Go to almost any brewery or distillery and you will see lots of gleaming copper. This is not some quaint historical holdover nor is it there for show. We use copper in brewing for real and practical purposes. The reasons for using copper were well understood by the Colonial Brewer but why it worked has only been elucidated in the last 10 years.
Copper kills bacteria, viruses, and yeast on contact . This, along with heat and good technique, is one of the few truly effective ways the Colonial Brewer has of keeping his beer free of microbial contamination. Furthermore, unlike iron which is also toxic to yeast, copper only kills in its metallic form not in solution. Wort boiled in copper kettles will still grow yeast whereas wort boiled in iron kettles will not.
1 — Grass, Gregory, Christopher Resing and Marc Solioz; Metalic Copper as an Antibacterial Surface; Applied and Environmental Microbiology; March 2011, pp 1541-1547.