People tap the top or side of a bottle or can before opening it because they believe it prevents the drink from fizzing over. The idea is that tapping dislodges bubbles clinging to the inside walls, letting them float to the top where they can escape harmlessly. It’s one of those habits passed down so universally that most people never question whether it actually works. A 2019 randomized controlled trial put it to the test, and the answer is surprisingly clear: tapping doesn’t help.
What Causes a Drink to Fizz Over
Carbonated drinks are bottled under pressure, which forces carbon dioxide to dissolve into the liquid. As long as the container stays sealed and still, the CO2 remains dissolved. When you shake a can or bottle, tiny bubbles form and stick to imperfections on the inner surface of the container. These imperfections are called nucleation sites, and they can be remarkably small. Studies of bubble formation in carbonated beverages have estimated that active nucleation sites can be as small as 1 to 3 micrometers, far too tiny to see with the naked eye.
When you crack open a shaken container, the pressure drops instantly. All those tiny bubbles stuck to the walls rapidly expand and rise, dragging liquid with them. The result is the foamy eruption you’re trying to avoid. The intensity depends on several factors: how much CO2 is dissolved in the drink, the temperature of the liquid (colder drinks hold gas better and foam less), and how vigorously the container was shaken.
The Theory Behind Tapping
The logic sounds reasonable. If bubbles are clinging to the walls of the can, tapping should knock them loose. Once freed, they float up through the liquid and collect in the headspace at the top of the container, the small air gap between the liquid and the lid. When you open the can, that gas escapes without pulling liquid along with it. No mess.
This is the explanation you’ll hear from most people who swear by the habit. And the physics of it isn’t completely wrong. Bubbles do cling to container walls, and dislodging them before opening would, in theory, reduce the explosive release of gas. The problem is that tapping a few times with your finger doesn’t generate nearly enough force to dislodge the bubbles that matter.
What the Research Actually Found
In 2019, researchers conducted a proper randomized controlled trial, published with the straightforward title “To beer or not to beer: does tapping beer cans prevent beer loss?” They shook cans of beer under controlled conditions, then either tapped them or left them alone before opening. They measured the mass of beer lost to foaming with precise scales.
The results were unambiguous. For shaken cans, the average difference between tapped and untapped was just 0.159 grams, a quantity so small it wasn’t statistically significant. For unshaken cans, tapping made no difference either. The researchers concluded that tapping shaken beer cans does not prevent beer loss when the container is opened.
So why does tapping sometimes seem to work? Probably because of the few seconds it takes to do it. Even a brief pause gives some bubbles time to dissolve back into the liquid on their own. The tapping itself isn’t what helps. The waiting is.
What Actually Prevents Foaming
If tapping is a myth, what can you do instead? The most reliable method is simply waiting. In an unopened container, the high internal pressure works in your favor. Without any new energy being added, that pressure gradually pops the tiny bubbles and forces CO2 back into solution. An hour is more than enough for a shaken can to fully settle. Even 30 seconds to a minute of patience after shaking makes a noticeable difference.
Temperature matters too. CO2 is more soluble in cold liquid, meaning it stays dissolved more readily. A warm can of soda that’s been shaken is far more likely to erupt than a cold one that took the same beating. If you suspect a drink has been jostled, putting it back in the fridge for a few minutes helps on two fronts: it cools the liquid and gives time for the bubbles to settle.
Opening the container very slowly also works. If you can release the pressure gradually rather than all at once, you give the gas time to escape without violently expanding every bubble at the surface. With a screw-top bottle, this is easy. With a can, it’s trickier, but gently lifting the tab just enough to hear a slow hiss before fully opening can reduce the mess.
Why the Habit Persists
Tapping a can before opening it costs nothing and takes almost no effort. Even if it doesn’t work, there’s no penalty for doing it. That combination makes it the perfect superstition. You tap, you wait a couple of seconds, you open the can, and it doesn’t explode. You credit the tapping rather than the brief pause. Confirmation bias keeps the ritual alive because the few times a tapped can does foam over, you assume you didn’t tap enough rather than questioning the method itself.
There’s also a social component. The habit is so widespread that not tapping feels reckless, like tempting fate. It’s become a small, shared ritual, something people do automatically the way they might blow on dice or knock on wood. The gesture feels satisfying even if the physics doesn’t back it up.