Beer Expiration

Beer expiration issue?
What if you bought beer and refrigerated for 2-3 weeks then just left stored in a cupboard for two weeks, how bacteria grows a kind of strange or is still good to drink? oh yeah, and just add, for some strange why my friend moved from its container to a container a water bottle, so it has been opened before, but their storage in a dark area.
Unlike fine wine, you have no worry about without opening the beer … if a generic or a wonderful beer last month, okay. In fact, have a beer cold on me!
ShikixIchijou [My mep part] Can you see me now