Sadly, my fridge is sans beer so I can't test this out yet but BeerBuddy.ca
claims you can punch in the bottling code on your beer and it will tell
you if it is fresh or rancid (I took some literary license here since
their web site was images and I couldn't quote their text by
Remember folks: if in doubt, buy beer that is fresh and drink it
shortly thereafter. Also, we don't suggest buying beer that has a code
to tell you when it expires, but that's just the way we are.
Link via: DoubleViking