Originally Posted by dizzyfun
A little more info about the recipe...
4# Marris Otter
3# British Crystel 60
Willamette 0.2oz @30min
Mystery Hop 0.5oz dry hop
BIAB 75 minutes
Sanitation shouldn't have been an issue. Sanitized with Iodophor at the same strength as I usually use, 15ml/5 gallons. I fermented in a glass carboy. I am thinking it's more a sour beer than spoiled because I tasted it at about the 1 month mark and it tasted fine but weak with no hops flavor which is when I added the additional hops. I suppose it could have been contaminatd by the hops. I dried the hops and put them in a bag but when I added to the beer they had not been frozen yet. Would freezing kill any bacteria?
If it is sour, it is infected with something - doesn't matter if it was intentional or not. Probably Lactobacillus, which would munch on that lactose (and other residual sugars) and produce lactic acid (the same thing that happens in making yogurt). I can only speculate that your sanitation wasn't as good as you thought...or something got in post fermentation. With a mild, you don't have quite the hostile environment that might prevent an infection from taking hold. Freezing doesn't really kill bacteria (I suppose it might to some degree, but should not be used as a sterilizing technique). But dryhopping is a very common practice that usually doesn't have issues - hops are naturally anti-microbial. Did you sanitize the bag?
As others have said, if you enjoy sour beers this might be something to hang onto and see where it goes.