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

 

[aspearin1]

Well it seems you thought of most everything, and it's an interesting question. Some possibilities might include the disturbance of even gentle pouring and contact with air. You say you pressurized each container as well so it should not be a matter of head space so much. Your glass bottles, I assume they were clean. If you used a detergent that is mildly basic, as many are, residuals on the glass could buffer the cola, and actually neutralize the carbonic acid. Just a thought. Could be a possibility.

 

[SteveBzzz]

Interesting,

Well, all of the bottles are plastic with extensive rinsing and no soap residue. Regarding the possibly of the slightest amount of disturbance to effect the carbonation, I do not think that this is an issue. All 3 samples experienced an insignificant amount of disturbance (2 receiving, 1 pouring). Also, I have a feeling that even if I was able to transfer the cola with zero disturbance, that the results would be the same. As far as pressurization is concerned, I did not pressurize the bottles myself. They pressurized themselves through the expansion of carbonation after the bottle was sealed. Interesting though, that after sealed for 2 hours, the smaller bottle was under higher pressure than the larger bottle, but yet the lower pressure, larger bottle had more carbonation. There is one other variable that I can think of. Maybe there is a relationship between pressure, capacity of bottle, and amount of liquid. The small bottles were filled to about 95% capacity, while the 2.0L bottle was 50% filled before resealing the bottles, and awaiting testing. Hmm...I have to do more experimenting...

 

[rbcoulter]

There are some other factors here.
What were the final temperatures in all the bottles?
Heat will drive the carbonation (CO2) out of the liquid.
From your description it appears that this happened to a greater extent in the smaller bottles because they tasted flat and there was more pressure in the head space.
1 liter will stay colder (less heat transfer area per volume) than 0.5 liters.

 

[isofuncurves]

Are you actually measuring the pressure in the two bottles or just performing a squeeze test? The larger bottle generally feels softer because of its geometry...hmm I have a couple 0-20 digital pressure gauges in my garage. Did you try having a spare 2L bottle and transferring the remaining 1L bottle that has been cleaned and prepared the same way as the smaller bottles? This might rule out cleaning and transfer effects.

The pouring process may be highly effecient at mass transfer because of the relatively large survace area as the small stream of fluid is transferred from one bottle to another...no fizzing but high diffusion rate and loss of CO2?

The apparrent higher pressure in the small bottle? An illusion? What causes the bottle to become pressurized at all? I'm guessing... The partial pressure of CO2 in the headspace is initially very low but CO2 in the soda is high(er); this is the driving force so the pCO2 in the headspace increases. Since the headspace is smaller the pCO2 can equalize faster. The CO2 transfer rate might be higher in the large bottle but equilization takes much longer.

To test...do the pressures equilize at t=long time? Large bottle may be even higher at t=long time since no losses from transfer.

What does everybody think?

Carl

 

[JOM]

SteveBzzz,

What about Pepsi? How does that peform?

Seriously, why not try this-

Take two 2L full bottles at the same temp. Open one and empty, leaving a clean bottle (don't rinse). Open the other and pour half into the empty bottle. Recap both and see what pressures develop and do the taste test.

If there is any difference then it could only be a result of the pouring. I'm sure there's many other experiments to devise to test various theories - lucky it's Christmas time and the beverage won't go wasted. Cheers,
John.

 

[gkandy]

Presume your experiment was with plastic bottles. Carbonated drinks in plastic bottles breathe through the plastic surface. That's why there is a taste difference in cola drinks between a plastic bottle closer to the manufacturing date and one closer to the expiry date. In cans this phenomenon is not significant.

Now the above phenomenon depends upon the surface area / unit volume of carbonated drink . The smaller bottle would have a larger surface area and it will tend to lose more CO2 through diffusion. Moreover , while transferring basically you have agitated the liquid , therby increasing the driving force for this diffusion and hence there is a tendency for more CO2 to escape in the smaller bottle.

Hence the smaller bottle by combination of higher surface area and higher driving force for diffusion happens to lose its fizz faster.

How is this for an explanation !!!

 

[SteveBzzz]

Hmmmmm,

Well, there is a Coke plant about 20 minutes from my house. I guess I could just show up there with my questions and a hidden camera )

OK, Here are my reactions to some of the various questions posed to me.

I did not measure the temperature of the colas because I did not feel it necessary. The cola was cold, taken from the refrigerator, I'm guessing about 45 degrees F. I did not think this to be a factor since all of the samples were drawn from of the same source, and therefore were the same temperature. When removed from the refrigerator a few hours later, I assumed also, that they were of equal temperatures.

I did not actually measure the pressure difference because I did not think I needed the numbers at that point. My observation is this. Initially both small (.5L) bottles were filled to capacity, and the large (2L) bottle is therefore emptied to contain 1L or 50% of it's capacity. After a few hours the bottles were observed and tasted. Before opening the smaller bottles, I observed that they were basically rock hard. I would say that there was a 1-2 ounce gap of space at the top of the bottle when sealed. The larger 2L bottle was under relatively less pressure, because the bottle was able to be squeezed. Could this have something to do with the fact that water can't be compressed? The slightest release of CO2 in the smaller bottles will rapidly increase the pressure because the bottle is filled to 95% capacity with only a small volume of remaining space to pressurize?

I did the cola transfer with extreme caution as not to disturb the soda and cause fizz. However, it is possible that it "invisibly" dissipated during flow? To rule this out, I suppose I could fill a bucket with coke and devise a method to submerge the bottles in the bucket and to fill them in this method in which to eliminate transfer flow loss. Think of dipping a glass sideways in a sink full of coke, and filling it that way. In any case, if there is a carbonation loss, would it not occur equally in all of the samples?

Yes, it does seem that the larger bottle takes a lot longer to achieve the same pressure of that of the smaller bottles, leading me to conclude that there is more CO2 loss from the larger cola sample. But yet when tasted, the Cola from the larger bottle clearly has more gas in it and tastes better.

gkandy, yes you are absolutely correct about the taste differences and gas behavior between glass and plastic. I prefer glass personally.

You stated, "The smaller bottle would have a larger surface area...it will lose more CO2 through diffusion...smaller bottle has a surface area and higher driving force for diffusion...to lose its fizz faster." Did you get that backwards, or is it my bad?

Well, it's going to be a long and potentially costly weekend. I may abandon Coke and Pepsi all together and get Walmart soda!

I will conduct more experiments this weekend. I especially like the one about pouring half of a 2 litter bottle into an empty 2 liter bottle, thus having 2 large bottles that are both half filled.

Wish me luck )

 

[JOM]

Steve,

Your dedication to the pursuit of scientific truth is amazing.

Here's another experiment you might try.

Take two 2L full bottles of Coke. Open both and pour down the sink. Fill one up with tap water. Pour from that one, half its contents into the other one. No, that's the wrong plan. You start with one full 2L and two full 500mL bottles, OK?. Yeah, that's it. Open all bottles and pour contents away. Fill the big bottle with water and then, from that one, fill the two small bottles. Put all bottles in fridge and see what pressures develop. Then you'll see if the "rock hard" condition of the small bottles is a result of the bottle size or the carbonated Coke. Actually, I see now you don't need to buy any more Coke. You must be up to your knees in empty bottles of all sizes by now (and a bloated belly?). Just take some empties and do the original experiment with water. Here's another - you're an adult, right? Find a child about half your size. You each drink quickly 1L of freshly opened Coke. Observe results.

Tis the silly season. Cheers,
John.

 

[SteveBzzz]

I give up.

I'm to tired to continue. First of all, I shouldn't be drinking so much soda. Second, I have a new experiment. Why does chocolate milk have expiration dates that are sometimes two months long, whereas regular milk expires in about a week? When I was young my grandmother used to give us milk that had been stored in the freezer. Unfortunately, I don't remember what it tastes like. I froze a container of milk tonight, and will report back soon as to it's progress. Any ideas?



Happy Holidays

 

[nbucska]

Steve: I would like to know about your project - pse contact me. <nbucska@pcperipherals.com>

 

[jcd3]

Steve -

In reference to your question of gkandy's surface area - he's actually referring to specific surface area. This means the surface area per unit volume. This property would be important if the concern is interaction between the soda and the plastic, as more soda would be in contact with more area of the plastic in the smaller bottle. It's a little confusing, but it makes sense if you think about it for a while. Again, I think this only really matters if the concern is soda to plastic interactions, if CO2 is indeed breathing through the plastic.

Despite possible abandonment of the project, my only other thought is the composition of the bottles... are the smaller bottles the same plastic as the 1L bottle? Different plastics will have different characteristics, which would play a role if breathing is an issue. And I think someone else mentioned it, but the higher pressure you note in the smaller containers is likely due to the partial pressure of CO2. Essentially, if you have two identical volumes of soda at the same temperature, the two volumes would yield the same partial pressures of CO2 above the soda. If you put a volume in a much smaller container, the soda would try to produce the same pressure (for lack of a better way to say it). Essentially, I think the higher pressure you're noticing only comes from the decreased amount of free volume in the container. To check this, try perturbating a full 2L bottle of Coke. The full bottle will likely exhibit the same type of hardness you're experiencing with the smaller containers, as there is a very small amount of free space in the unopened container - it's the reason you hear a hissing noise when you first open a bottle...the gas inside is pressurized and wants to escape.

Anyway, sorry to hear a sufficient answer didn't quite arise from your experiments. Best of luck on the milk thing (you might try to find a biological explanation, rather than chemical, though - expiration dates usually have to do with the spoiling of the milk. Perhaps the chocolate variety allows the addition of extra preservatives that would alter the flavor of regular milk?)

Best of luck!
Jason

 

[azg]

Steve,

I applaud your scientific curiosity. While I agree that the tongue of a Coke afficionado is a very sensitive tool, the first thing to do when doing any research is to make sure your gauges are OK. You need to perform gauge R&R first, in other words get a consilium of 3-5 Coke afficionadoes like yourself and measure their evaluations of the three Coke bottles.

The taste differences are most definitely related to the release of CO2 when you are pouring the Coke from the 2-liter bottle into the smaller ones.


I look forward to hearing more from you! Good luck and happy New Year!
The order in which you are filling these bottles will matter a lot in this experimentation. So when you are designing your experiment make sure you rotate the smaller bottles giving each an equal chance of being the first to be filled.

To minimize that effect, try connecting the source and destination bottles with an airtight hose and setting up an air bleeding valve on the top of the destination bottle. But set up you hose in such a way that your destination bottle would be filling from the bottom, not over the top. It will take some ingenuity, but I am sure you can handle it. That should make sure that you are not introducing the additional effect of gas release due to abrupt expansion.

Also, make sure you distribute the Coke into the smaller bottles in such a way that you do not let air into the source bottle in between the pourings.

 

[SteveBzzz]

Hmmmmmm....

Well, I got a food-saver for Christmas. For those of you who don't know what it is, It's a vacuum bag sealer. You place your food in a special bag, then insert the open end into the machine. Press the button and presto! It sucks all of the air out, and you've got a nicely vacuum-packed meal...or the specimen of some experiment. Imagine, I can do all of the above experiments with various combinations of vacuum combinations.

Happy holidays.

 

[azg]

Steve, be careful about sucking out the CO2 from carbonated drinks: once you apply vacuum to the Coke bottle, you will lose your CO2: the partial pressure of dissolved CO2 in the Coke bottle will become higher than the partial pressure of CO2 in the space above the Coke, and it will want to escape...

On the contrary, when pouring, you want to keep all bottles under the same pressure.

Good luck and Happy New Year!

 

[Railbaron1]

I have a new question for all the Coke experimenters out there.... My first interview question as an engineer was, &quot;Why does Coke fizz more when you pour it over ice than into an empty glass?&quot;

14 years later, I am still searching for a decent answer to this question, but sad to say I have used it myself now just to see what individuals say.

Any thoughts?

 

[azg]

Railbaron, that's a good one! I think it does so because the ice cubes work as packing in a stripping column: they develop the phase contact area, thus increasing the efficiency of this desorber. Try doing it with different ice pieces in shape, size, and order (vs. random) and see how it comes out then. :->

 

[aspearin1]

I think I follow azg's reasoning... on that level, it is also (mid-pour) giving a much higher exposed surface area to the air. Try similar experiments without ice, but rather with a room temperature plastic or glass, to take eliminate the temperature variable.

 

[azg]

That's a good point! Also, ice melts into the cola, which complicates the big picture, as it may alter the solubility product for CO2 in the mix.

BTW, here's another question: which way will ice alter the &quot;fizz&quot; compared to plastic or glass? I wouldn't bet my paycheck on it, but I think it will promote the acceleration of the release of CO2: there is a thin film of water on the ice, and upon contact, CO2 wants to escape, as carbonic acid is formed in the reaction, but it is very unstable, decomposing into CO2 and water.

Any other bets?

 

[SteveBzzz]

Greetings all,

Well, I have more or less stoped wasting...oops...I mean devoting my time to this experiment. However...

Walmart had a closeout sale on rootbeer making kits. It comes with everything you need to make 3 liters of rootbeer and or cola. The process takes a few weeks, so I will keep you posted.

I am going to make a gallon of chocolate milk, using 2% and nestles quick. Why make a glass at a time, when you can make a gallon? I figure at least i'm going to get some protein from this experiemnt.

Steve