This question was posed at Reddit:
At an engagement party last weekend, my husband enjoyed a Beck's. He decided he would like to enjoy another and so opened this bottle, took a sip and cringed. His beer tasted awful and he wiped off what looked like dirt from the bottle cap. He held the beer to the light and the liquid was murky through the green glass there was something floating in it. We go in to the kitchen, pour the beer down the sink and something slipped out. I turned it over and it kind of looked like a mushroom and smelled a whole lot like shit. This image is the bottle and the offending object.Answer below the fold (it's not offensive - just giving you a moment to ponder...)
Two of the comments:
That's a Beer Oyster. It was caused by a pasteurization failure, the beer was not heated to the right temperature. Leftover yeast/bacteria were able to use the leftover air in the top of the bottle to survive and make a slimy, stinky mess. Source: My mother and brother work for major beer companies.
Close. At 2-3 minutes the pasteurization of 140F isn't going kill the yeast. Also through fermentation the environment is already inhospitable to the yeast. It has fermented out and can ferment no more. If it isn't fermenting it isn't reproducing. It isn't building yeast cake. Even so this would appear as a light film on the bottom as in a bottle conditioned beer.
What you are seeing is most likely a plate filter failure. It's going to be a mix of proteins, yeast and hop matter. Filter probably let loose a clogged bit at the end. It's unlikely to be an infection if the others were unaffected. Source: Homebrewer for 15 years, have brewed at a micro brewery.