# Why are coke bottles that much fizzier if you shake them?

We've all been there: you drop your bottle of soda at some point and when you try to open it, it bursts into foam.

My question is, then: why does shaking a carbonated drink make the dissolved gas escape?

(I can't think of appropriate tags for this so feel free to retag.)

Although Why can't CO$_2$ mix back with the liquid after a soda bottle has been shaken? is a duplicate to this question, I'm not sure it's a great answer and it would be good if someone could come up with a better answer here.

The accepted wisdom is that shaking the bottle creates tiny bubbles and these act as nuclei for bubble formation when the pressure is released. Without these nuclei bubble formation is mostly by heterogenous nucleation on the bottle walls, and that is slower.

However I have never seen a paper that demonstrated this is the case, for example by light scattering measurements on the shaken but unopened bottle. The nearest I've seen is this paper, which seems reasonably authoritative though it's not from a peer reviewed journal. If anyone knows of such papers, or feels like doing the experiment, I'd be interested to see the data.

It is known that the pressure isn't increased by shaking/dropping the bottle (the article I linked measured this) so some form of enhanced nucleation does seem the most plausible mechanism. It's just that it would be nice to see it proved.

• Nucleation is obviously right, do you really need light scattering formal experiment to be persuaded? You can see the little bubbles form in the soda with your eyes. The sound waves from an impact or turbulent shaking make lots of little low-pressure regions that nucleate gas, and these millions of little bubbles nucleate when you open. – Ron Maimon Jul 18 '12 at 16:58
• I have just deliberately dropped a bottle of lemonade, and while I could see some large bubbles immediately after the drop, after a minute or two I couldn't see any bubbles in the bulk of the lemonade. Although I didn't sacrifice this particular bottle, experience tells me that a dropped bottle will foam vigorously if opened ten minutes after dropping. I'm not doubting that nucleation is the mechanism, but from a casual inspection I can see no experimental evidence for it. – John Rennie Jul 18 '12 at 17:03
• When I drop cola, I see little white dots in the soda for a minute or two. The lemonade might be too bright to see the light-scattering. The bubbles have to re-dissolve, it will take a while (I don't think as long as 10 min., maybe 3). – Ron Maimon Jul 18 '12 at 17:18
• Bearing in mind I used to be a colloid scientist, and am very used to using light scattering to see what's floating about in suspension, it seems an obvious and easy experiment to do. It should be straightforward to watch the bubbles appear then redissolve after some suitable disturbance. You could even track bubble growth (the initial stages at least) as the pressure is released. Sadly I no longer have access to that sort of kit and I doubt my former employers would see it as a good use of ther shareholder's money :-) – John Rennie Jul 18 '12 at 17:29
• In my experience, the bottle does feel like the pressure increases when I shake it. It does seem like it's worth a few hours of my time (and some off-hours lab equipment) to do this experiment properly. Hmmmmm.... – Floris Aug 30 '14 at 14:47

Think of this in terms of Le Chatelier's Principle.

An unshaken bottle should be in a state approaching thermodynamic equilibrium of concentration, temperature, volume, and partial pressure. The rates of the chemical reaction describing solution of the CO2 components is equal in both the solution and the dissolution directions.

When you shake the bottle, you mix it and speed up the reaction in the direction of solution. (Just like you can speed the dissolution of sugar in tea by stirring.) This causes the liquid to become super-saturated with respect to the CO2 component. Uncork the bottle and pressure of the gas is suddenly lowered and the super-saturated solution boils. Super-saturation is a metastable state.

As a test of this hypothesis, I also think you would find shaking a closed bottle of pop will slightly lower the temperature and slightly lower the pressure of gas and slightly change the volume of liquid.

• This seems to argue in the opposite direction of observation: the pressure in the gas goes up when you shake the bottle, not down. You can feel a plastic bottle become "tight" when you shake it. – Floris Aug 30 '14 at 14:46
• @Floris: Does it? If it does that means something else has to change, according to the ideal gas law: the volume, temperature, or density. So it doesn't. Pressure doesn't actually change, and shouldn't. In fact, school experiments routinely shows this case. – Pwnna Nov 14 '14 at 0:45