I found this on a commercial brewing site.  It isn't used as a germicide, just as a cleaner.
Next time I brew up a batch of beer in my Westy, I'll be sure to remember this.

Bill

"Acetic acid, also known as white distilled vinegar, is a very effective cleaner for copper.
Brewers who use immersion wort chillers are always surprised how bright and shiny the chiller
is the first time it comes out of the wort. If the chiller wasn't bright and shiny when it went
into the wort, guess where the grime and oxides ended up? Yes, in your beer. The oxides of
copper are more readily dissolved by the mildly acidic wort than is the copper itself. By
cleaning copper tubing with acetic acid once before the first use and rinsing with water
immediately after each use, the copper will remain clean with no oxide or wort deposits that
could harbor bacteria."