The short answer is yes, beer does expire. But to say that it has gone bad is a bit of a misnomer; it doesn't become unsafe to drink, it just starts to taste unpleasant or flat. Yes, its flavor will degrade over time. When it comes to beer, there are some general rules you can follow. According to the Approved Food Blog, standard strength options remain fresh for 6 months to 2 years after brewing.
Standard strength beers include pale ales, IPAs and lagers. Expired beer is completely safe to drink. It is harmless, non-toxic and perfectly safe to consume. It won't taste great, and it may smell strange and taste rancid. The taste of beer is more easily killed by oxidation than anything else.
It's not recommended to drink beer past its expiration date, but if you do consume a “rotten beer”, it shouldn't hurt you or make you sick. The practice of drinking beer that has passed its expiration date is not considered dangerous by experts. You can still buy a beer that is closer or beyond its expiration date, but you should be aware that it will have a shorter shelf life and that you should consume it soon. Oxidation is the chemical reaction that takes place when oxygen molecules interact with the molecules in beer and the other ingredients that give the drink its flavor. However, it is misleading to say that the beer has expired; it doesn't really become unsafe to drink; it just starts to taste flat and unattractive.
There is no danger in drinking expired beer; it is harmless and non-toxic. However, according to The Washington Post, there are no strict regulations or guidelines requiring breweries to test the date their products were packaged only the date they expire. You should never drink beer past its expiration date, but if you do consume an expired beer, you won't get hurt and you probably won't get sick. A good rule of thumb is to store beer at the same temperature, or a little warmer, than it would be drunk. For example, by barbarding Lambics, deliberately subjecting beer to oxidation at controlled temperatures can improve taste and elevate the overall beer drinking experience.
The thing about expired beer is that it keeps aging and changing inside the bottle over time, and those changes aren't always for the better. In conclusion, while expired beer isn't necessarily unsafe to drink, it's best not to take any chances with your health. If you're unsure about whether or not your beer has gone bad, it's best to err on the side of caution and discard it.