What happens when you overchill your beer and go to raise it's temp a bit with a propane torch.
(in my defense I do do this regularly when I've left beer in the freezer too long and it's too cold (bitter loses all flavour if too cold). The correct technique is to keep the flame on the can at the liquid, and keep the liquid moving so there's no localised boiling.
What I did wrong here, was try to speed up the operation, by putting the can down and blasting it with the torch upturned a bit, which makes it spit gas and gives a bigger flame, which doesn't burn as hot, but spreads out, so less concentrated heat, which engulfed the can. I think what caused this was the heat hitting the dry part of the can, if there was some foam in there, that could have boiled pretty damn quickly and the seal of the can bust.
God it was loud, my ears are still ringing.
The beer in question is going down a treat though. :)