# Pressing Scientific Issue: Do Pump-Caps Preserve Soda Fizz?, Part II **URL:** \ **Category:** Factual Questions\ **Created:** [April 13, 2003, 3:28am UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380 "2003-04-13T03:28:22Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [October 15, 2011, 2:07pm UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/21 "2011-10-15T14:07:10Z")
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!) ---
**Author:** ![Channing\_Idaho\_Banks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/channing_idaho_banks/32/250_2.png) [@Channing\_Idaho\_Banks](https://boards.straightdope.com/u/Channing_Idaho_Banks)\ **Post date:** [November 20, 2016, 5:47pm UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/24 "2016-11-20T17:47:34Z")
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 ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [November 20, 2016, 6:44pm UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/25 "2016-11-20T18:44:44Z")
Click and Clack as a citation ??? How do I delete my account here? ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [November 20, 2016, 7:28pm UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/26 "2016-11-20T19:28:34Z")
> [@Measure\_for\_Measure](#): > > I was going to leave this for somebody with some chemical background, but since nobody has jumped in… > > The concentration of CO2 in the headspace of the bottle affects the equilibrium quantity of CO2 dissolved in the water. That’s consideration #1. > > The air pressure in the headspace (as well as the temperature of the liquid) affects the speed at which the system attains equilibrium. That’s consideration #2. The technical term for this appears to be, “the kinetics” and I suppose that it’s what you were referring to. But this is something that is relevant for hours, not days – or even 1 day according to measurements. See Squink’s older post for the science and my reference to Rohrig (2002) for the empirical observations. > > IANAC (I am not a chemist). Corrections and headsmacks are invited, as appropriate. 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. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [November 21, 2016, 12:52am UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/27 "2016-11-21T00:52:31Z")
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. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 21, 2016, 1:19am UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/28 "2016-11-21T01:19:00Z")
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? ---
**Author:** ![voltaire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voltaire/32/313_2.png) [@voltaire](https://boards.straightdope.com/u/voltaire)\ **Post date:** [November 21, 2016, 2:12am UTC](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380/29 "2016-11-21T02:12:46Z")
Some real _pop_ science happening here! [Previous page](https://boards.straightdope.com/t/pressing-scientific-issue-do-pump-caps-preserve-soda-fizz-part-ii/168380.md?page=1)