Pressing Scientific Issue: Do Pump-Caps Preserve Soda Fizz?, Part II

There is a device called Fizz-Keeper, which allows the user to pump compressed air into soda bottles, thereby allegedly “preserving the fizz”. I am curious about this item’s effectiveness.

A recent thread discussed this issue; I would like further details.

(1) There are anecdotal accounts (including my own) that the fizz-keeper does indeed work. It is not necessary to add further casual observations. (I will not object if someone wants to bump this thread from page 3 though. :wink: )

(1a) Going beyond mere impressionism, if somebody wanted to test one of these devices, how would the fizziness be measured? Could it be measured using ordinary household items?

(2) The aforementioned thread and this website suggests that the Fizz-keeper should not work, since “the escaping gas can be pushed back into the liquid only by forcing more molecules of that particular gas (in this case carbon dioxide) into the space above the liquid.”

(2a): Just to clarify: if you pumped pure oxygen at 100 atmospheres into a soda bottle’s headspace, this would have no effect on the liquid’s long run ability to carry CO2, right?

(2c): I understand that the amount of CO2 in ordinary air is inconsequential.

(3) The Journal of Chemical Education (Howald, Reed. The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics J. Chem. Educ. 1999 76 208. ) claims the following:

I’d like a little elaboration on this point. Does “hours” mean 2 hours, 48 hours or what? No WAGs needed. And why the heck would the kinetics be affected? (And what does that mean anyway?)

(3a) Regarding kinetics, how many times should the Fizz-keeper be pumped?

(4) Bonus question: Why is CO2 used to make soda fizzy, rather than any other gas? (Hmmm. Helium might be diverting.)

To summarize, I want to know whether the Fizz-keeper really works, and I want the answer to be scientific, Gaad dang it. :slight_smile:

Disclaimer: I lack a background in chemistry or physics, so I won’t be able to moderate this thread very well.

once the seal is broken on a bottle or a can of soda (doesn’t matter) the “fizz” begins to escape. Even if you pump air into the bottle or can, the container will not be able to hold the pressure because the seal was broken. The compressed air will escape, and the “fizz” will escape a little later.

(4) Why CO[sub]2[/sub] ?
CO[sub]2[/sub] is a good choice for making fizzy drinks, because not only does it dissolve in a liquid, like other gases, but also reacts with water to form carbonic acid, and its ions. Thus the equilibrium concentration of CO[sub]2[/sub] in the air ,vs solution, lies towards more total carbonates in solution than with a ideal, nonreactive gas. If you charged a bottle of Soda with helium, rather than CO[sub]2[/sub], most of the gas would come out in one great bump immediately upon opening. However, the kinetics of CO[sub]2[/sub] <->HCO[sub]3[/sub][sup]-[/sup] <->CO[sub]3[/sub][sup]2-[/sup] are slow (~seconds), so not only do you end up with a lot more potential gas dissolved when you use CO[sub]2[/sub], but it comes out more slowly.

The CO[sub]2[/sub] <->HCO[sub]3[/sub][sup]-[/sup] <->CO[sub]3[/sub][sup]2-[/sup] equilibrium depends on temperature, pH, and yes, pressure. Data on the pressure effect is hard to come by, however before the last thread on this subject crashed-and-burned, I did find a site that gave a few figures. Can’t locate it now, but it’s a small, nonzero, effect.

With plastic bottles at least, there may be a simple explanation for why some the pump seems to work for some people:
The soda pop is supersaturated with respect to CO[sub]2[/sub] (all those carbonates…).
The bottle is flexible.
When you close the bottle you tend to squeeze it.
This results in a low initial air-pressure inside the bottle, and walls that are easy for increased pressure to deflect.
Since the pop is supersaturated, carbon dioxide gas will come out of solution, until the point where the walls of the container supply enough rigidity for pressure to build and stop the process.
Using a pump lets you use air, rather than fizz to make the container rigid.

If that’s not too clear, think about what would happen if you quickly pulled a vacuum on a soda bottle, and then sealed it. You’d end up with a normally inflated bottle with a pressurized atmosphere of nearly pure CO[sub]2[/sub] above the pop. - Flat soda.

Terrific post, Squink.

To Recap

To the extent that bottle rigidity is the goal, it appears that one or two pumps should be sufficient.

Another method of promoting fizz duration is to keep the bottle well chilled, as Squink and one of my links pointed out.

We are still left with a strictly empirical question: does the fizz-keeper really work in a meaningful way? For example, how does it compare with efforts to keep the beverage well-chilled?

Methodological Concerns
Looking over Squink’s links, it appears that H[sub]2[/sub]CO[sub]3[/sub] is a weak acid (carbonic acid), so a precise ph measurement, might proxy for fizziness. But perhaps there are better methods.

An interesting aside, Guneiss Stout (Beer) uses nitrogen as well as the natural fermenting CO2.

I think the reason we use CO2 is because the fermenting process produced it, when we figured that out we could carbonate any beverage.

Suppose that we put high-pressure air into the bottle, along with the pop. Presumably, that would then force some nitrogen and oxygen into solution, as well, would it not? And any gas in solution would “fizz” when the bottle is opened, correct? So if these pumps increase total gas concentration, does it really matter whether the gas is CO[sub]2[/sub]?

As an aside, I’ve also seen gizmos which take a small compressed CO[sub]2[/sub] tank, like you might use for a BB gun, and carbonate or recarbonate drinks, and those would obviously increase CO[sub]2[/sub] solution, but that’s not what the OP is asking about.

Ok, Chronos, but Squink claims that CO2 and H2O forms carbonic acid, which allows the beverage to stay fizzy for more than a few seconds.[sup]1[/sup] So the effects of lightly pressurized Nitrogen and Oxygen should be shortlived and (I would guess) small.

Admittedly, O2 and Nitrogen are more reactive than helium and kanicbird implies that Nitrogen reacts with stout in some way (though I speculate that it does not react that much with water).[sup]2[/sup]

I’m curious about those CO2 gizmos. I wonder whether they are cost-effective.

[sup]1[/sup][sub]flowbark disavows any knowledge of chemistry.[/sub]

[sup]2[/sup][sub]Ha! I knew Guiness had a different mouthfeel than other carbonated beverage products![/sub]

Update! Update! Update! Update! Update! Update! Update! Update! Update! Update!

Wikipedia has a decent treatment of the issue:

Although Fizz Keeper affects the kinetics the effect lasts hours, not days. Plus, Rohrig (2002) notes that the seal of an ordinary cap is better than that of Fizz Keeper. As a result, ordinary caps tend to beat the Fizz Keeper over a 24 hour period. Experimentally.

If you want to extend fizziness, concentrate more CO2 in the headspace of the bottle. In practice, this might mean transferring contents to a smaller bottle, thereby making the headspace smaller.
Seltzer makers now run about $100, btw. I doubt whether they are economical, but they are probably entertaining. A 2009 Amazon review notes that obtaining CO2 canisters in the US can be expensive in practice.

2007 NYT Review:

I have set aside my Fizz Keeper.

Aww, I bought one of those to try and make carbonated water.

Seeing as FizzKeeper effectiveness has been debunked IMHO, I hereby declare Seltzer maker experiences to be on topic. Please indicate your country, as I understand availability of C02 canisters can vary.

I must admit I never thought of why CO2 and not other gasses are used. Should anyone care to experiment, I will volunteer to test soda pressurized with nitrous oxide.

I realise this was written a long time ago, but I’m very surprised this statement wasn’t challenged. The seal on a screw top bottle consists of the top being screwed on to the correct torque. Why would this not be repeatable by screwing the lid back on? (Obviously not possible with cans)

The gas has to be pumped back into the bottle with the seal in place. So you can’t re-pressurize the drink, and then put the original screw top back. The switch would depressurize it all over again.

Sure, but that’s about the contents of the bottle - Ficer67’s post appears to be saying something about the mechanical configuration of the closure.

Well, it was basically ignored. I can assure you that fizz keeper does keep some air in, though the seal of ordinary caps is apparently better. Once resealed, CO2 is added to the headspace from the soda until a new equilibrium is reached. It’s the opening and closing of the bottle that vents the CO2, if I understand it correctly.

Well, you could start with whipped cream from a canister…

This site helpfully lists the solubility of various gases in water. Argon, methane, hydrogen and Helium don’t appear to dissolve particularly well. The gases that do are typically poisonous or noxious: examples include chlorine gas, hydrogen sulfide, ammonia and sulfur dioxide.

The bottle’s in equilibrium before you open it, but once it’s open, it’s the partial pressure of CO2 that would determine how much CO2 comes out of solution into the space in the top of the bottle.

Adding more pressurized air wouldn’t change that partial pressure much at all, so the soda keeper wouldn’t work too well.

We had a fizz-keeper many years ago, but it didn’t help, and may have actually made things worse. In the thread linked to in the OP, Ike Witt wrote

I now think Ike Witt is mostly correct, but that his reason why may be wrong.

I bought a Jokari Soda Dispenser, which is screwed onto the pop bottle as soon as it’s opened. In the picture, you can see the flexible tube that dips into the pop. I cut that off. The pop got agitated flowing through that tube when it was being poured, making it lose its fizz in the glass when poured. Without the hose, I just tip the bottle before pushing the trigger. Pours much better, without foaming up in the glass. I also have to cut off the ring of left-behind bottle cap material on each bottle for it to make a good seal, which is a bit of a pain.

Anyway, I expected the bottle would inflate overnight each night, over the coarse of a whole bottle. It re-inflates once or twice, after pouring 10-12 ounce glasses, but after that, the bottle stays indented, so there’s basically just atmospheric pressure from then on. When I’m near the end, the bottle is very dented in in the middle, and I have to hold it upside down, and use my whole arm to squeeze the bottle to get any out.

I’ve gone on vacation for a week with a half to two-thirds full bottle, come back with the bottle still not fully inflated, but with some fizz still in the pop. More than I’d have if I just sealed the pop with the lid, or used the fizz-keeper.

For most of the bottle, there’s no pressure above atmospheric, so just squeezing the bottle to remove air should work just as well. I have never tried this, however.

I suspect that a big part of what helps it keep fizz in is that there isn’t any air in the bottle, and that Oxygen or Nitrogen dissolving into the pop makes the CO2 come out more readily. Writing this post, it just occurred to me it’s also possible that having the bottle squished reduces the interface area between the pop and headspace, and that this reduces the transfer of CO2 out of the pop. I’ll try adjusting how I squish the bottle to minimize the interface area.

Maybe I’m underthinking, but wouldn’t pressurized air above the surface of a liquid make it “harder” for the CO2 to escape and thus keeping more in solution? Kind of like raising the “boiling point?” Or am I just way off the mark?

Well, actually no. I’ve actually measured this at home in Michigan, and damn it, I don’t have all my notes. At home I make beer, soda-pop, and carbonated water, and for the last two, I use weight as an indicator of percent carbonation.

(Side note: the setup is dirt cheap, and virtually free to operate. Consider 20 pounds of CO[sub]2[/sub] [food grade spec’d, but even the welding stuff is already food grade] is only about $18, and lasts forever.)

So to “pull a vaccuum” on a half-empty soda-pop bottle, just squeeze it until the soda rises to the top. Cap it. Some of the CO2 will leave solution, and the bottle will fill, but it’s only a minute quantity of gas. Enough of the gas is still in solution so that it won’t go flat. Note: this is pretty much as opposite as one can get from the idea of a FizzSaver type of device.

With a FizzSaver, the added pressure doesn’t stop the CO2 from leaving solution. Rather you end up with atmospheric gas in the solution, and you don’t want that.

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.