Infected Beer?

I'm now on my 11th batch now and believe I have made 2 infected batches. My 6th batch (AG American Ale) and 11th batch (AG Pale Ale). Both done in my Better Bottle. I used the same recipe (AG pale ale) for my 10th and 11th batch. 10th one done in a glass carboy and the 11th in a 6g Better Bottle. The two beers have been bottled now for about 4 weeks. The 10th one tastes great with no off flavors. The 11th batch is pretty much undrinkable (and I have a very strong stomach) - I have tried multiple bottles. It is extremely sour and has a terrible smell. Makes you sick to your stomach after a couple sips. It smelled bad when I bottled it as well but didn't think too much about it.. I use starsan for sanitizer and am careful about the process. I think the problem is my 6 gallon 'better bottle' - may have been scratched? This is the only thing I can find in common with what may have happened. No infections yet when I use my glass carboy or plastic bucket. The 6th one and 11th one taste identical - both sour and undrinkable. There does not appear to be an infection on top of the beer while in the fermenter. It has been about 6 weeks now since the 6th batch has been in bottles - the taste is awful - completely undrinkable. Is it common for a better bottle to become scratched?

 

I shouldn't think so, unless you are using a carboy brush to clean it (which is a no-no).

Other than that, what are you putting into your carboy? The only thing that goes into mine is my brew and my fermtech thief. Neither should scratch it. I use my bottle cleaner to blast hot water into the BB and that is all the cleaning it usually needs, then I sanitize with starsan before my next brew.

 

Whoops. I've been using a carboy brush to clean it.. Bet this is the cause..