The beer had a very sour rancid flavor that overwhelms all other flavors. The beer was also cloudy with a fine white haze. My uninfected beer tends to be very clear. Also this flavor increases with time so after about a week and a half the beer is so bad it is impossible to drink more than a couple of sips.
Since I don't have a microscope I am guessing this is acetobacter. Am I incorrect in this guess?
I thought of the bung thung also so I threw them out and ordered new ones.
Hmm... take a look at these off-flavor flash cards and see if you can pin it to one or two of those. http://www.beerjudgeschool.com/uploads/Beer_Characteristics_Flash_Cards.pdf
From your description, it sounds exactly like a bacterial infection (rancid, sour, cloudy & exponential growth are all signs of bacterial infection) - most likely acetobacter.
Correct me if I'm wrong, but here's what I see:
- Your brewing process seems sanitary due to the presence of uninfected beers.
- You're not sampling or even opening some of the infected beers.
- Glass carboys should be clean.
I don't know if the issue is just the freezer. Is there some sort of plastic equipment that you may just happen you use on these infected batches? Airlocks? Tubing? Bungs? Buckets? Are they sour in the fermenter or after bottling? If in the fermenter, that narrows it down. If after bottling, that opens up all of your bottling equipment to suspicion.
FWIW, I had a small phenolic infection in my brewery about 8 months ago. I did not chance wasting any more beer and threw out all of my plastic stuff and started again.