I’ve just opened a month old bottle of beer and when I popped the cap it made a BANG

, akin to the noise a champagne cork makes but louder.
Once I’d regained my composure, checked for snipers and realised I really needed this beer now I noticed the beer wasn’t overflowing out of the top like you’d expect after such an explosion.
Now I’ve opened a few beers in my time and haven’t experienced this phenomenon before. Is it that unusual?
I’m now plucking up the courage to open another. Perhaps the more I drink the fear will diminish?