Why does it smell like a wet dog when I drink draft beer out of a glass?

Beer that has gone bad will usually have an off smell. If beer is exposed to too much light, it will smell like rotten eggs or sulfur.

Tags: draught beersulfurglassbeereggs 
Wednesday, February 01 2012
Source: http://www.ehow.com/how_2212726_know-beer-goes-bad.html