General infection question

[dbrewski]

So I have had a couple of batches that I think were infected. They were not spectacularly infected, with horrifying moldy-looking things growing, they made it all the way into the keg without tasting off or looking bad. I sample the beer before kegging when I measure the FG and it tasted fine.

By the time I tapped the kegs, they were cloudier than they should have been, and more bitter than I remembered them. They continued to get more bitter over time, almost undrinkable, and one started having excessive foamy head on it. So on reading posts here, I think it is infection, maybe somehow in the keg or serving lines?

So in general, I thought that beers were pretty safe from infection after they fermented. Is this not true? Or to put it another way, can serving lines, taps, disconnects, etc harbor nasty stuff that can infect a finished keg of beer?

and question 2 can beer in your CO2 lines that backed up grow bad stuff? I had a co-worked share with me his thoughtst that nothing bad grows in the absence of oxygen. not that he was saying "don't clean the beer out", just in general he was saying infections dont' come from gas lines.

I am trying to figure out a starting point, any thoughts are welcome!

 

[ChessRockwell]

I've never heard of infections causing the beer to get more bitter, usually sourness is what people describe. I'm not much of an expert on infections or kegging systems though, (I only bottle) so I'd be interested to hear what others say. It seems to me like serving lines/etc. could be dirty and cause an off flavor, but I wouldn't call that an "infection" unless it had a way to get back to the keg to grow and prosper. Again, don't know much about kegging systems but I know beer in restaurants can taste like s--t if the lines aren't clean.