People often tap the top of coke cans to stop them foaming over like this:

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Is there any evidence to suggest that tapping the top stops this happening?

  • I thought the idea was that tapping the sides of the can made any bubbles stuck there float up to the top. That way they don't push the soda up out of the can when you open it. I would imagine tapping the top would not be as effective. – M. Dudley Apr 21 '11 at 2:05
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    I can't believe I just went to ask this question and it was already here! +1 – Billy ONeal Jun 24 '11 at 15:36
  • Related question: skeptics.stackexchange.com/questions/6246/… – Oddthinking Nov 18 '12 at 13:04

Actually, the answer to this is simpler than that. I learned it from Penn & Teller's book How To Play In Traffic. On pages 76 to 86 they describe a trick you can play on your friends called "I Am The God of Carbonation". They have also done this trick on talk shows. They credit the idea for the trick to Paul Harris (and Eric Mead) in the magic book The Art of Astonishment.

The trick is immaterial to the answer, but it involves agitating one can as much as possible and then claiming you can transfer the carbonation energy from one can to the other. But what it hinges on is this:

I guess they've changed the way they package soda or something. No matter how hard you shake a soda can it takes only about twenty seconds for it to completely calm down....

As long as your God of Carbonation ritual takes twenty seconds or more, the shaken can will not explode. Make sure you hold the can straight up, perpendicular to the ground, and open it all the way with one quick action. That'll get rid of any little bit of fizz that didn't calm down in the twenty seconds.

The answer is that the tapping constitutes a ritual that just eats up time. As long as the can is sitting in an upright position and you wait long enough, the fizzing will die down.

  • According to the Snopes article the can that they tapped did have "slightly less foam" than the can that they didn't tap (but waited an equal amount of time for), so tapping seems to do something (albeit as a minor effect), not just eats up time. – jamesdlin Jun 6 '17 at 20:59

Snopes has already tackled this. They concluded it was FALSE, tapping made no difference.

  • Unless I am misreading, the Snopes article did say that tapping made the can foam (slightly) less but that it still overflowed. – jamesdlin Jun 6 '17 at 20:56
  • Think of the bubbles that collect on the inside along the walls and how tapping frees them to be above the liquid. – Muze the good Troll. Oct 31 '18 at 20:59

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