Some of the aromas, the flavors, and the oils that make up the great flavor of a fresh beer go away with an expired beer.
It simply loses flavor — generally a year after being opened. Fresh beer is always better to drink than old beer. But, the real reason for choosing if you want to drink it or not, is the "freshness" of the beer. So if you want to drink the old beer that’s been in the bottom of your refrigerator for a few year, go for it – at your own risk, of course. But beer is best enjoyed fresh. In fact, producers of those beers often recommend that they should be stored for at least a year or two before opening. Beer doesn’t expire in the sense that drinking it will make you sick. Beer doesn’t expire. The below beer is a fine specimen brewed by Rodenbach brewery in Belgium.
Beer really is a delicate product. Liquor does not expire to the point of causing sickness. No. Depending on the factors listed above, it will probably not taste as it was originally intended. As beer begins to age, it begins to change its flavor profile. If you look at the average beer can, bottle, or growler, you’ll find that there is an expiration date printed on the container. Does Craft Beer Expire? Most beers have expiration dates but most beers don’t “go bad” after their expiration date, rather, they change…not all for the better of course. As long as it is sealed then you can drink it years or even decades after it was brewed. That should allow the beer to age and get its distinguished taste.
Beer left in a can, under good ol American Canning regulations actually doesn't expire. Beers have started to print a "Born on" date or a "Guaranteed fresh" date on the can. There may also be a “born on” date that lets you know when the beer was bottled. Some breweries will have “born on” date or a “best by” date stamped on the bottles.
Because these dates are printed on the container, it means that beer technically does expire. Some vintage beers (ales, lambics or stouts) have high alcohol content and they are made to last a few years. It simply loses flavor — generally a year after being opened.