Questions on carbonated beverages

Factual Questions
1

I did a search on this topic, but couldn’t find anything on the website, so here goes:

My grandfather-in-law and I were having a conversation yesterday about the nature of things and carbonated beverages came up. He wanted to know why warm sodas are flat while cold sodas are fizzy. My explanation was that gases dissolve more readily in cold water vs. warm water. However, I wasn’t exactly sure why. First of all, was my answer correct and if it is, what is the mechanism behind it?

The other question is: why do sodas, warm or not, get explosively foamy when shaken?

Thank you in advance for helping to solve these burning questions.

2

Well actually a things dissolve more easily into a warmer substance. Part of the phenomenon is based on that. The colder the pop, the more it tends to force the Carbonation out, giveing a bigger fiz. But to be honest I doubt the effect is really that big. I think the cause factor here is time effecting both the carbonation content and the temperature of the pop. When you take the cold pop and open it, it is both cold, and at it’s highest concentration of carbonation. But as time passes it loses cool(gains heat) and loses carbonation as it works its way out. If you open a hot can of pop it will be well carbonated, and if you have an open can of pop in a refridgerator if will loose its carbonation(When I was a little kid my mom wouldn’t let me drink a whole bottle of pop at once, so she made me drink half of it, then put one of those stupid rubber tops with the metal holder on the bottle, and put it in the fridge till the next day, but the damn things never sealed, so I know a lot about drinking cold flat pop. :frowning: )
As to the other question. The Carbon Diozide molecules are lighter than the liquid so have a basic tendancy to want to float to the top of the liquid and out. However when a can is basically stable, the liquid molecules around them trap the pretty much in place. When you shake the can all of the molecules are moved around. The CO2 molecules that was trapped in the equilibrium suddenly finds a hole in which to escape and head to surface. So many CO2s are now escaping that some of the liquid molecules are now trapped among them going up, causing the foam you see.

3

“Carbon Diozide” is of course my pet name for the substance most people call Carbon Dioxide" :slight_smile:
P.S. Do a search for a Cecil article on Nucleation points.

4

Solubility of GASES in water decreases with increased temperature. That’s why there is so much animal life in the polar oceans - there’s more oxygen in the water than at the equator.

Here’s one explanation:

http://antoine.fsu.umd.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml

5

>> The colder the pop, the more it tends to force the Carbonation out

PLEASE! Do not post stuff you are just making up as it is bound to be dead wrong! This is basic stuff!

There are two things which make carbonated beverages foam (expel the CO2): warmer temperatures and dissolved air. In the manufacture of carbonated beverages the temperature is lowered and dissolved air is extracted. I have explained this is earlier threads so you can do a search for a more complete explanation.

When you shake a soda the main thing is you are dissolving air. The temperature does not change that much.

A soda is “flat” when it has lost the carbonation, regardles of temperature or other factors. I have been served flat, cold, beverages.

6

::Wipes off Chemistry degree and teaching certificate::

First, let me reiterate the correct information that cold liquids are able to dissolve more gas than warmer liquids. Sailor and kalashnikov correct in this and wolfman is incorrect.

Further, Pressure is more a factor in gas solubility than temperature. If you wanna dissolve gas in a liquid, increase the pressure over the liquid. This gives you more of a solubility increase than lowering temperature. Actual numbers depend on the liquid and the gas, along with pressure and temp.

What causes the foaming in opening soda is more a pressure drop than temperature. Of course, the amount of CD dissolved in soda at high pressure vs. low pressure will change with temprature.

7

Spritle, you are correct, of course, but pressure is atmospheric pressure once you have opened the can and that is a given.

Experiment: Open a cold bottle of soda. It loses some carbonation due to pressure drop. Let it sit quietly for 30 seconds. It loses some more carbonation slowly. Now shake it, thus dissolving air. Now suddenly you lose a lot of carbonation. This is due to the oxigen dissolving and not to any change in pressure or temperature.

But to answer the OP: Cold sodas have carbonation because you just opened it from the fridge. Warm sodas are flat coz you let them sit around open for several hours. An open soda in the fridge will also go flat (although more slowly).

8

Now who’s making stuff up? Are you saying that in my can of cola that has 15 PSI CO[sub]2[/sub] above atmospheric that the little tiny space above the soda is air?

I don’t think so. Shaking it merely provides tons of nucleation sites for the CO[sub]2[/sub] to come out of solution faster. You can get the same result by sprinkling salt, or even sand, in your soda.

Try this experiment:
Shake two cans of soda vigorously. Open one immediately, note foam explosion. Let one sit for even just a minute, open it - no explosion. You can’t convince me I’ve changed the concentration of dissolved gas in this cola just by shaking it in the same sealed can its been in for a month. All you’ve done is provide nucleation sites.

9

The air inside the can of soda is of higher pressure then atmoshperic. You can see for you self by tryingto crush the can while sealed and then when open.

It would make sense that shaking the can will provide nucletion sites to aid in the relaese of CO2.

Also if you take a well cooled and not shaken can (unopened) - and feal the pressure by trying to crush it - then give it a good shake and again try to crush it you might be able to tell if the pressure increases.

10

douglips, as I menationed in other posts, I have worked selling and installing machinery used in the manufacture of carbonated beverages and, believe me, I know what i’m talking about. In the manufacture of carbonated beverages your problems in this order are: (1) Foaming at the filler, (2) Foaming at the filler, (3) foaming at the filler (then you have Brix deviation and other stuff but, believe me, foaming is #1, 2 and 3 all together).

Dissolved air is a major cause of foaming and getting rid of the dissolved air by scrubbing is a major part of successful filling without foaming. In fact, it is Oxigen that causes the problem, nitrogen does not cause so much of a problem. I have had some experience with foaming problems due to poor oxigen scrubbing.

So when you shake a can, the #1 cause of foam is oxigen dissolving and forcing the CO2 out. Anybody who has worked in the manufacture of carbonated beverages can explain this to you. If you disagree I would like to know your experience in this field.

11

I don’t see how this follows from your explanation. I’ll take your word that oxygen will cause foaming, but it sounds like the manufactuers take pains to avoid oxygen from getting in the can in the first place. Are you saying that what once the soda is canned, oxygen will come out of the soda and be trapped in the air space?

In addition, gas in the air space and dissolved gases should be in equilibrium, and I don’t see how shaking the soda will cause even more gas to dissolve.

Is the nucleation site explanation completely bogus? If you had a sealed bottle with only soda and pure CO2 (no gaseous oxygen), shaking will not cause foaming at all?

12

I have explained the manufacture of carbonated beverages before so I’ll be very brief: Water is treated to sterilize it, then, still warm, it goes into a scrubber to remove the air. This is a tank with a vacuum where the water is sprayed in a fine mist. Having removed as much air as possible, the water is now chilled. It is mixed with the syrup carefully measured to ensure correct output brix. (You realize the syrup has its own set of problems, dissolved air being one of them.) Now the beverage is carbonated by injecting the CO2 and the carbonated beverage goes to a storage tank. That is the end of the manufacturing process. From here it goes to the filler which has a central tank. Up until this point, since the water was scrubbed of oxigen, it has not been in contact with air again. The tanks are all filled with CO2 and the whole thing is under pressure.

The tank of the filler is also under pressure and topped with CO2. The filler goes around at great speed. The container (can or bottle) is placed under the nozzle, pressure is equalized, filling starts, when the container is full, filling stops and, as the container leaves the filler for the machine which will put the top (of the can or bottle) pressure is removed and the container is open to the atmosphere. This process moves extremely fast and the containers are shaking around. Any air dissolved in the beverage is going to cause foaming and air is about the only thing which will cause foaming (well, and high temperature). Air gets into the beverage while filling mainly but also maybe by insufficient scrubbing, the beverage (or sometimes, it seems, magic).

The point here is you want to fill (I)as fast as you possibly can (II)at the highest possible temperature (saves a lot of energy (=$), (III)while avoiding foaming.

I was in charge of the machine which manufactures the beverage but the filler was from another vendor. When we had foaming problems (i.e. every day) I generally thought the problem was with the filler while the filler guy usually thought the problem was with the beverage I was sending him. When you start having problems the first thing is to slow down the filler as a filler might be able to fill 100 bottles a minute and will foam like crazy at 150 BPM.

So, you see after filling but before capping the container is (I)open to the atmosphere and (II)shaking around a lot. When it is capped you can be sure there is a lot of air in there.

As I said, oxigen dissolves in water much more readily than CO2 and will displace it.

Note that during the entire manufacturing process the carbonated beverage is moving around and being shaken much more than you can shake it in your hands. Yet, in the absence of dissolved air, the carbonation stays long enough to cap the bottle. With any dissolved air the beverage foams explosively to the point where you may lose most of the beverage before capping.

In the total absence of air, (supposing only CO2 in the bottle) if you shake it I would imagine the pressure would rise but nothing compared to what happens with air, even if not much.

I have also mentioned: Most bottling plants can be visited by the public. Call your local Coke or Pepsi bottling plant and ask them when you can take a tour. They’ll be happy to show you all this, treat you to a sample of their products and give you a pen and a baseball cap with their logo. :slight_smile:

13

Some more information on the volatility of carbonic acid in the presence of water:
http://newton.dep.anl.gov/askasci/chem99/chem99661.htm

14

I would guess that CO2 gas trapped (through shaking) in the liquid can act as a nucleation site too. You just need something diffrent in there.

15

Thanks for the explanation sailor. One thing I’m still not sure is, if gaseous oxygen and dissolved oxygen sit together in a can for a while, they should reach an equilibrium. Why would shaking the can upset the equilibrium and cause more oxygen to dissolve? You are merely increasing the surface area, which will make the system reach equilibrium faster if it wasn’t there already. But I don’t think it will change what the equilibrium concentration is.

16

scr4, that is a very good point. I am really not an expert in chemistry so I should let someone who know more give you an answer. In the meanwhile let’s think about just a solution of air and water at atmospheric pressure…

Take a bottle, half fill it with water and shake well. This water has a lot of dissolved oxigen. If you let it sit the oxigen content will gradually decrease. Shake again and it will increase again. Why? I have no good explanation. On the one hand it makes sense. On the other hand your argument, which says the concentration should not change, also makes sense to me…

Note that water in rivers contains more oxigen because it is agitated. Fish bowls have air pumps to dissolve air in the water. Your point would contradict this… anyone?

17

Fish bowls have fish to convert oxygen to carbon dioxide. Rivers are dynamic systems including lots of life. In a sealed container, the solution of gas must eventually reach equilibrium.

I’m not contesting your assertion that oxygen drives out CO[sub]2[/sub], I’ll leave confirmation/rebuttal to someone willing to look it up as I don’t know off the top of my head. However, I do contend a) little if any non-CO[sub]2[/sub] gas is in a sealed soda can b) shaking a sealed can doesn’t change the concentration of dissolved gas, and c) it’s the nucleation sites that matter in a sealed can.

18

Shaking the can will have only a tiny effect on the equilibrium between gaseous and dissolved CO2. You ARE adding mechanical energy, so the effect is not quite zero. What shaking will do is cause the formation of zillions of tiny bubbles which, when the equilbrium is shifted by opening of the can, serve as nucleation centers for zillions of larger bubbles. As sailor says, the identity of the gases in the can have a strong effect on the violence of the foaming when a can is opened. Particles suspended in the liquid can also have a powerful effect. I recall seeing a periodic table of the elements produced by the Carlsburg brewery (~1950’s vintage) that indicated the propensity of each element, to contribute to the wild foaming of beer when opened. Apparently powdered carbon, used for filtering, can have disasterous effects if it makes its way into the final product.

19

Thanks everyone, for the replies.

Actually, my (and my grandpa-in-law’s)observation has been this: I have a room temperature can of coke and a refrigerated can of coke. I pour each into a clean glass, also room temperature. The cold can of coke is fizzier than the warm one. Neither can has been sitting around open for any length of time. Is the cold can actually fizzier? It certainly seems that way.Or is my perception somehow distorted?

I have tried to do a search for “nucleation site”, but couldn’t find it. Is it older than 2 years? I have also tried searching under “soda can,” “coke can,” “soda foam,” what have you, but nothing has come up.

20

When you say “fizzier” do you mean that it bubbles more when pouring, bubbles more as it sits in the glass, or tastes fizzier on the tongue ?

The warm can should bubble more during pouring (higher temp-> faster gas exchange), less after it sits in the glass a bit (it’s moved farther down the path to equilibrium with the atmosphere), it might taste more or less “fizzy” in the mouth depending on the temperature differential between glass and mouth, and how much CO2 remains in the pop before it is drunk.

The term “Nucleation site” has been around for ages. When something starts happening in an apparently uniform system it usually starts happening at a point which is slightly different than the rest of the system.
When the process involves growth of bubbles, crystals etc. this place at which the process starts is called a nucleation site. Physical things like bits of dust, tiny bubbles are frequently all that’s needed to create a nucleation site, but temperature gradients, small currents etc. can serve as well.