A European joke about American beer is:
 
Q: Why is American beer served cold?
A: So you can tell it from urine.
 
The joke has been cited in print since at least 1991. David Moulton has been credited as the author since at least 1997.
     
 
Google Groups: soc.culture.british
Beer and Bacon
Fraser Orr
9/16/91
(...)
Q: Why is American beer served cold?
A: So that you can tell the difference between it and urine.
 
Google Groups: alt.tasteless.humor
Sick Humor from Funny Pages #49, Nov ‘93
Joe Workman
2/19/96
Hey, I publish a sick joke newsletter, Funny Pages.  Here’s an old issue—
there’s more of ‘em at:
http://www.erinet.com/jworkman/fphome.html
(...)
Why is American beer served cold?
So you can tell it from urine.
     
Google Groups: alt.pub.kacees
Beer
Kimberly Chapman
3/31/97
(...)
Why is American beer served cold? So you can tell it from urine.
—David Moulton
 
2 June 1997, South China Morning Post (Hong Kong), “Sutch a gent to keep fleet on the ground,” pg. 12:
Just a thought: “Why is American beer served cold? So you can tell it from urine.” (David Moulton, via James O’Connell.)
 
Google Groups: alt.games.grand-theft-auto
Valdez and his magic page
Hexuron
8/2/98
(...)
Why is American beer served cold? So you
can tell it from urine.
—David Moulton
 
Google Books
The Man Show on Tap:
A Guide to All Things Beer
By Ray James
New York, NY: Simon Spotlight Entertainment
2004
Pg. 38:
“Why is American beer served cold? So you can tell it from urine.” —DAVID MOULTON
 
Google Books
Alcoholica Esoterica:
A Collection of Useful and Useless Information as it Relates to the History and Consumption of All Manner of Booze
By Ian Lendler
New York, NY: Penguin Books
2005
Pg. 25:
“Why is American beer served cold? So you can tell it from urine.”—DAVID MOULTON
     
Twitter
Bob Kostic‏
@causticbob
Why is American beer served cold?
So you can tell it from urine.
12:29 PM - 21 Feb 2017
 
Reddit—Jokes
Why is American beer served cold?
submitted May 25, 2017 by CoolStoryMoe
So you can tell it from urine.