I can tell you, from observation before I had that soda dispenser mentioned in my last post, that my pop bottles would not reach equilibrium in only one day. They would be noticeably harder if they went two days without opening them again.
YMMV if you keep your bottles on the door. Then the extra jostling will tend to make it reach equilibrium faster. (So don’t do that!)
I’ll defer to Click and Clack the tappet brothers. I remember on car talk they did an experiment and figured out that the best way to conserve the CO2 in your soda bottle is to put the screw cap back on as fast as possible. They didn’t mention anything about squeezing the bottle
Click and Clack as a citation ???
How do I delete my account here?
Yeah, that’s pretty close to it. The carbon dioxide will come out of solution until it reaches equilibrium with the carbon dioxide in the headspace. The equilibrium concentration varies with the temperature and pressure. Pressurizing the headspace with air will not help retain carbonation because there isn’t enough CO2 in the air to have much of an effect. The pressure in the headspace will be the sum of the partial pressures of the gases in that headspace.
Simpler than a pump cap, would be a belt around the 2-liter bottle, with a shim that can be inserted between the belt and the bottle. Close the bottle tightly, slip in the shim, and tignten the belt to cave in the side of the plastic bottle. That will increase the pressure of the air inside, the same as a pump cap would, but much easier to fashion with relaxed tolerance for fitting adequately. A simple rubber gasket would also enable the cap to be replaced with a tight seal.
If a pump cap works, the shim-belt would work just as well.
I seem to recall reading/learning (somewhere) that a significant factor is the amount of space in the container not filled with liquid, which I gather is the headspace mentioned in some posts above. Thus squeezing a flexible bottle to get all the air out (but really for the purpose of not leaving much or any space for the CO2 to fill) or transferring to a smaller bottle with little or no headspace could be effective in minimizing loss of fizz, whereas simply adding air and pressure won’t help much. In other words, the way to preserve fizz is to reduce or eliminate space, not to increase pressure. Does this sound like an accurate summation of the issue?
Some real pop science happening here!