The Science of Fizz: Does Tapping a Soda Can Really Work?

We’ve all been there. You grab a soda from the vending machine, and it tumbles to the bottom. Or maybe you drop a can on your way home from the store. You know that opening it right away means a sticky explosion. But then you remember the old trick: tap the top of the can a few times. Does this simple action actually prevent a fizzy disaster? Let’s decode the science behind the fizz and find out the truth.

Understanding the Pressure Inside a Soda Can

Before we can understand why a can might explode, we need to know what’s happening inside a calm, unopened can of soda. The fizz and bubbles in your favorite drink come from carbon dioxide (CO2) gas. During the manufacturing process, a specific amount of CO2 is dissolved into the liquid under very high pressure. This process is governed by a scientific principle known as Henry’s Law, which states that the amount of a gas that can be dissolved in a liquid is directly proportional to the pressure of that gas above the liquid.

Inside a sealed can, the liquid and the small pocket of air at the top (called the headspace) are in a state of equilibrium. The high pressure keeps the vast majority of the CO2 gas molecules happily dissolved within the liquid. When you open the can, you hear that familiar psssst sound. That’s the sound of the high-pressure gas inside the can escaping and equalizing with the lower atmospheric pressure outside. As the pressure drops, the dissolved CO2 starts to come out of the solution, forming the bubbles we love. In a calm can, this process is slow and controlled.

What Really Happens When You Shake a Can?

A common misconception is that shaking a can creates more pressure. This isn’t true. The amount of CO2 gas inside the can is fixed, so the overall pressure doesn’t increase. What changes is the location and state of the gas.

When you shake a can of soda, you are doing two important things:

1. Breaking Up the Headspace: You violently mix the pocket of gas at the top into the liquid, breaking it down into millions of microscopic bubbles.
2. Creating Nucleation Sites: These tiny bubbles get stuck to the sides and bottom of the can’s interior. The inner surface of an aluminum can is not perfectly smooth; it has microscopic imperfections. These imperfections, along with the newly introduced micro-bubbles, act as “nucleation sites.” Think of them as starting points where the dissolved CO2 can rapidly turn back into gas bubbles.

When you open a shaken can, the sudden drop in pressure causes the dissolved CO2 to rush out of the solution. Because there are countless nucleation sites all over the inside of the can, bubbles form everywhere at once. These bubbles expand rapidly and rise, pushing the liquid out of the can with them. The result is a messy, fizzy volcano.

The Tapping Theory: Does It Dislodge the Bubbles?

This brings us to the popular life hack: tapping the can. The theory behind this is that the vibrations from tapping the can’s lid or sides will dislodge the tiny CO2 bubbles that are clinging to the inner walls. Once freed, these bubbles are buoyant and will float up to the top, rejoining the larger pocket of gas in the headspace.

By moving the bubbles from the liquid back to the top, you are theoretically removing the nucleation sites. When you open the can, the CO2 will still come out of the solution, but it will do so from the surface of the liquid in a much more controlled manner, rather than from all sides at once.

So, does it actually work? The answer is a bit complicated. Tapping does, in fact, dislodge some of the bubbles. You can sometimes see them rising if you are using a clear plastic bottle. However, its effectiveness is minimal, especially for a can that has been seriously agitated. The vibrations are often not strong or consistent enough to free all, or even most, of the microscopic bubbles clinging to the can’s interior.

The Verdict: A Mostly Busted Myth

While the idea behind tapping is based on sound scientific principles, its real-world application is largely ineffective. Many experiments, including those by popular science shows and university physics departments, have concluded that tapping a can makes little to no difference in preventing a fizz-over.

The far more effective method is something much simpler: patience.

If you let a shaken can sit undisturbed for a few minutes, the same process that tapping tries to achieve happens naturally and much more effectively. The tiny bubbles will eventually detach from the sides on their own and float to the top, allowing the system to return to a stable equilibrium. Time is the true secret to preventing a soda explosion.

The Best Way to Open a Shaken Can

So, what should you do the next time you drop a can of Coca-Cola or LaCroix?

1. Wait: This is the most important step. Let the can sit upright on a flat surface for at least a few minutes. The more it was shaken, the longer you should wait.
2. Chill It: If possible, put the can in the refrigerator. Colder liquids can hold more dissolved CO2 (this is why a warm soda always seems fizzier). Chilling the can will make the CO2 less likely to escape violently.
3. Open Slowly: When you do open the can, crack the seal very slowly. This allows the pressure to release gradually, giving the CO2 more time to escape without forcing the liquid out with it. If you hear an aggressive fizzing, pause for a moment before opening it further.

Frequently Asked Questions

Why does warm soda seem to fizz more than cold soda? The solubility of carbon dioxide in water decreases as the temperature increases. This means a warm soda cannot hold onto its dissolved CO2 as well as a cold one. When you open a warm can, the gas escapes from the liquid much more rapidly and aggressively, creating a bigger fizz.

How long should I wait before opening a shaken can? There is no exact time, as it depends on how much the can was shaken. For a simple drop from waist height, waiting for 2 to 5 minutes is usually sufficient. If it was shaken vigorously, you might want to wait longer.

Does this science apply to other carbonated drinks like beer or sparkling water? Yes, absolutely. The physics of dissolved carbon dioxide under pressure is the same for all carbonated beverages. Whether it’s a can of beer, a bottle of champagne, or a sparkling water, the best way to calm it down after it’s been agitated is to let it rest.