Won’t make a difference. What matters is the partial pressure of CO2, and eliminating the dead space won’t affect that. It’ll inflate back up to the usual volume.
What would help is to move the soda to a smaller container. Say, a 1 L container after you’ve drunk half of the 2 L. But that’s pretty inconvenient.
That’s not quite the whole story. Colder water can hold more CO2 for a given partial pressure of CO2 in the ambient atmosphere. If there is very little headspace (as with a totally full bottle), then the temperature doesn’t matter–some gas will come out of solution, and the pressure of the headspace will increase, but there’s so little volume there that it doesn’t significantly change the amount of dissolved CO2. Only when you’ve consumed a significant amount does it matter, because there’s much more volume for the gas to occupy, and you’re wasting much more by requiring a high pressure for the same amount of CO2 in solution.
Quite true, of course, and this is why soda doesn’t need to be refrigerated in the grocery store. It’s also why I never buy big bottles of Coke – it eventually goes flat. I like the little individual serving 300 ml bottles, and if for some reason they’re not available, I’ll settle for cans. But the general principle remains that colder water can hold more CO2.
But I have effectively done that. Squeezing the bottle reduces its volume and once it’s capped tightly, it doesn’t inflate back up to its original size. Empirically, it does work.
Way back in ye olde days of the late 80s someone told me soda goes flat if it’s kept in the fridge. I scoffed. Later on I heard it again a couple of times. Still skeptical. Then I did some highly unscientific testing and failed to come to any conclusion. Eventually I did see some indications this was true and began to pay closer attention. Further experience indicated it might be true. Eventually, as a result of Al Gore inventing the internet it became possible to look for a resolution to this question online.
What I found was the repeated explanation that more CO2 will dissolve in a cold liquid than a hot one. This didn’t explain why I was finding that Pepsi went flat faster when kept refrigerated.
To be clear, this is not about an unopened bottle of Pepsi. It is what happens to the soda when a bottle is repeatedly opened, a glass of Pepsi poured out, and then the bottle is returned to the refrigerator. I found that online questions about why refrigerated soda goes flat faster are common, it is something experienced by others. And one day I found an explanation I didn’t really understand at the time, can’t find again, and can’t remember much detail about. In general, the idea was that more CO2 ended up in the air gap left in the bottle when it was refrigerated and each time the bottle is opened more CO2 escapes, so the soda will seem to go flat faster if refrigerated.
Pure confirmation bias on my part to take up this line of reasoning whether it was correct or not. But I’m still missing some detail on this matter so I’m going to stubbornly insist that it is true that soda goes flat faster in the refrigerator until I find an entire explanation that would explain my observations. One possible explanation I thought of long ago was that cold soda would ‘taste’ flatter than warm soda because it wouldn’t release CO2 as fast as warm soda when you drink it. I say ‘taste’ to mean the sensation felt in the mouth since I don’t you can actually taste CO2 or a difference in it’s content when drinking soda. But I still have questions.
I don’t think you’re talking out of your ass at all. You clearly know more about this than I do. As explained above I am just going to keep pushing until I get an explanation I can understand and confirm. I think that the amount of CO2 that leaves the soda and pressurizes the air gap must be limited by temperature and/or pressure. Just as you can cite Henry’s Law to explain that cold liquids can absorb more gas than warm ones there must be some similar explanation of the amount of CO2 that would end up in the air gap.
My understanding of gas laws is not even imperfect. It’s nearly non-existent except for the most basic generalities. I do think you for explaining that in reality the difference between CO2 solubility in soda is barely discernable because of the small Kelvin temperature difference. So it should hardly matter if soda is kept in the fridge or not based simply on the solubility of CO2 in a liquid. The answer may be that is doesn’t. @We_re_wolves_not_werewolves isn’t outright claiming that unrefrigerated soda goes flat faster than refrigerated, just that the opposite is not true.
I’d like to try some experimentation but I’m left with one problem in that regard, how do I tell how much CO2 remains dissolved in closed bottles of soda at any temperature? I can’t rely on the ‘taste’, as mentioned above cold soda might taste flatter because it doesn’t seem as bubbly. Anybody have any idea how to measure that without incredible sensitive scales or other impractical means for DIY testing?
I don’t have a way to test the actual CO2 percentage in a sample of Pepsi but I can test my perception of flatness in Pepsi kept at different temperatures. I have one 2 liter bottle in the fridge right now and another one out on the counter. I’m going to take an 8 oz. sample from each at approximately 8 hour intervals and taste them. By ‘taste’ I mean the sensation in my mouth from the carbonation. I’ll make a note if I can detect any noticeable change in pressurization based on the firmness of the bottle or the sound made when it is opened.
It’s not the same, because a squeezed bottle can’t have more than ambient pressure inside, and pressure is the only thing that can keep the dissolved gas from leaving the liquid. It’s basically the same as leaving it uncapped.
I don’t think that’s what he said. The difference in solubility is actually very significant–roughly a factor of 2 between a refrigerator and room temperature:
It’s very non-linear with temperature. But when talking about the pressure in the headspace, the ideal gas law holds, which is roughly linear. To halve the pressure, you’d have to halve the temperature in kelvin. But a 25 K difference is less than 10% of the absolute temperature.
According to the chart on this page, a liter of water at 36F (2C) can hold about 3.2 grams of CO2, while a liter at room temperature 72F (22C) holds about 1.6 grams, so half as much.
Actually… on thinking more, I’m less sure of this. What I said was true for overall pressure. But what matters here is partial pressure. And squeezing first means–once the bottle inflates a little bit–a partial CO2 pressure of 1 atm. It’s not as good as a partial pressure of ~3 atm with a new bottle, but it’s way better than the partial pressure of 0 atm with an open bottle or one that you left with lots of headspace.
I think the issue here is one of equilibrium. The equilibrium level will be the same whether you squeezed it or not since the empty space in the bottle is the same once it inflates. And it starts with the same negligible CO2 level, so the same amount has to leave to solution to end up with the same equilibrium partial pressure. But while that’s happening, squeezing does give you a 1 atm starting point, which probably slows things down a bit. If you expect to drink the rest in a day or two, it might make a meaningful difference.
Of course it doesn’t have more than the ambient pressure, but it has much less air. That means at any given partial pressure of CO2, there is less CO2 in the air. If the bottle is uncapped then the air that was in the bottle will mix with the atmosphere and the partial pressure will never be more than it is in the atmosphere.
My apologies to @ASL_v2.0 for misinterpreting his post.
Not necessarily true. CO2 is a heavy gas and may well sit in a layer above the soda even when uncapped. It’ll be strongly dependent on airflow, etc. in the fridge, though.
Probably not, depending on how long you leave it:
We’re presumably just talking a couple of days. And there isn’t much airflow in a typical fridge; plus the small opening will tend to reduce the mixing. CO2 can absolutely be retained in a large pit; people die semi-frequently from that. I don’t have any direct intuition about the CO2 in a bottle but it wouldn’t surprise me if it could stay stratified for a while.
I think opening the bottle and pouring out some of the contents will remove nearly all the accumulated CO2 whether stratified or not. Maybe different if you only removed the cap for a while and let it sit undisturbed.
Well it’s obviously time for an experiment. Two 2 liter bottles of the same soda. Each with one glass removed. One left uncapped in the fridge, one squeezed and recapped in the fridge. Then wait … hmm how long I can only really test well once … and I’m not sure what method to use for testing other than a blindfold taste test.
Any thoughts?
Sure, but then some amount will be emitted again. Once a small amount builds up then the layer just above the liquid will have a partial CO2 pressure of close to 1 atm–just as in the case of the squeezed bottle.
Sorry, misunderstood. I thought you meant about CO2 stratifying in a sealed bottle. If the cap is off, then CO2 will continue coming out of solution until it pushes all of the air out and establishes a nearly pure CO2 environment in the bottle - and then it will continue coming out of solution until the soda is flat.
Eventually. But OldGuy’s claim was that in a squeezed bottle, it doesn’t fully reinflate. So it must not be emitting enough gas to fill the remaining dead space. If so, then it wouldn’t fully displace the air in an open container, either. If–that is–the rate of CO2 emission was the same. Which it should be if the temperature and partial pressure of CO2 was the same. If CO2 stays stratified, then you’d have a partial pressure of 1 atm in the open case, just like the squeezed case.
I don’t suppose you have an accurate scale? We’re talking differences on the order of a gram total, so you’d probably want about 0.1 g resolution to really see a difference.
You’d also have to account for evaporation, but you could have a control for that.
A pH test might be possible as well, but I’m not sure about how that would manifest.
Or you could transfer it to a smaller container, put a balloon over the top, and then heat it moderately to drive out the remaining CO2.