Off taste in beer with particles floating?

Wasn't really sure where to post this question, since it doesn't pertain to a "home brew", but is just a general question about beer in general.

After I purchased my keezer, while I was waiting for two homebrews to finish fermenting I purchased a 1/6 keg of ShockTop *dodges thrown bottles* because I was anxious to use my new setup. Everything was fine for a while, or at least as fine as it can be with a cheap mass produced beer.

Due to error on my part, a significant amount of beer leaked out into the fridge, and led me to discover that I had also set the temperature too low because it froze to the bottom. I placed the keg outdoors overnight to thaw out (temperature was in the low 40's outside) while I cleaned the fridge. The next day I placed it back in the fridge in the afternoon. The high for the day was in the mid to high 50's, so thats the highest temp the beer could have reached.

It's been about two weeks now, and when I pour a glass the beer
(a) appears more cloudy than it used to be
(b) has little off-white particles floating around
(c) tastes funky, like something I've never tasted before. A nasty buttery flavor is the best I can describe it

What happened? Did the rise in temperatures cause a secondary fermentation to begin? Did freezing the beer some how mess it up? Is it at all salvageable?

Thanks for indulging my curiosity!

I'm thinking the possible causes of the off flavors in your beer are infection and oxidation (exposure to air). The buttery flavor in your beer could be diacetyl. The following quote is from 'Beer Me! - Down with Diacetyl!':

"One possible source of diacetyl is bacterial infection. Pediococcus and Lactobacillus are notoriously prodigious producers of diacetyl. So it's always a good idea to review your sanitation procedures; if you've got other problems like sourness, “rope”, and other nasty off-aromas, infection may very well be your problem."

Having said that, if I am not mistaken diacetyl is usually formed during fermentation and when the beer is vulnerable to infection (while in the fermenter). I suppose it's not impossible that a post fermentation infection could occur, though. Not sure about the off white particles but they could be the result of an infection as well. About the cloudiness, isn't Shock Top supposed to be somewhat cloudy?

Anyways, hope this helps somewhat.

You're correct, it is supposed to be somewhat cloudy, but its current state is definitely noticeably more cloudy that it was prior to this issue. Since it's contained in a commercial keg I'm unsure of how it could have been exposed to infection or air, but that description of nasty off-aromas definitely sounds on point.

I'm thinking that because the beer leaked there was also a possible entry point for infection. The increased cloudiness could also be a result of that infection or it could be chill haze. Definitely odd though as I have not heard of many finished beers getting infected.. although if the beer is old enough it could also be the result of staling. Freezing shouldn't have hurt the beer but it could have produced a structural change in some of the floating particulates that may have resulted in the off white particles. Just speculation, though.