http://www.snopes.com/science/sodacan.asp
When I was younger, I was told that to prevent a soda from fizzing over when you opened the can, you should tap the top of your can a few times. Ever since then, I've tapped the top of my soda can every single time I've opened one; it has become a habit. After doing some research for this blog post, I found this entry stating that the entire thing is a myth, and that tapping your soda can before you open it actually makes no difference in the amount of fizz that comes out. Because fizz is created by forcing carbon dioxide and water together under pressure, an un-opened can of soda is nearly fizz-free because the high pressure inside the can forces the carbon dioxide to stay within the liquid in the can. The pressure is reduced when the can is opened, and it is this event that creates the fizz in the can. Shaking a can of soda creates bubbles within the liquid and breaks the bond between the carbon dioxide from the liquid in the can; therefore, there is more pressure and more carbon dioxide looking to separate from the liquid which causes an explosion of fizz when you open a can.
After hearing that tapping the can does nothing to prevent fizz, and seeing the experiment that the people from the website did to prove this. I decided to try it for myself. I took three cans of Diet Coke, shook each one vigorously for 5 seconds, and then opened each one differently. For the first can, I opened it immediately after shaking it; the soda sprayed out of the can and fizzed over the top. For the second can, I let it sit for ten seconds and then opened the can. Rather than spraying into the air, the fizz simply just came up and overflowed out of the can. For the third can, I tapped the top of the can for ten seconds and then opened it, obtaining the same results as I had for the second trial: the fizz came up and overflowed out of the can the same way it had after letting it sit for ten seconds.
After doing the experiment for myself, I have to admit that I was slightly surprised that tapping the can really did have no effect on the fizz within the can; I have been doing it for as long as I can remember! As with many things, the fizz dies down with time, so next time I grab a can of soda, I'll just have to let it sit for a few seconds before trying to open it.
