The best before date on the bottles is the date up to which the brewer guarantees perfect quality. After this date, it is possible that the quality of the product will deteriorate. This is particularly noticeable in the flavour of the beer. How quickly this happens depends on a number of factors. When you store beer in a cool, dry place the flavour remains good for longer as opposed to storing it in a bright, warm place.
If beer is past its best before date, pour it into a glass and take a smell. If it smells musty, then the flavour of the beer won’t be good.