I recently figured out the "secret" code stamped on beer revealing the date in which the beer was brewed. This of course is only relevant to unpasteurized beer. Pasteurized beer should stay "fresh" for several years. The cans of Molson Canadian I found in my golf bag from the previous year for instance tasted lovely.
A = January, B = February, C = March and so on and so on. However there is no "I" therefore December is M.
Next time you're shopping for a box of unpasteurized beer, you might want to check and see when it was brewed. Lagers stay fresh for about four months and darker beer about five months. Beer like food is a perishable product where bacteria begins to form after a certain amount of time. It's just not regulated like food is.
I am sure we have all had skunky beer before and you can surely name the usual suspects. Corona, Heineken, Steinlager. Well, these beers for example must travel a long way to get here, hopefully in a refrigerated shipping container and who knows how long the beer was sitting in customs.
Stay thirsty my friends.