Does Tapping the Side of a Beer Can Actually Reduce the Fizz?

A shaken can of beer is an accident waiting to happen. Mariyana M/Shutterstock

The long and storied history of beer is rife with colorful traditions.

Canned beer — a relatively modern development — doesn't enjoy that kind of history. But there's one custom that's been around since the first can of suds hit store shelves in 1935.

That's the traditional tap on the side of the can — believed to prevent all that fizz from erupting when you open it.

The trouble is, no one has actually taken the time to confirm if it actually works. Sure, you might have gotten fizz on your chin once or twice, even after tapping. But who's to say that tap didn't save you from an even worse fate — an entire face-full of beer?

Beer drinkers, on the whole, may not pay that much attention to the issue.

There's at least some theoretical basis for the tap. As MIT Technology Review notes, a tap should free up bubbles that may cling to the inner wall of a can. Once those bubbles float to the top of the can, they dissipate politely. Most importantly, no one should get wet.

That reasoning may be good enough for most beer drinkers, but scientists tend not to let these things slide.

So researchers at the University of Southern Denmark set out to determine if that tap actually eased the volatile nature of canned beer. Especially after a can has been shaken, priming all those tiny bubbles from the carbonation process for an explosion.

SPOILER ALERT: It doesn't.

But it's worth raising a glass to the researchers for their remarkable dedication to the experiment. For their study, published this month in the journal arXiv, they tested the tap theory on no less than 1,000 cans of beer.

"Given the strong Danish tradition in beer brewing and consumption, we set out to settle this matter with high-quality evidence," the researchers explained to MIT Technology Review.

Top of beer can with foam spilling over.
Scientists were rightfully concerned about beer spillage. PixieMe

No, they didn't drink all that beer themselves. Staff and students at the university were invited to partake. For their experiment, researchers divided the cans into two groups: shaken and not shaken.

The former were particularly abused, getting swished around by a machine at 440 rpm for a full two minutes. The researchers say that's about equal to being carried on a bicycle for 10 minutes.

Once those cans were all fired up, researchers gave them a few taps. The beer testers weren't told which cans were potential fizz bombs. But those shaken cans did erupt as expected, losing about 3.45 grams of beer upon being opened. Not surprisingly, the unshaken cans lost much less beer, at around half a gram.

And those three taps? They didn't make any difference on how much fizz spilled over, shaken or unshaken.

Researchers aren't exactly sure why the tap method failed. But they suspect barley proteins may keep the bubbles from rising to the top of the can and dissipating. For that, a much harder tap may be required. But then, of course, you might be dangerously close to making those bubbles angry those bubbles — and getting a face-full of foam.

If at all possible, the scientists suggest, it's best to simply wait and let those bubbles calm down on their own.

It's also worth noting, as the video below shows, that explosive foam isn't just a problem for canned beer. Bottles may get even more worked up if you tap them.