My recent batches have all had a vinegar flavor to them. From my research so far I gather that they are probably getting contaminated. However, this last batch was so clean I don't see how it could be so.
Equipment that touches the wort:
Glass carboy - old but well sanitized
Copper coil wort chiller - sanitized and put in at 20min on the boil
Plastic Funnel. - Bought a new one and sanitized it
Metal aerator - Well sanitized
If anybody can think of something causing this problem it would be much appreciated.