The beer will not be bad in the sense of unsafe to drink, since no harmful pathogens grow once the beer is fully fermented.
So you can certainly drink the beer.
However, the beer may not taste good!
Over time, the beer will oxidize, both from oxygen introduced during packaging, but also through the release of oxygen from compounds previously oxidized in the beer.
The oxygen causes the beer to stale, producing tones of sherry, paper, cardboard.
Hop aromas are muted, and hop beta acids oxidize to produce an unrefined bitterness.
Other forms of staling can lead to a soap taste.
Generally, the higher the alcohol content of the beer
the less you need to be concerned with the use by date.
beer.stackexchange.com/users/112/mdma
StillTasty.com has the following to say with regards to beer - particularly specifying that this applies to regular or light beer from bottles or cans manufactured by major breweries: Opened Containers Good for 1 day, refrigerated.
Tips: Keep refrigerated and tightly covered.
After opening, most commercially manufactured beer will remain safe to consume if properly stored, but it will quickly become flat and lose flavor.
Unopened Containers Good for 4-6 months, in pantry or refrigerator.
Tips: The precise answer to the question "How long does beer last?
" depends to a large extent on storage conditions - store beer in cool, dark area.
Keep beer away from direct sources of heat or light; too much exposure to light can cause beer to develop a foul taste.
To maximize the shelf life of beer, store beer at a temperature between 45° F and 55° F (colder than the typical room temperature, but warmer than a refrigerator) - if this is not possible, store beer in the refrigerator.
Storage times shown are for best quality only - after that, the beer's color or flavor may change, but in most cases, it will still be safe to consume if it has been stored properly.
How to tell if beer is bad?
If beer develops an off odor, flavor or appearance, it should be discarded for quality purposes.
"
Best By," "
Best if Used By," and "Use By" dates on commercially packaged foods sold in the United States represent the manufacturer's estimate of how long the product will remain at peak quality - in most cases, the beer will still be safe to consume after that date, as long as it has been stored properly and the package is not damaged.
Beer made by some micro-breweries may not retain peak quality as long as beer from major breweries.
beer.stackexchange.com/users/162/user162
This depends entirely on the beer.
As a rule of thumb I would say that any beer which is re-fermented once bottled, can be preserved for several years.
You need to be careful when preserving, but it's not unheard of to drink 35 year old beers.
Often these beers are the darker, stronger ones like Westmalle or Orval.
beer.stackexchange.com/users/138/Lucas Kauffman
This depends on many factors, but usually best-before date is what is states, also the date before which the full quality of the product is guaranteed.
It doesn't mean you can't consume it afterwards, it just means that you can't make formal complaint about the taste or potential sickness caused by consumption of the product after that date.
The people from food industry said me, that it is general rule, that the best-before date is normally exaggerated in bottom direction, just to protect the company from potential sues.
I've often drank beer much after best-before date, and as long as that date wasn't exceeded by more than a year, I haven't noticed any big difference in taste.
beer.stackexchange.com/users/21/Danubian Sailor
It should still be safe, taste good is a personal opinion.
Some beers age well, high alcohol, sours, and smoke beers.
Others don't age as well (hoppy beers).
Plus it all depends on how the beer was stored.
Out in a hot garage?
Sitting in your window sill?
beer.stackexchange.com/users/529/Wayne In Yak
Does beer really go bad after the 'best before'-date?    I hear I can drink beer even after the expiration date, but is it safe and does it still taste good?
Does beer really go bad after the 'best before'-date?
beer.stackexchange.com
<taste><health><preservation>
beer.stackexchange.com/questions/195
beer.stackexchange.com/users/138/Lucas Kauffman
Beer can be drunk after the best before date as long as it has not been opened. Over time, however, the quality will decrease, e.g. taste, but it will still be safe to consume. Best before date protects the manufacturer as you cannot make claims after that date if you drink the beer and you get sick.  This will depend on the type of beer and the manufacturing techniques, but beer is usually safe to drink well after the best before date, which is often a very conservative estimate of its quality and not an indication of whether it is safe. The beer should be discarded if it tastes off, but in most cases it just develops a taste that may not be as pleasant.
This will depend on the type of beer and the manufacturing techniques, but beer is usually safe to drink well after the best before date, which is often a very conservative estimate of its quality and not an indication of whether it is safe. The beer should be discarded if it tastes off, but in most cases it just develops a taste that may not be as pleasant.