# Retaining soda carbonation

I have a friendly dispute: does squeezing the sides of a half empty plastic soda bottle help to retain the remaining carbonation (by leaving less air space above the remaining soda), or does this increase the rate at which the carbonation leaves (i.e. the soda goes flat actually faster) - or is there no difference at all???

thanx, Robert

I’m pretty sure the only way to keep the carbonation from coming out of solution is to pressurize the can. If you plug up the drink hole with an airtight seal, then I guess squeezing the can might help. But otherwise, squeezing the can wont speed up or slow down the flattening process. But, I’m just a dumb college student, I could have this all wrong, but I doubt it.

It seems to me that carbonation will leave the soda until it reaches some sort of equilibrium. It leaves, basically, until the pressure inside the soda bottle is high enough that CO[sub]2[/sub] is reentering solution as fast as it leaves. That amount of pressure is going to be significantly higher than atmospheric pressure, which means that by the time the bottle reaches equilibrium - i.e. has a high enough pressure, it’ll probably have reinflated the bottle anyhow. Seems to me, then, that you’re wasting CO[sub]2[/sub] reinflating the bottle.

Just my guess, though.

This question resulted in a rather toxic thread a couple of years ago. Here it is.

Squeezing the bottle will do you absolutely NO good in keeping the bubbles in the pop. If it has any effect it all, it’s a negative effect: if the pressure inside the bottle is negative, due to the flexible bottle “trying” to regain its shape, that lessened pressure will cause more bubbles to escape. Only positive pressure will keep the bubbles in solution.

This is why pop in plastic bottles goes flat faster than that in glass bottles. Plastic bottles stretch, so if you agitate a plastic bottle half full of pop, the bubbles will escape. AT the point where a glass bottle’s rigidity does not allow the volume to expand any further, and the pressure equalizes, the plastic bottle will continue to stretch a little, thereby allowing more room for escaping gases. The glass bottle keeps the gas in solution because it doesn’t provide that extra escape volume. So when you open the bottle, there’s less gas to escape in a glass bottle, because it’s still in solution. Plastic bottle, the flex allows more escaped gas, which then escapes the bottle upon opening. Et viola, more escapes than with glass, so it goes flat sooner.

The misconception in the previous thread is that the OP was asking one question and finding, on his own, answers to another. The conditions he was talking about have to do with getting the CO[sub]2[/sub] into the liquid in the first place; the question he asked was about how to keep it there. Overall pressure, not CO[sub]2[/sub] concentration, is what counts in keeping the CO[sub]2[/sub] in solution. Mr. Yax, sqeezing the bottle is more likely to reduce the pressure, so I think you’ll find that if you refrain from doing so your fizz might last even longer. It’s not the exposed surface area, in this instance (although the surface area is not irrelevant), but the pressure that’s important.

I am assuming that you can apply an airtight seal, so that the plastic bottle retains its “squeezed” shape.

That doesn’t make any sense. The bottle is airtight if you put the cap on hard, but gas is released by the soda - that’s what causes the fizzy feeling in your mouth, and that’s why it goes flat. Once all the gas is released, the fizz is gone. Since gas is being released inside the sealed bottle, how could it retain its squeezed shape?

The bottle won’t retain its ‘squeezed’ state even if it has an airtight seal. CO[sub]2[/sub] in the headspace above the soda must eventually come into equilibrium with the carbonic acid and CO[sub]2[/sub] in the liquid. That usually happens at greater than normal atmospheric pressure, so a sealed, flexible bottle will inflate.
More details in this thread: Pressing Scientific Issue: Do Pump-Caps Preserve Soda Fizz?, Part II

Exactly. That’s why squeezing the air out of a bottle is more like to accelerate the flattening process, rather than retard it. By squeezing the bottle you’re just making more room for the gas to come out of the soda. If you put an open bottle of soda in a vacuum, the CO2 will boil right out of it, immediately. A squeezed bottle is not a true vacuum, but the reduced pressure will still “draw” more CO2 out of the soda than a pressurized bottle.

The OP of that thread is not very careful about distinguising between “restore” and “preserve,” which is the crux of this discussion. Pressurizing a bottle with atmospheric air will help PRESERVE whatever CO2 is already in solution, but it will not RESTORE any lost CO2. Pressurizing with pure CO2 WILL restore lost CO2.

My understanding is that the OP of THIS thread is about PRESERVING the fizz, not restoring it. In which case, no, squeezing the bottle does NOT help preserve the fizz. It’s POSITIVE pressure that helps preserve it, not NEGATIVE pressure. You’re more likely to get negative pressure by squeezing the bottle before you close it.

And YES, the pump top thingies in the other thread DO help preserve the fizz, though they will not restore lost fizz.

Yeah, um, that’s what I said in my first post.

Wow, a thread where people have to keep repeating things in order for them to sink in? At the Dope? Huh.

IOW, Ex, I’m agreeing with you.

Store the plastic bottle upside down. The fizz has no where to go!

The challenge of getting a 2 liter bottle to stay upright in the fridge when placed wrong side up is an exercise left to the reader.

Actually, you’re probly fooling yourself. The fizz doesn’t fade because it leaks, it fades because the elasticity of the plastic bottle is not as good at keeping it in solution. That doesn’t change with the bottles orientation.

If you have a bottle that leaks air, it’ll probably make a mess if you turn it upside down. If you do so and it DOESN’T leak, you probly don’t have an air leak in the first place.

I buy soda in 2 liter plastic bottles and I’ve had the habit of squeezing them for years.
I truly don’t know if it helps maintain the carbonation or not, but I can tell you that the
bottles do not inflate themselves, they stay squeezed.

If they’re not agitated, or heated, then no, they probably wouldn’t inflate. But you’re not actually accomplishing anything by squeezing. Even if the difference is infinitesimal, which is certainly possible, it will be on the side of flattening rather than preserving.

PLastic bottles loose their fizz quicker than glass over time because the PET is permeable to CO2. The gas leaks out through the plastic.

• Squeezing the sided of a plastic bottle won’t help at all in maintaining any fizz. Once you crack the cap, CO2 evaporates out until the bottle reaches sufficient pressure to stop that (assuming you re-capped the bottle) or until there’s no more CO2 to escape (which is why your squeezed bottles never expand back to full shape–there’s not enough CO2 in them to allow that).
• There are air-pump caps you can get that attempt to “re-pressurize” the bottle after it’s opened, but the problem with these is that they re-pressurize not with CO2 but with air–which could (over a period of a few hours I suppose) have an effect on the taste of a product. By far the best way to dispense soda is from a soda siphon, also called a “seltzer bottle” (tho technically seltzer bottles contain only mineral water and CO2) and often misspelt “soda syphon” (?). You pressurize these with special 8-gram CO2 cartridges (not the 12-gram ones for airguns, food-grade ones are 8-grams. 12-gram ones have oil in them, and are too big to fit intentionally).
~