcohol needs to be in something
before it's "an alcoholic beverage"?

ISTR it used to be 2%.

You are confusing percentage (of alcohol by volume) with degrees
proof. 100deg proof = ~57 % abv ('Merkan measure is different).

Am I? I just remember cans of Shandy Bass in the late 60s with the warning
"contains no more than 2% alcohol"