Why would an aged beer explode? I had a bottle of Westvleteren XII aging in my fridge. As I was putting some other bottles next to it, I nudged it slightly and the bottle shattered violently. I'm certain that I didn't hit it with enough force to do that kind of damage, so I'm thinking that there was pressure that had built up inside the bottle.

Is this something that's plausible? Could it mean that the beer had gone "off" and so I should not feel bad that my prized beer ended up as a sticky puddle?
I've been homebrewing and winemaking for almost 25 years and there are 3 reasons why a bottle might explode.


Too much sugar for the secondary fermentation in the bottle. Homebrewers do this ALL THE TIME. Turns your beer into little hand-grenades. Sometimes fermentation is not complete and with the normal addition of sugar at bottling can cause problems. This happens frequently in high gravity beers.
Infection - by this I mean something other than yeast was in the beer and started eating the sugar to make the carbonation in the beer. It could be a wide variety of agents from yeast to bacteria to fungus. They convert sugar to CO2 at different rates than yeast. Many times they produce more CO2 causing gushing beers and sometimes broken bottles.
Defective bottle. 99.99% of the time bottles are built to spec, but occasionally one slips through with a defect and many times that can lead to a bottle failing. Also, bottles are sometimes dropped or banged around causing a crack.