Why Is My Beer Can Bulging? (Is It Safe To Drink)

Few things are as disappointing as looking forward to cracking open a cold beer, only to find that the bottom of the can is bulging. This common occurrence is surprising to many beer drinkers so you may be wondering if it’s still safe to drink and what causes this bulging in the first place.

The most common cause of a beer can bulging is due to pressure buildup inside the can. This pressure could be caused by carbon dioxide gas that builds up if the beer has spoiled or continued fermenting. The gas has nowhere to escape, so it puts pressure on the can until it creates a bulge.

There are also a few other reasons such as the can being frozen or it has been stored at high temperatures.

I decided to take a closer look at this and other reasons why beer cans sometimes bulge and share what I found here. I’ll look at why it happens, what it means for the beer inside, plus what you should do if you encounter a bulging beer can. So grab a cold one and read on to learn more!

Why Is The Bottom Of My Beer Can Bulging?

It all comes down to carbonation. Sugars in beer are turned into alcohol and carbon dioxide (CO2) gas during the brewing process. This gas is what gives your beer its signature fizz. Some of that CO2 is released into the air before canning, but most of it remains trapped and keeps your beer carbonated.

However, sometimes too much CO2 can end up inside the can, eventually causing the pressure to increase and the bottom to bulge out. This could happen for a variety of reasons including storage at high temperatures, the contents going bad, fermentation still happening, or even a problem with the can itself.

Another common explanation for your can looking deformed is when it has been frozen at some point. This causes the beer inside the can to expand when it freezes, popping the container out in the process. The bulge then remains when your beer thaws. 

You can usually tell if this has happened as there will be some give in the sides of the can when you squeeze it. If you’re sure this is the cause (maybe because you did it!) then the beer will probably be ok to drink, but read below on how to check it just in case.

Another reason is that the beer has started fermenting again inside the can. This can be the result of poor standards at the brewery with the beer being packaged still containing active yeast or maybe some contaminants getting in, turning it bad.

The result of this is the beer undergoing a secondary fermentation leading to a change in the volume of alcohol and possible tainting with bacteria or other microorganisms.

It’s usually fairly easy to tell if this has happened once you’ve opened the beer.

A less common cause of a bulging beer can is being stored at high temperatures, as this may result in an excess of CO2 buildup. But unless the can only became distorted after you had purchased it, then it’s impossible to know if this was the case.

Check the section below for easy ways to tell if it’s still ok.

Is It Safe To Drink A Bulging Beer Can?

If the bulge is small and the can feels firm but not rock hard to the touch, it may be safe to open and drink. But, if it’s larger than a golf ball, it’s best to dispose of it.

If the sides of the can have some give when you squeeze it then you can be sure there is not too much pressure build up in the can and it will be ok to open so you can check the contents.

To start with, remember that a swollen beer can does not always indicate danger, but it is wise to be careful and check if the can is safe to open in the first place, just in case. Beer cans are made to withstand a lot of pressure which is going to get released the moment you open them.

As I mentioned above, a bulging beer can is often a sign of too much carbon dioxide (CO2) gas building up inside. While a small bulge may not be a problem, a can that is severely distorted could indicate that the pressure inside has become dangerous.

A word of warning though. It may be best not to keep hold of an inflated can for too long. If the pressure inside the can continues to increase, it could potentially burst, causing a mess and even injuring someone in the process.

See my checklist below to tell if a beer is still good to drink or not.

How Do You Know If A Beer Can Is Undrinkable?

If you’re determined to check out the beer to see if it’s still drinkable then cautiously open it and pour the contents into a glass. Then check the following:

  1. Does it have a strange smell? Give it a sniff to see if it smells strange or unpleasant as that’s a good indicator it’s gone bad.
  2. Does it look right? If it’s gone cloudy or has a different color than usual it will probably be spoiled.
  3. Does it taste off? If it looks and smells ok then take a small sip of the beer to see if it tastes funny or sour. If it does, then it may be spoiled or contaminated.

First of all, my mantra is always that it’s better to be safe than sorry when it comes to food and drink safety.

Unless you know the cause of your beer can looking weird (such as freezing it) then I would just dispose of it carefully.

If it fails any of these tests then tip the beer down the drain and open a fresh one.

Can You Get Botulism From Beer Cans?

It’s very unlikely you could get botulism from a beer can as it’s caused by a toxin from the Clostridium botulinum bacteria which does not usually thrive in beer cans.

The main reason for this is that beer is acidic, contains alcohol, and is usually pasteurized to kill any bacteria. Essentially, most beer cans do not provide the right environment for botulinum toxin production.

The toxin growth is delayed at 4% alcohol strength and completely inhibited at 6% and the World Health Organization states the toxin doesn’t grow in a pH below 4.6. Beer varies between types but is usually moderately acidic somewhere between 3-6 on the pH scale.

Botulism is also very rare with only an average of 145 people a year getting it in the USA.

That being said, the toxin is extremely dangerous so if you’re worried about getting botulism from your beer can because it’s damaged in some way then just throw it away.

Dented Cans Vs Bulging Cans

As we now know, a bulging can is caused by the buildup of pressure inside in some way and there are various reasons for this which I’ve already explored.

But what about if the beer can is just dented. This usually comes from dropping the can which causes damage but are these cans still safe to drink?

The key thing is to check the can over and look for any signs of leakage. If there is then just toss it in the garbage straight away as it’s been exposed to air and contamination.

Check out my article on whether a dented beer can is safe to drink for the full details.

As long as the container is still sealed and airtight then it should be ok to consume but see above how to check the beer first to make sure it hasn’t gone off.

If the beer is flat that is a clear indicator as the CO2 gas has been allowed to escape.


I hope you’ve found this article useful and you now know all about the causes of bulging beer cans.

Just remember that even though the beverage may well still be ok to drink, it’s best to just discard it if you’re not sure.

Check the beer over carefully to see signs of spoilage.

Also, always take great care when opening a swollen beer can as it will probably make a mess at the very least.

Tom Hambly

Tom Hambly is the founder of Totally Drinks. He loves to cook and drink nice things - his favorite drinks are wine, beers and whiskey. About Tom Hambly.

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