Aeration

You know how they describe the taste as "wet carboard" when this sort of thing happens?..... pretty good description if you ask me. (But yeah, I still drank them anyway ).

 

When you are transferring beer and see bubbles forming in the tubing, that might be disolved CO2 coming out of the solution due to agitation and/or reduced pressure. Try duplicating the process with still water (non aerated) and see if you get the same bubbles. If you don't get the bubbles, then they came from disolved CO2 not air getting into you flow.

 

Whooops, my bad! BA on phone = tiny avatars.