Cola behaves differently in various bottle sizes ???

[SteveBzzz]

Greetings,

I am puzzled by the seemingly different behavior that Cola exhibits under different bottle sizes. For example, I opened a new 2 liter bottle of Coke. I then distributed it between 2 smaller containers and the remaining in the Original Bottle.

The Coke distribution is as follows:

Bottle 1: Filled to Capacity , 0.5L (Approx).
Bottle 2: Filled to Capacity , 0.5L (Approx).
Bottle 3: (Original) Contains , 1.0L (The Remaining).

After 2 hours, all of the bottles are opened, and their contents are tasted. The results that I experienced are as follows:

Both bottles 1 and 2 were "flat" (Less carbonation), and had a displeasing taste. The Coke in bottle 1 maintained the same taste and carbonation level that it originally had (Approx.)

My question is this: Why does the coke in the smaller bottles lose carbonation, while the coke in the larger bottle remains unchanged? Here are some of my observations.

After a small amount of time (1 hour), the smaller bottles are highly pressurized and the containers are generally hard to squeeze. The larger bottle is easy to squeeze. Why does it seem like the smaller bottle is under more pressure than the larger bottle, but yet the soda from the larger bottle is more carbonated and tastier? All containers were filled with extreme caution so as not to produce surface "fizz." The containers were both cold from refrigeration.

Also, I recently purchased one of those pumps that replaces the bottle cap of a soda container. When pumped it re-pressurizes the container, supposedly maintaining freshness. The instructions say do not pump to such a degree that you cannot squeeze the bottle, as this device is more effective at a lower pressure. Why not higher?

What am I missing?

Any help would be greatly appreciated.

Thanks

 

[azg]

Milk with rootbeer? Yummy...

 

[IFRs]

My 2 cents:

Repeat your initial experiment but prior to capping all the bottles, taste from each. Maybe the flatness happened right away.

 

[donmackenzie]

I think I have two answers for you...
First, with respect to you chocolate milk life question: A lot of chocolate milk is UHT pasteurized and can therefore be stored for long periods of time without going bad. In Europe and Australia (among others perhaps, I have no idea) it's quite common to buy UHT pasteurized regular milk that you can then keep on the shelf for months, without refrigeration. However, UHT milk tastes wretched, which probably explains why those of us in North America, with our more discriminating tastes, can only tolerate the stuff if it has chocolate flavouring in it.

As for a pump to pressurize and thus preserve your cola... I don't think this would work unless you were to pump the headspace full of CO2. The equilibrium between dissolved and gaseous CO2 depends only on the partial pressure of CO2 in the gas phase. Ambient air contains too little CO2 to make this practical. You can buy small (12 g I believe) cylinders of CO2 for applications like bicycle tire inflators and air gun propellants. Best of luck.

Thanks very much, now I have to try this coke experiment myself to try and figure it out.

 

[IFRs]

donmackenzie -
My wife's family was in the seltzer business back in the roaring 20's and 30's. For a long time, we had a little pump they gave us that we used to re-pressurize Coke bottles after openning. It sure seemed to keep the soda tasting fresh for much longer than without it.

 

[TomSD]

Can't help it! Have to add my two cents, pedantically.
Hint: How do we spell "SUPERSATURATION"? How about "NUCLEATION SITES"?

No matter how the CO2 is added to a soft drink, it is obvious that there is more CO2 in a soft drink than would be in equilibrium with the small content of CO2 in atmospheric air since a soft drink container is pressurized, at least slightly, when you buy it. The vapor space of the container has a fairly high content of CO2; still not enough to cause any harm.

The amount of total "CO2" dissolved into the liquid is primarily determined by the following equilibriums:

1) Physical dissolution of CO2 gas
CO2(g) <--> CO2(aq) math: [CO2(aq)] = Kg PCO2
i.e. the concentration, [] indicating mole per liter of CO2 dissolved into the liquid where it is part of the aqueous (water) solution ( thus CO2(aq) ) is related to the partial pressure of the CO2 gas, PCO2, and the constant relating these quantities, Kg, (or 1/Kg', depending upon definition) is Henry's Law constant which varies with temperature, somewhat with concentration of other components of the solution, and slightly with pressure (usually neglect pressure variation, particularly up to about 5 atmospheres pure CO2). At total pressures generated by small pumps, forget about the total pressure making a difference in this equilibrium. The total pressure is sum of the partial pressures of the gas components so adding air (~79% nitrogen and ~21% oxygen and only about 0.03% CO2) pressurizes the container by increasing the partial pressures of nitrogen and oxygen. Okay, there is a small increase of CO2 partial pressure but it is very small. Okay, also there is some increase of dissolved nitrogen and dissolved oxygen due to the increased pressure (same equilibrium principles but smaller constants); the dissolved N2 and O2 will pop out when the pressure is released but it is small compared to CO2. There is a another reason for increased pressure (with an air pump) to help maintain &quot;freshness&quot; (carbonation), see below, but it is the CO2 partial pressure which governs in the dissolved gas equilibrium not the total pressure (to any appreciable extent). However, CO2 also interacts chemically with water, which nitrogen and oxygen do not. Hence, more equilibriums...

2) Hydrolysis
CO2(aq) + H2O <--> H2CO3
math: [H2CO3] = Kh [CO2(aq)]
Carbonic acid ( H2CO3 ) is formed which is actually not that weak as acids go meaning it dissociates fairly easily. Hence ...

3) Dissociation
H2CO3 <--> HCO3- + H+
or H2CO3 + H2O <--> HCO3- + H3O+
math: [HCO3-][H+] = Ka [H2CO3]

These latter equilibriums increase the total amount of CO2 that is absorbed into a water solution. With the right data for these equations, one can calculate the total amount of CO2 dissolved in the solution but ONLY WHEN EQUILIBRIUM is reached which can take a long time. This might be done for the original carbonation process (e.g. supposing the liquid is highly pressurized in a stirred vessel with a pure CO2 gas before bottling) and calculations would give the residual amount of CO2 in a soft drink that has gone totally flat and is in equilibrium with atmospheric air pressure.

When a soft drink is opened, the partial pressure of CO2 above the liquid is reduced but it doesn't explode. Yes, shaking before opening will cause a lot of initial &quot;foaming&quot; and you can feel a greater pressure on the wall of a plastic container that has been shaken but this is the result of the liquid already being supersaturated with CO2 and carbon dioxide seems to supersaturate water solution quite easily. Other gases can also supersaturate but not as much as CO2; don't forget about those other equilibriums which also take up CO2 into the solution.

Supersaturation means that the actual concentration of the CO2 in the solution is higher than the equilibrium concentration and it is a meta-stable condition like an egg balanced on a sharp point. A shock like a sudden temperature change (contact with ice), or a shake will induce a change towards the more stable condition; CO2 gas will come out of the liquid.

In a closed bottle, shaking causes some gas to come out and the partial pressure of CO2 increases so the total pressure increases as well; it doesn't take much CO2 release to raise the partial pressure enough in a small space to attain a condition near equilibrium. If the bottle is opened at this point, the agitated contents will spew forth since the shock is not yet dissipated, but if the bottle is left standing for a long while, things settle down, the higher pressure dissipates through the cap seal (and somewhat by permeation through the plastic) and the solution becomes supersaturated again as the pressure falls, there is not a lot of CO2 lost but the drink will become flat a bit sooner than if the bottle was not shaken.

Even without any shocks, the CO2 will continue to be lost as the supersaturated condition still slowly works toward equilibrium. As noted in the other replies, this is faster in a plastic bottle than in a glass bottle due to permeation loss. Smaller plastic containers do have more permeation loss due to a larger specific area (area per volume). In a more impermeable glass bottle, the loss is more likely around the cap seals which aren't perfect.

When a container is opened, air mixes with the gas in the vapor space of the container, CO2 content/partial pressure decreases and there is a greater driving force for CO2 to come out of solution. Yet, leaving the container alone, it will still take quite some time for equilibrium to be reached and the soft drink to be fully flat. First the dissolved CO2 near the surface comes out, as the concentration of dissolved CO2 decreases, the other chemical equilibriums shift towards dissolved CO2, more dissolved CO2 can come out of solution. As the concentrations near the surface are depleted, more of the CO2 components from lower depths diffuse upwards, etc. So it takes awhile.

Pouring the liquid into another container, even very slowly, will set up slow currents that help to keep the concentration even throughout the whole volume and the CO2 will come out faster. Especially in the container receiving the liquid while the remaining liquid in the original container still seems to retain its carbonation longer even though it probably has similar currents set up due to the pouring action (okay, probably somewhat to a lesser extent). However, the major factor for the faster rate of CO2 loss in the receiving container is due to the exposure of the carbonated liquid to a new set of nucleation sites.

The CO2 gas coming out of solution has to form a bubble which is not that easy by itself. A nucleation site makes it easier for the bubble to form; so more nucleation sites, more bubbles. Once a tiny bubble forms, it is easier for more CO2 to join this bubble. It is easier for more CO2 to join a bigger bubble than a smaller bubble.

The original container has nucleation sites but these have been &quot;conditioned&quot; by prolonged exposure to the carbonated solution. Nucleation sites in a different container also hold on to a bit of atmospheric air when the soft drink is poured in (aside from residual dust or other extraneous material providing additional sites) so these nucleation sites are more active. Also, smaller receiving containers have more sites per volume than larger containers. So there is more fizz in the smaller receiving containers and they go flat faster. The fizz, or rising bubbles, also stir the contents a bit. If we pour into a container with ice, there is thermal shock, more convection currents, greater exposure of liquid to air, and (believe it or not) more nucleation sites (quality of the ice water is probably a factor as well, hmmmm? i.e. more contaminants, more imperfections = more nucleation sites); most of these factors have been raised already.

If we can make the bubbles smaller, then the rate at which CO2 comes out of solution will be slower. Gas volume is inversely related to pressure. So pumping up the orginal container with air (even though it is not CO2), can slow down the loss of dissolved CO2.

That's how I see it.
Although this is a bit of fun, there are serious industrial and medical applications/problems related this subject.
Regards

 

[azg]

Tom, WoW! That was a cool dissertation there. Your spelling of &quot;SUPERSATURATION&quot; and &quot;NUCLEATION SITES&quot; was immaculate Would you mind addressing the issue of pouring cola onto ice cubes (variation of amount of fizz with the size / shape of ice and other materials) and mixing milk with root beer? These issues were touched upon here, but never to the depth. I predicted that smaller ice cubes should create more fizz. What do you think?

Cheers!

 

[TomSD]

Sorry about any rambling or hasty generalizations, azg.
You seem to have covered the important factors of fizzing on ice, i.e. increased area which not only increase air-liquid contact but also allows for more nucleation sites. So according to the logic, there should be more fizzing if the ice pieces are smaller since the smaller pieces have more area per volume.

You mentioned other factors such as a thin water layer on the ice which could &quot;smooth&quot; the surface and reduce nucleation sites. I think that you will get more fizzing if the soft drink is poured over &quot;fresh&quot; ice (straight from the freezer).
I am also pretty sure (haven't had any time recently for field shtudies) that you get more fizzing on ice if the soft drink is warm (not stored in the fridge) for two reasons:
1) greater thermal shock disturbs the supersaturation condition more, and
2) gas solubility is generally lower at warmer temperatures so the CO2 will tend to come out of solution faster.

I would tend to disagree with the thought that the water layer on ice promotes fizzing through carbonic acid formation/decomposition. However, this leads into the specifics of how the equilibrium constants differ in various solutions.

Generally, gas solubilities decrease in aqueous solution when the concentration of other added components increase so diluting the soft drink with water should increase the solubility and reduce the amount of CO2 escape (but the amount of water on the ice is small and won't change the overall concentrations very much during the pouring).

Gas solubilities are often compared simply on a basis of &quot;values&quot; taken to be the Henry's law constant but are really the total amount of gas absorbed at particular conditions. Such a comparison mistakenly ignores the other chemical interaction equilibriums that might occur.

Any acid gas such as CO2, chlorine, sulfur dioxide, etc. will have chemical interactions with water. Also, there can be other chemical equilibriums involved. For example, the water hydrolysis of chlorine forms two acids, hydrochloric acid (HCl) which essentially dissociates completely in to hydrogen ions (H+) and chloride ions (Cl-) and hypochlorous acid (HOCl) which is a weaker acid for which the dissociation equilibrium must be accounted for in calculations; and more interestingly, chlorine also complexes with chloride ion to form a trichloride ion:
Cl2(aq) + Cl- <--> Cl3-.
One can talk about other complexations of components and hydrations, etc. which are usually ignored under typical conditions and lower concentrations of the components.

It is possible that there are interactions of CO2 with other components of the soft drink solution. I haven't studied it, but have suspicions that there might be interactions with sugar. If so and if they are significant, then a case might be made for a thin water layer on ice causing more fizzing.
One can also bring surfactants into the issue. A component of the soft drink may suppress bubble formation and contact with water could reduce the surface concentration of the component enough to remove the suppression of bubble formation, if so, more fizzing.
These are only speculations on my part. I think there is greater fizzing on fresh ice compared to ice having a water layer but would have to re-do observations.

Mixing milk with root beer...
Regurgitation rather than speculation comes to mind.
Definitely a more complicated mixture.
Milk contains &quot;fats&quot; and compounds that could be surface active.
Never did it. I'll try to think about it.
Regards

 

[azg]

LOL, Tom! I wouldn't even think about it (milk + root beer). I once mixed hot milk and vodka (I was then a young and stupid ChemE student, and it was on a dare) inside of me. Yuck!

Seriously, I think milk and root beer would cause a different kind of foam: extremely dense, with very low content of gas. Which may cause the CO2 (g) to have a different dynamics than cola on ice: at first there will be rapid foam formation, and then it will achieve an equilibrium at a different concentration, as CO2 will reach saturation in the foam and the partial pressures will equilibrate.

 

[TomSD]

I think you're right, azg. Milk is mainly an emulsion where most of the &quot;fat&quot; components aren't actually dissolved but stay dispersed for a long time throughout the solution because they are so finely divided, especially after homogenization. The tiny particles of fat would provide nucleation sites for gas evolution, especially with the added thermal shock due to contact with ice. So an initial fast rate of foaming. A dense foam would imply the presence of surface active components that stabilize the gas bubbles. I seem to recall this being the case in ice cream soda float drinks. The dilution effect of more solution would help in reaching the equilibrium condition faster but the drink is then pretty flat.

Hot milk and vodka!
I'm going to the restroom now.
Regards

 

[azg]

Hey Tom,

Actually this has been bothering me ever since, but I decided never to proceed with experimentations in that direction anymore: what happens to the hot milk and vodka in an acidic environment at 37 degrees C? What exactly was it that decided to shoot up?

 

[TomSD]

Gag reflex, depending upon your constitution?
Biochemistry is not my field, forgotten a lot of organic chemistry as well. Might guess that carbonates, if any, e.g. calcium carbonate in milk would react with acids to release CO2 gas, may push liquid up, reflex takes over. But would also be a factor in milk with soft drink. My last on this tangent.
Regards

 

[azg]

Mine too. Sorry about the unpleasant memories :~/

 

[chemenco]

With soda in plastic bottles you are concerned with the &quot;permeation rate&quot; of CO2 thru the plastic wall. The permeation rate is = solubility x diffusivity, or P=SD. A balloon goes flat quickly when you blow it up my mouth because the CO2 is soluble in the balloon rubber. When the coke is put in the two smaller bottles, there is no CO2 dissolved in the plastic, and the coke goes flat because the plastic absorbs the CO2. With the larger bottle the CO2 is already at equilibrium with the plastic bottle wall in terms of solubility. The flat coke tastes bad possibly because plastic monomer dissolves in the coke. Monomers are frequently carcinogenic - like vinyl and acrylic monomers

 

[JOM]

Milk in the stomach curdles - turns into a cottage cheese. That's the acid at work. The fats in milk will absorb alcohol and hold onto it for some time. It's a good plan to have fatty food in you before imbibing. Without the fats, the alcohol goes straight to the blood.

Is this the longest-lasting thread in the Chemical Engineering forums? You don't know where a question will lead. Cheers,
John.

 

[azg]

John, I think it (at least one of). Probably because on most other threads, a person would receive a satisfactory response and go on back to work. Here it is just a way to talk about serious issues with a smile.

 

[SteveBzzz]

chemenco,

Do you mean that the CO2 is actually absorbed into the plastic itself? If so, how would glass react?

Steve

 

[donmackenzie]

SteveBzzz,
Yes, the CO2 actually dissolves in the plastic, and over time it diffuses through to the outer surface and is lost. Given enough time, all the CO2 will be lost in this manner. CO2 is lost through plastic bottles more rapidly than through glass because the solubility and diffusivity of CO2 in glass are less than in plastic.
I don't have the numbers in front of me but I suspect that due to the relatively low solubility of CO2 in plastic (compared to cola), and more importantly the low mass of plastic relative to that of the cola it holds, that this is not a major contributor to the loss of CO2.
Any thoughts anybody?

 

[25362]

If not CO2, could the caffeine -added to all cola drinks- have any effect when transferring cola from one bottle to another ?