Does Tapping a Soda Can Prevent it from Foaming Over?

(Image credit: morguefile.com)

They say you can’t un-break what’s broken, un-see what you’ve seen or put the toothpaste back in the tube. But can you un-shake a can of soda?

Well, that depends: How patient are you feeling? Just as time heals all wounds, it also bursts all bubbles, from the Mississippi bubble to the housing bubble to the bubbles in your soda can. Heck, given enough time, entropy will pop every bubble in the universe.

The problem is, we humans are a controlling, impatient lot. As kids, we try to will the school clock to turn faster and cajole our parents to let us open our presents early; as adults, we turn our attention to yelling at stop lights, honking in traffic and habitually tapping pop and beer cans. But, as much as we might cleave to our urban myths and superstations for the sense of control they give us, this effervescent anecdote doesn’t hold water.

Carbonated soda consists of carbon dioxide dissolved in a liquid. Inside a sealed can, interior pressure prevents gas from escaping the liquid (much the same way that altitude and atmospheric pressure affect the boiling point of water). Crack it open and some CO2 gas escapes; pour it out and more gas escapes, foaming into the characteristic, nose-tickling head.

When you shake a can of soda, you add energy to the system, which enables bubbles to form – usually along tiny imperfections on the sides and bottom of the can. Like a beach ball held under water, these bubbles will exit the liquid quickly and violently once pressure is released, shooting out so fast that they carry a stream of liquid along with them.

Some people think tapping the sides or top of the can will break up the bubbles but, according to an article on Chow.com, representatives from both Coke and Pepsi agree that the tapping method does not work. In fact, by adding energy to the system, you stand a chance of generating more bubbles. Experiments at myth-busting website Snopes.com agree.

Some sources claim that results vary according to soda type.

Ultimately, any evaluation of the tapping method suffers from the fact that, while you tap, time keeps on slipping, slipping, slipping into the future; for all you know, it’s time, not tapping, that bursts the bubbles. Still, that doesn’t mean you’re completely powerless. Since the solubility of a gas is a function of temperature and pressure, you might be able to speed things up by cooling the can down in the fridge or (briefly) in the freezer.