r/AskPhysics • u/motherbatherick • 3d ago
If you store a carbonated beverage upside down, will it maintain carbonation?
Hey everybody, I have a practical physics problem that I'm having trouble wrapping my head around.
I love gin and tonics, but I'm constantly running into the problem of my tonic water losing carbonation due to the fact that I buy it in either 1 or 2 liter plastic bottles (yes, I recycle them religiously. Even before you start. ;-) ). Convenient, except for the fact that no matter how much you tighten the cap, it goes flat quickly. So I had the idea of storing the bottle upside down in the fridge. My hypothesis is that even though CO2 doesn't rise, the reason why it releases when you open something carbonated is because of the super-saturation in the water, so storing it upside down *should* keep it from leaking out of the cap because it has a plastic barrier on top and a water barrier below.
Am I wrong here? I feel like I'm missing something. Like maybe the CO2 will release just as quickly from the water regardless of the bottle's positioning because the water is already super-saturated, so it isn't really an effective barrier.
Anyway, thanks for your help in advance.
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u/slower-is-faster 3d ago
No, this is why we have no soda in Australia
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u/charlie_marlow 2d ago
That's surprising. I saw a documentary about a young Albert Einstein splitting the Aaron to introduce bubbles to beer in Australia.
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u/NanotechNinja 3d ago
Swap to buying the small cans like Fevertree. You just use up a whole one making a drink, and aluminium recycles better anyway.
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u/motherbatherick 2d ago
Well, agreed about the advantages of aluminum, but another problem is that I'm a Type 2 diabetic, and Fevertree, while delicious, doesn't make a sugar free version. I have heard that Fred Meyer and Walmart make a sugar free version in cans, so I might try that.
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u/agate_ Geophysics 3d ago
Voice of experience: yes, keeping the bottle mouth under the liquid surface will keep the drink carbonated much longer. I don’t turn them upside-down, I just store them sideways in the fridge.
Folks who are thinking about partial pressure and Henry’s Law are on track except that the bottle cap never completely seals again once it’s been opened. It’s usually watertight, but it’s not gas-tight, so it slowly leaks out CO2 unless it’s immersed in liquid.
Speaking of partial pressure, I had a physical chemistry prof once who said he used to make fun of those air pump bottle caps that let you pump air in to re-pressurize the bottle: Henry’s Law says they can’t possibly work. Until he tried one, and it does work! He said probably the extra pressure tightens the bottle cap sealing surface, so there’s less leakage of CO2.
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u/HardlyAnyGravitas 3d ago
It’s usually watertight, but it’s not gas-tight
I don't think this is true. There is no reason why a cap can't be gas tight (enough). If they weren't the bottles would be flat before you bought them.
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u/Kiwifrooots 3d ago
Yeah I've had coke bottles well over 200psi before dropping pressure or popping.
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u/RbN420 3d ago
all the air you pump in the bottle is less carbon evaporating from the solution, even if the cap is supposed to leak
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u/agate_ Geophysics 3d ago
No, that was the physical chemist’s point: Henry’s Law is about partial pressure, all the different gases act independently, adding air doesn’t affect the dissolution of CO2 at all.
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u/Emergency-Drawer-535 3d ago edited 3d ago
Really? Air has close to zero % CO2. The soda has a higher partial pressure than zero. So wouldn’t it move from the soda to the air? Equilibrium will happen when the dissolved CO2 in the soda will exert a partial pressure equal to the partial pressure of the CO2 in the air. But I’m not a physicist
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u/agate_ Geophysics 3d ago
Yes, that’s right, and the same amount of CO2 will leave solution whether there’s low pressure air, high pressure air, or pure vacuum above the liquid. The behavior of the CO2 is independent of the other gases.
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u/Emergency-Drawer-535 3d ago
Ah right. If the air above the soda has enough pressure this will raise the partial pressure of ambient CO2. Since it is such a low amount, 4 parts per 10 thousand, it would take thousands of bars to drive the CO2 back into the soda. The container would explode.
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u/urethrapaprecut 3d ago
It's confusing but apparently this thread is saying partial pressure = concentration of just the CO2, it doesn't matter what other gasses are in there. I'd say I'm skeptical since like, they're all molecules hitting each other at a small emf scale, seems like the complete noninteraction of different gasses is likely an approximation, maybe a good one
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u/Dranamic 3d ago
Wait. Why don't they just sell carbonated beverages in bags, like cheap wine?
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u/devstopfix 3d ago
The bag will fill with CO2.
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u/Dranamic 1d ago
Wouldn't the partial pressure of CO2 at one atmosphere be considerably higher than normal air at soda bottle pressure?
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u/Temporary_Pie2733 2d ago
The bag is about keeping oxygen out, not keeping pressure up. I’ve never seen box sparkling wine.
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u/PM-MeYourSexySelf 2d ago
No. It's the pressure keeping the CO2 in the liquid, without pressure the CO2 slowly comes out of the fluid into the air. Conversely, adding more pressure forces the CO2 back into solution.
Generally that's impractical to achieve, since once you release the pressure CO2 will continue to come out of the solution until it stabilizes. That said, there is a small amount of leakage through the cap, so you'll continue to lose carbonation on an opened bottle. You might be able to preserve some carbonation by turning upside down so it creates a better seal, but every time you open it again it'll just lose a bit more gas that way.
So yeah, the only real way would be to store under pressure indefinitely. The drink can still go bad. I had some really old bottled soda once and it tasted real bad. But was still fizzy.
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u/Ahernia 2d ago
As you've discovered, loss of carbonation isn't a function of the tightness of the cap. Consequently, turning the bottle upside down isn't going to make any difference. The liquid goes flat because
- You've broken the seal and let out pressurized CO2, which is keeping the liquid carbonated
and
- The CO2 you let out was replaced by air.
When the bottle is opened and reclosed, the CO2 in the liquid will try to reestablish equilbrium with the air, which means some of the CO2 will leave the liquid and mix with the air until equilibrium is reached. Once you've opened the bottle, the only way to maintain the same carbonation is to repressurize the bottle with CO2.
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u/AppalachianHB30533 2d ago
Simple solution. Use up all the tonic water at once--mix a lot of gin and tonics! You'll definitely be happier! 😉
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u/DiabloConQueso 3d ago
Well, you have to turn it upright in order to open it (unless you want a giant mess), so the end-result is going to be the same no matter what orientation you store it in, since the CO2 is going to seep out of the liquid into the depressurized empty space of the bottle regardless of orientation.
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u/Useful_Expression382 3d ago
In a resealed bottle, carbon dioxide will stop falling out of solution when the partial pressure of the CO2 gas in the headspace reaches equilibrium with the concentration of the dissolved CO2 in the beverage. This is Henry's law. The orientation of the bottle doesn't make a difference and your problem exists because each time you dispense and reseal the bottle you have more headspace which means even more carbonation will be lost.
Store the drink in a smaller bottle or get a pump lid to pressurize the bottle before putting it back in your refrigerator.