Ways to keep Carbonated drinks from going "flat"??

[Mad Scientist]

In supermarkets you can buy this device that has a one way air sytem. Basically you hust screw it on to the top of your bottle and before you take a drink you give it a couple of squeezes and this is supposed to re-fizz the drink. Wither it works or not i am intirely sure.

[mulreay]

This has to be the most ridiculous topic I have ever read. We know as FACT you CANNOT keep CO2 in a 'fizzy' drink as the pressure of the drink is more than the ambient pressure of the room. You CAN'T contain a higher pressure within a lower pressure unless you keep the lid on. I have a design for perpetual motion if you would like to see it :sigh:

[Cap'n Refsmmat]

If you had read, you would see that most here are discussing keeping carbonated drinks stored in bottles.

 

Please read before you choose to insult.

[mulreay]

If you had read, you would see that most here are discussing keeping carbonated drinks stored in bottles.

 

Please read before you choose to insult.

 

Is that a joke?? sorry I don't get it.

 

As you will see my post is completely within the realm of this topic. Are we discussing, CO2 outside a water based beverage or are we looking at something I missed?

[Cap'n Refsmmat]

You said it's stupid because you can't keep CO2 in without a lid. Everyone's talking about keeping CO2 in a beverage while they're stored with a lid.

 

After an initial use, perhaps, but with a lid nevertheless.

[DrP]

This is the tip I was waiting to see come up. It's never sounded right, because you are reducing the pressure in the bottle, and it's nagged at me.

 

 

 

 

I agree - by squeezing the air out of the bottle that air is then replaced by gas that was dissolved - it will therefore make the drink loose more gas rather than keep it. Loads of people believe this will work, but logically it doesn't make sense all. By keeping the air in the bottle and putting the lid on tight surely less gas can escape because there is less room for it to escape. (I can see this where people get confused - they sqeeze out the air and think there is no room for the gas to escape because the liquid fill the bottle - - but off course the bottle isn't full (just squashed) and WILL fill from somewhere, which will be from the gas that comes out of the solution, making the drink flatter). This business about shaking the bottle to build the pressure must also be rubbish - by shaking it and building the pressure you are removing the dissolved gas again by fizzing it up - much better to use the air that is already in the bottle surely.

 

We had this discussion in the labs a few years ago - I was amazed that the majority seemeed to think that this would work. If you think about it logically - it doesn't. If I have missed something then please point it out to me because it seems so obvious to me.

[tomgwyther]

Having C02 as the primary gas in the half empty bottle does keep the beverage more fizzy. (As in a beer keg) But you have a point in that the Co2 in the bottle must come from the beverage itself in this case. I would always advocate the squeezy bottle approach

(Also, Adam hart Davis advocated this approach in a presentation about gas and pressure.)

"If in doubt, try it out"

I'm off to the shops to get some 1/2 litre bottles of coke.

I shall be posting the results shortly.

[Mr Skeptic]

For dissolved things, isn't partial pressure more important than total pressure? Therefore, squeezing the bottle to remove the air, so long as it remains squeezed, would lower the volume that CO2 has to expand to at equilibrium. But then if your bottle expands again to its original size, this would be moot. I've never tried that, but it seems to me that the bottle would regain its original shape.

[emcelhannon]

I seem to remember an explaination on why menthos cause such a reaction. Apperiantly it's not a chemical reaction in the normal sense. It's just that the menthos is so porous, it has a lot of surface area, a whole lot of surface area.

That's a part I don't understand. Apparently there's more than just pressure keeping the Co2trapped in the drink. Otherwise, it would all release when opened. Like seeding a molten metal to trigger it's crystal formation, something else aids in the release of the Co2. A bottle that hasn't been shaken may not releas any Co2 at all.

 

I'm just sayin, It's more than a atmosphereic pressure thing. I'm hoping for an expert to tell me what.

[Mr Skeptic]

It's also a surface area, and surface tension thing. Surface tension is very, very strong on small bubbles. A nucleation site helps reduce this. Once a small bubble is formed, it is much easier to expand it. Bubbles increase the surface area over which the liquid can dump CO2. Shaking is particularly effective as the nucleation sites are themselves bubbles so have even less initial surface tension to contend with.

[DrP]

For dissolved things, isn't partial pressure more important than total pressure? Therefore, squeezing the bottle to remove the air, so long as it remains squeezed, would lower the volume that CO2 has to expand to at equilibrium. But then if your bottle expands again to its original size, this would be moot. I've never tried that, but it seems to me that the bottle would regain its original shape.

 

In my experience the bottles always end up back in their origional shape - the volume of which would be filled by the dissolved gasses coming out of solution. Whether or not this is better than just keeping the lid on tightly in the first place I don't really know - It would seem like a good bet to assume that this would actually be worse as the volume is being filled by the dissolved gasses that you are actually trying to keep in solution.

[emcelhannon]

Surface tension is very, very strong on small bubbles. A nucleation site helps reduce this.

 

 

 

Thanks a lot. That explains a lot. I think I'll try squeezing the bottle with a clamp. That will expel the air, reduce the surface tension, and maintain atmosphereic pressure.

 

My next question for Mr Skeptic is why do small bubbles have greater surface tension? I don't see why less surface area would have anything to do with it. Is the Co2 actually in liquid form or microscopic bubbles? What exactly is the nature of the trapped Co2?

 

Thanks

[wargolem]

The question that is haunting me about all this is the assumption of a negative pressure inside the bottle. How is it that when you screw the cap back on the 2 liter bottle partially filled with soda (coke), that you are sealing in a vacuum? (negative pressure is a vacuum is it not?)

 

It seems that everyone who is saying that you have a negative pressure is saying that something that is capped at atmosperic pressure suddenly becomes a negative pressure and i am wanting someone to back that up.

 

I understand the people who are saying that "over time" the bottle will pop back to its original shape, that would make sense, but it is because of the gas escaping solution to find equalibrium with the gas above it that causes this, and therefore this implies that you are adding gas to a finite system which will INCREASE pressure which in turn will exert a force on the inner wall of the 2L bottle pushing it out to its original form.

 

I may be wrong here but if there is a negative pressure inside a closed system, then it would want to cause the 2L bottle to further collapse instead of expand would it not?

[JohnB]

I use the squeeze technique and it does work, after a fashion. The soda still goes flat, but takes longer to do so.

 

As it was explained to me years ago, the CO2 will come out of the fluid until the equilibrium is reached. By sqeezing the bottle there is a smaller volume of air that has to reach equilibrium and therefore less gas comes out of the fluid.

 

Less CO2 is required when there is only 10 ml of air than if there is 200 ml of air, so less gas is lost from the fluid.

 

I have no idea if it's right, that's how it was explained.