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#1
08-11-2008, 06:37 AM
 Bravo Romeo Guest Join Date: Apr 2008 Location: Sydney, Australia Posts: 110
Does squeezing (and sealing) a soda/soft drink bottle keep it carbonated for longer?

My dad always told me it did as I was growing up and I just blindly believed until a few weeks ago. Now I'm plagued with doubt.

I did a quick search but couldn't find any Cecil studies on the subject.

Can anyone help me out, or link me to a Cecil report that I was too dumb to find?
#2
08-11-2008, 07:39 AM
 Khadaji Member Join Date: Mar 2002 Location: Southern Pennsylvania Posts: 21,599
I have found the opposite. By squeezing out the air, you make room for the carbonation.

If you wanted it to stay carbonated it would be better to pump air in. Here's a little gizmo to do that.
#3
08-11-2008, 09:12 AM
 robby Charter Member Join Date: Dec 2000 Location: Connecticut, USA Posts: 5,202

Carbonation in soda
#4
08-11-2008, 09:24 AM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
Quote:
 Originally Posted by robby We discussed this about a year ago in this thread: Carbonation in soda
Quote:
 Originally Posted by ticker I think what confuses here is the difference between the gas pressure, which would push the bottle out, and partial pressure which affects the rate of CO2 diffusion from gas to liquid. Partial pressure is related to concentration as well as the overall gas pressure so a relatively high concentration will give a relatively high partial pressure without necessarily requiring a high overall gas pressure. Therefore the partial pressure of CO2 may reach equilibrium levels without exerting much additional pressure on the sides of the bottle.
But, the way I understand it (read: going off memory, I can't be bothered to look it up ), total pressure is simply the sum of all partial pressures. In other words, the CO2 pressure is independent of the other pressures, and the additional air from the pumps serves only to maximize the volume of the container so additional CO2 is not needed to increase the container's volume?
#5
08-11-2008, 09:42 AM
 robby Charter Member Join Date: Dec 2000 Location: Connecticut, USA Posts: 5,202

Quote:
 Originally Posted by robby Former chemistry teacher here. Here's my hypothesis to explain what's going on. First of all, to a good approximation the other gases in the air space above the liquid in the closed bottle are irrelevant. Assuming the gases are ideal, gases don't interfere with each other. What's happening is that a characteristic partial pressure of gaseous CO2 builds up in the closed air space in the bottle. This pressure is dependent on the temperature of the liquid, and by Henry's Law, on the concentration of dissolved CO2 in solution. If the air space is small, only a relatively small amount of dissolved CO2 comes out of solution to build up the equilibrium partial pressure of gaseous CO2. If the air space is large, more CO2 comes out of solution to build up that characteristic partial pressure. If the bottle is left open, the air space is really large, and most of the CO2 comes out of solution until equilibrium is reached with the very small amount of CO2 present in the air around us, resulting in a flat drink. ...The key is that when you squeeze the bottle, you are decreasing the volume of the air space over the liquid.
This analysis assumes that the bottle will remain "scrunched up." If the flexible bottle re-expands to its original volume, the same amount of carbon dioxide will come out of solution as it would have if you had left the bottle closed up at its original volume.

Pressurizing the bottle with air depends on the fact that the gases are not, in fact, ideal, as well as the fact that some carbon dioxide is present in the pressurized air.

To maximize the carbonation of the drink, you would pressurize the air space with pure carbon dioxide.
#6
08-11-2008, 09:53 AM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
Quote:
 Originally Posted by robby To maximize the carbonation of the drink, you would pressurize the air space with pure carbon dioxide.
Just like we do when we expect a keg to last longer than an hour.
#7
08-11-2008, 10:00 AM
 si_blakely Guest Join Date: Jul 2002 Location: UK Posts: 4,935
My BIL recently claimed that compressing the bottle to reduce the head space created a pressure reduction in the head space as the bottle tried to expand - this would cause more CO2 to come out of solution to equilibrate the partial pressure. My theory is that a compressed PET bottle does not have enough elasticity to create a significant vacuum, and if you have a minimal remaining head space anyhow (maybe 1 cm at the top of the bottle) the amount of CO2 lost into that space (even under vacuum) will be less than the CO2 lost to the head space of a half empty non-compressed bottle.

Some simple experiments/math should give an answer pretty quickly.

Si
#8
08-11-2008, 10:46 AM
Quote:
 Originally Posted by si_blakely My BIL recently claimed that compressing the bottle to reduce the head space created a pressure reduction in the head space as the bottle tried to expand - this would cause more CO2 to come out of solution to equilibrate the partial pressure. My theory is that a compressed PET bottle does not have enough elasticity to create a significant vacuum, and if you have a minimal remaining head space anyhow (maybe 1 cm at the top of the bottle) the amount of CO2 lost into that space (even under vacuum) will be less than the CO2 lost to the head space of a half empty non-compressed bottle. Some simple experiments/math should give an answer pretty quickly. Si
I've never seen a "squished" soda bottle (under refrigeration; room temp/etc. is a diff. story) re-expand itself. I suspect squishing to reduce head space is the way to go.
#9
08-11-2008, 11:19 AM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
I've seen it at least 100 times. Obviously, YMMV.
#10
08-11-2008, 01:02 PM
 Khadaji Member Join Date: Mar 2002 Location: Southern Pennsylvania Posts: 21,599
Quote:
 Originally Posted by toadspittle I've never seen a "squished" soda bottle (under refrigeration; room temp/etc. is a diff. story) re-expand itself. I suspect squishing to reduce head space is the way to go.
I see it all the time. I like a little less carbonation, so I squeeze the bottle and let it sit.
#11
08-11-2008, 01:40 PM
 RedSwinglineOne Guest Join Date: Jan 2007 Location: Silicon valley Posts: 1,326
When I was a kid, my dad started squeezing our 2 liter soda bottles and I remember thinking it made the soda go flat much sooner.

I later found in one of his old science magazines (Omni I think), an article where they mentioned having had a contest where people wrote in with some kind of 'practical use of science in the home' idea. One of the winners was someone who suggested squeezing the extra air out of soda bottles. They later decided that that was a mistake, and not only did it not help keep the soda carbonated, but that it made it worse.

This seems like it would be easy to test, if you have a way to measure the carbonation.
#12
08-11-2008, 02:18 PM
 Tristan Guest Join Date: Sep 2000 Location: leaffan for president! Posts: 5,848
Sounds like this needs to be done.

For science!

If nobody has done it by then, I will purchase 2 bottles of soda on Friday.
#13
08-11-2008, 04:54 PM
 zut Charter Member Join Date: Apr 2000 Location: Detroit, MI Posts: 3,724
Quote:
 Originally Posted by robby This analysis assumes that the bottle will remain "scrunched up." If the flexible bottle re-expands to its original volume, the same amount of carbon dioxide will come out of solution as it would have if you had left the bottle closed up at its original volume.
I would think that whether or not the bottle re-expands would depend on what partial pressure of CO2 is required to maintain equilibrium. If it's over 1 atmosphere, the bottle will re-expand.

Following that trail of logic, that would mean that scrunching up bottles that are still highly carbonated won't help (and might hurt) because they would re-expand. Scrunching up lightly- carbonated bottles, though, might prevent the contents from going totally flat.
#14
08-11-2008, 06:50 PM
 si_blakely Guest Join Date: Jul 2002 Location: UK Posts: 4,935
Quote:
 Originally Posted by toadspittle I've never seen a "squished" soda bottle (under refrigeration; room temp/etc. is a diff. story) re-expand itself. I suspect squishing to reduce head space is the way to go.
In the interests of science, I squished a 2 litre PET soda bottle, inverted it, and stuck it mouth down in a sink of water.

The maximum height of water within the bottle was 10cm, but that took a very careful squeeze - compressing the middle of the bottle all round to avoid major creasing. The water level was much lower (5cm) with a flat "across the middle" crease.

So the internal pressure of a squeezed bottle is lower than atmospheric pressure, but not by much. If you have a squeeze and some head space (maybe 1/4 of a bottle), the partial pressure of the CO2 will drop and more will come out of solution.

A squeezed bottle with almost no head space will have much less impact on CO2 in solution.

Someone really needs to do some maths, comparing a 50% empty bottle with 50% head space, a 50% empty bottle squished with 25% head space, and a 50% empty bottle squished with 5% head space. It's too late for me here to do that sort of work, but we should have enough info to calculate it out.

Si
#15
08-11-2008, 08:29 PM
 Mangetout Member Join Date: May 2001 Location: England Posts: 57,812
One factor perhaps ignored in many of these discussions (although perhaps not very significant - I'm not sure) - when you pour your drink, you agitate the contents of the bottle, causing some CO2 to come out of solution - and this continues after the bottle is righted for capping. The gas in the headspace of the bottle is therefore probably not plain air - and may already contain quite a high proportion of CO2.
#16
08-11-2008, 08:38 PM
 DrDeth Charter Member Join Date: Mar 2001 Location: San Jose Posts: 37,738
This woudl be a good Mythbusters! Or maybe Cecil?
#17
08-11-2008, 09:39 PM
 Apocalypso Guest Join Date: Jan 2008 Posts: 1,816
Quote:
 Originally Posted by DrDeth This woudl be a good Mythbusters! Or maybe Cecil?
Mythbusters would do it with carbonated water instead of soda, adding juice to simulate the soda. They'd only do it twice, and conclude the myth was "busted".
#18
08-11-2008, 10:35 PM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
Quote:
 Originally Posted by Mangetout One factor perhaps ignored in many of these discussions (although perhaps not very significant - I'm not sure) - when you pour your drink, you agitate the contents of the bottle, causing some CO2 to come out of solution - and this continues after the bottle is righted for capping. The gas in the headspace of the bottle is therefore probably not plain air - and may already contain quite a high proportion of CO2.
It seems to me that there is much more gas being released that was already out of solution and sticking to the side of the container. Agitation increases the amount of nucleation sites; I guess it just depends on how rough you pour your soda.

Regardless, the equilibrium partial pressure is (mostly*) irrespective of the initial pressure or makeup of the headspace upon capping. It can even go the opposite way. For example, a flat keg can be purged with a high pressure of CO2 after it's been filled with air, and it will regain its fizzyness again. The taste will be suspect, but this is usually done with PBR, Coors or Bud Light, or another lovers-in-a-canoe beer, so the taste part isn't an issue.
#19
08-12-2008, 01:30 AM
 Bravo Romeo Guest Join Date: Apr 2008 Location: Sydney, Australia Posts: 110
Am I right in saying that a conclusion has not yet been reached?
#20
08-12-2008, 09:28 AM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
Quote:
 Originally Posted by Hyper Aware Am I right in saying that a conclusion has not yet been reached?
I think zut nailed it in #13.
#21
08-12-2008, 12:57 PM
 zut Charter Member Join Date: Apr 2000 Location: Detroit, MI Posts: 3,724
Quote:
 Originally Posted by si_blakely Someone really needs to do some maths, comparing a 50% empty bottle with 50% head space, a 50% empty bottle squished with 25% head space, and a 50% empty bottle squished with 5% head space. It's too late for me here to do that sort of work, but we should have enough info to calculate it out.
The results would have to depend on how much CO2 is in the beverage to begin with. This unofficial page says the initial volume of CO2 (at 1 atm) is about four times the liquid volume, and the pressure required to keep it in solution is about 2 atmospheres. I dunno how standard or accurate that is, but it seems like a reasonable place to start.

The amount of CO2 in solution is linearly proportional to partial pressure (I believe), so (for example) a drop in partial pressure from 2 atm to 1 atm would cut the "fizzyness" in half.

If you had a 50% empty bottle where the pop started with a nominal amount of CO2, the capped it, the system would regain equilibrium when 1/3 of the CO2 had left the pop, giving a partial pressure of 1-1/3 atm of CO2. If you had scrunched the bottle to minimize head space, it would be pressurized to 1-1/3 atm absolute. If you hadn't scrunched the bottle, it would be pressurized to 2-1/3 atm absolute. So no difference because of scrunching.

If you started with pop that was already half-flat (the initial volume of CO2 in the pop is about twice the liquid volume), and a bottle that was 50% empty, the two things could happen. If you DON'T scrunch the bottle, 1/3 of the CO2 would come out of solution, and the bottle would wind up pressurized to 1-2/3 atm absolute (one atm of air and 2/3 of CO2). If you DO scrunch the bottle, CO2 would leave solution and fill the head space UNTIL the system reaches equilibrium, with 1 atm (or a bit less) of CO2 partial pressure above the pop. That would mean *less* CO2 leaves the pop than in the non-scrunched case, and your delicious beverage is more fizzy than it otherwise would have been.

(I believe the above is approximately correct, but would welcome additions and corrections from chemists and beverage scientists.)
#22
08-12-2008, 01:12 PM
 unstrung Guest Join Date: Jul 2008 Location: Tampa, FL Posts: 359
Quote:
 Originally Posted by Apocalypso Mythbusters would do it with carbonated water instead of soda, adding juice to simulate the soda. They'd only do it twice, and conclude the myth was "busted".
Don't hate on the Mythbusters, I love those guys

In terms of the original question, what I'm getting from the folks who posted with very well reasoned explanations (and who also know much, much more than I do regarding the physics in play here) is that the real answer is "it depends on any number of things". Nobody has mentioned refrigerated vs. room temperature yet, but I'm willing to guess that plays a part as well. Thus, my prediction for this question is that ultimately, over time, the squishers will receive about the same fizzy benefit as the non-squishers.

And, as an aside...

My mom went through this phase where she would leave a bottle of cola in the fridge for days, without the top on. She did this specifically to get rid of as much carbonation as possible. Mom, you know I love you... but sometimes you are gross
#23
08-12-2008, 04:37 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 79,564
Quote:
 Pressurizing the bottle with air depends on the fact that the gases are not, in fact, ideal, as well as the fact that some carbon dioxide is present in the pressurized air.
Eh, it seems to me that how much of the gas is CO2 wouldn't really matter. Sure, you'll only get carbonization with carbon dioxide, but we don't really care about carbonization; we care about little bubbles in the drink. If some of those little bubbles are nitrogen and oxygen instead of CO2, what's the difference?
#24
08-12-2008, 04:45 PM
 Q.E.D. Charter Member Join Date: Jan 2003 Location: Richmond, VA Posts: 22,536
Quote:
 Originally Posted by Chronos If some of those little bubbles are nitrogen and oxygen instead of CO2, what's the difference?
Because carbonation isn't just about little bubbles in your beverage, it's about the distinct flavor imparted by the carbonic acid produced which results from dissolved CO2. You've never tasted flat soda? It's nasty on a level much different than the mere lack of bubbliness.
#25
08-12-2008, 04:49 PM
 Santo Rugger Guest Join Date: Nov 2006 Location: Obama Fe, NM Posts: 7,292
Quote:
 Originally Posted by Q.E.D. Because carbonation isn't just about little bubbles in your beverage, it's about the distinct flavor imparted by the carbonic acid produced which results from dissolved CO2. You've never tasted flat soda? It's nasty on a level much different than the mere lack of bubbliness.
Right. Also, ever played with dry ice in your mouth? It tastes a lot like carbonated water.
#26
08-12-2008, 04:52 PM
 Q.E.D. Charter Member Join Date: Jan 2003 Location: Richmond, VA Posts: 22,536
Quote:
 Originally Posted by Santo Rugger Also, ever played with dry ice in your mouth?
Is that wise?

I mean, I've handled the stuff, but I've never once considered popping a chunk in my mouth since I don't want my tongue to, y'know, shatter. Okay, I know that won't actually happen, but still...
#27
08-12-2008, 05:19 PM
 JSexton Guest Join Date: Jan 2000 Location: Snowy Oregon Posts: 4,758
Quote:
 Originally Posted by Apocalypso Mythbusters would do it with carbonated water instead of soda, adding juice to simulate the soda. They'd only do it twice, and conclude the myth was "busted".
And then find a way to make them explode.
#28
08-12-2008, 06:20 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 79,564
Huh, the only difference I've ever noticed between flat and non-flat pop is the mouth feel. Then again, on the occasions I've tasted unflavored carbonated water, I've found it quite disagreeable.
#29
08-12-2008, 06:52 PM
 Q.E.D. Charter Member Join Date: Jan 2003 Location: Richmond, VA Posts: 22,536
Quote:
 Originally Posted by JSexton And then find a way to make them explode.
You say that like it's a bad thing.
#30
08-13-2008, 08:33 PM
 CookingWithGas Charter Member Join Date: Mar 1999 Location: Tysons Corner, VA, USA Posts: 12,539
I found enough discussion on this to add it to my unofficial FAQ. Click to see a few other threads.

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