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View Full Version : Why not use plain old air in soft drinks instead of carbon dioxide?


Arcite
11-23-2010, 10:17 PM
Today I got a Bed, Bath, & Beyond catalog in the mail, which has on its cover an ad for the Genesis Soda Maker, an appliance for making carbonated beverages at home. I thought, "hey, that's pretty cool," until I turned the page and saw that of course you have to keep exchanging CO2 bottles to use the thing.

This got me to thinking. Why do beverage makers use CO2 to make fizzy beverages, when there is a plentiful gas all around us? I know beer and sparkling wine are naturally carbonated by the fermentation process, but we're talking about non-fermented beverages which we're intentionally "fizzing" by injecting gas. Why not just pump in air? Is there some chemical property making it less suitable? (Yeah, it's almost 80% nitrogen, but nitrogen is used in Guiness beer and seems to work just fine.) Are we worried about a fire starting in our stomachs? Is it just cheaper to buy CO2 made as the byproduct of some other industrial process than it is to compress air to the required pressure?

GameHat
11-23-2010, 10:22 PM
Dissolved carbon dioxide in an aqueous solution (e.g., a beverage) gives a very weak solution of carbonic acid.

It's the acid that gives carbonated beverages their "bite" or "tang".

If you want to know why simple aerated beverages are no good, drink a flat soda. If you're still unconvinced, I'll bring you into my lab and we'll bubble some either N2 or compressed air through a flat soda, and it will still taste, well, flat.

It's the acid (weak of course) that's needed to give bubbly drinks their "sharp" taste.

Larry Mudd
11-23-2010, 10:23 PM
Oxidation is unkind to food substances, innit?

Raygun99
11-23-2010, 10:24 PM
They would taste different. CO2 in soft drinks is actually added by adding carbonic acid, which decomposes in solution to water and CO2. But it's what gives Coke (and other soft drinks) that sharp bite which wouldn't happen if you used N2 or another non-reactive gas.

Joey P
11-23-2010, 10:25 PM
This got me to thinking. Why do beverage makers use CO2 to make fizzy beverages, when there is a plentiful gas all around us? I know beer and sparkling wine are naturally carbonated by the fermentation process, but we're talking about non-fermented beverages which we're intentionally "fizzing" by injecting gas. Why not just pump in air? Is there some chemical property making it less suitable? (Yeah, it's almost 80% nitrogen, but nitrogen is used in Guiness beer and seems to work just fine.) Are we worried about a fire starting in our stomachs? Is it just cheaper to buy CO2 made as the byproduct of some other industrial process than it is to compress air to the required pressure?

IIRC, Nitrogen doesn't dissolve into water (beer/soda) very well. That's way Guinness and Youngs (and a few others that use Nitrogen) have a widget. If they just pumped in the Nitrogen it would all come out as soon as you opened the can. The Widgets (either a torpedo shaped thing with a hole in the bottom for bottles or a ping pong ball shaped thing with a pin hole for cans) release the Nitrogen slowly. The torpedo shaped ones have a hole on the bottom. Each time you tilt the bottle to sip it, a little more comes out and into the beer.
I believe, CO2 stays dissolved in water much longer then 'air' and that's why it's used in soda.

Raygun99
11-23-2010, 10:32 PM
N2 is actually slightly more soluble in water than CO2 cite (http://engineeringtoolbox.com/gases-solubility-water-d_1148.html), but it's a much smaller molecule and makes a smaller bubble. The widget is to provide nucleation sites for the nitrogen to help bring it out of solution.

WarmNPrickly
11-23-2010, 10:44 PM
Are you looking at the same graphs that I'm looking at? Your cite seems to indicate that nitrogen is about 100x less soluble than carbon dioxide. That's certainly what I would expect.

Arcite
11-23-2010, 10:46 PM
Dissolved carbon dioxide in an aqueous solution (e.g., a beverage) gives a very weak solution of carbonic acid.

It's the acid that gives carbonated beverages their "bite" or "tang".

If you want to know why simple aerated beverages are no good, drink a flat soda. If you're still unconvinced, I'll bring you into my lab and we'll bubble some either N2 or compressed air through a flat soda, and it will still taste, well, flat.

It's the acid (weak of course) that's needed to give bubbly drinks their "sharp" taste.

I understand what you're saying, but just from memory, I don't perceive carbonated beverages to have a "bite" or "tang." Coke just tastes sweet to me, not tart, and when I drink flat soda, I perceive a difference in fizziness, not taste. What is the explanation for this?

They would taste different. CO2 in soft drinks is actually added by adding carbonic acid

Are you sure about that? The wikipedia (http://en.wikipedia.org/wiki/Carbonic_acid) article says that carbonic acid only exists in solution. How would you isolate it? Boil off the water? That would just drive the equilibrium toward CO2 which would then evaporate.

N2 is actually slightly more soluble in water than CO2 cite (http://engineeringtoolbox.com/gases-solubility-water-d_1148.html), but it's a much smaller molecule and makes a smaller bubble. The widget is to provide nucleation sites for the nitrogen to help bring it out of solution.

I think you read those graphs wrong--N2 looks to be about 100 times less soluble than CO2, which is consistent with the Wikipedia article on Guinness (http://en.wikipedia.org/wiki/Guinness), which says that nitrogen is used because of its lower solubility, allowing the beer to be put under higher pressure without becoming too fizzy, which is what allows the small bubbles to be formed.

Raygun99
11-23-2010, 10:46 PM
I knew that sounded wrong. I blame my contacts (no, really). The point about bubble size and nucleation points stands, though.

wheresmymind
11-23-2010, 11:01 PM
CO2 is used for flavor, because it's cheap, and because it comes out of solution easily in nicely sized bubbles. When it comes to carbonating drinks, not all gasses will produce the same type or levels of fizziness, due to their different solubilities. Think of the difference between the bubbles in a bottle of seltzer water and a Guinness draft. That huge difference is almost solely due to differences in the gas used: pure CO2 for seltzer, ~70% N2/30%CO2 for Guinness. Similarly, N2O is used for whipped cream because it's lipid-soluble, anti-microbial, and has a slightly sweet taste.

GameHat
11-23-2010, 11:02 PM
I understand what you're saying, but just from memory, I don't perceive carbonated beverages to have a "bite" or "tang." Coke just tastes sweet to me, not tart, and when I drink flat soda, I perceive a difference in fizziness, not taste. What is the explanation for this?

Well, as you notice, the primary taste of Coke is sweet. Most sodas do have a lot of HFCS so you are correct in this.

Do you ever drink carbonated mineral water? I myself enjoy Klarbrunn's (http://klarbrunn.com/)

Many carbonated mineral waters have no sugar added. Properly carbonated, they have a "burn" or a "tang" to them. Flat they taste just like water.

Try one - first as it should be, properly carbonated. Then leave one open for a day and take another sip. The taste is very different.

EDIT: Klarbrunn's calls it "Sparkling Water", but trust me, it's carbonated.

njtt
11-23-2010, 11:06 PM
I knew that sounded wrong. I blame my contacts (no, really). The point about bubble size and nucleation points stands, though.

Why would the size of the molecules be relevant to the size of the bubbles?

Also, although I agree that carbonic acid imparts a tang, you could easily get that tang in other ways (citric acid, for example). The reason CO2 is used rather than air is because it is so much more water soluble, especially under moderate pressure.

GameHat
11-23-2010, 11:14 PM
Well, as you notice, the primary taste of Coke is sweet. Most sodas do have a lot of HFCS so you are correct in this.

Do you ever drink carbonated mineral water? I myself enjoy Klarbrunn's (http://klarbrunn.com/)

Many carbonated mineral waters have no sugar added. Properly carbonated, they have a "burn" or a "tang" to them. Flat they taste just like water.

Try one - first as it should be, properly carbonated. Then leave one open for a day and take another sip. The taste is very different.

EDIT: Klarbrunn's calls it "Sparkling Water", but trust me, it's carbonated.

Double edit - you can include all types of Seltzer in my above definition. Seltzer is carbonated, is fizzy, and tastes sharp. When it goes flat, it tastes like regular flat water.

Squink
11-23-2010, 11:57 PM
From an earlier thread: (http://boards.academicpursuits.us/sdmb/showthread.php?t=176937&highlight=dioxide)
Why CO2 ?
CO2 is a good choice for making fizzy drinks, because not only does it dissolve in a liquid, like other gases, but also reacts with water to form carbonic acid, and its ions. Thus the equilibrium concentration of CO2 in the air, vs solution, lies towards more total carbonates in solution than with a ideal, nonreactive gas. If you charged a bottle of Soda with helium, rather than CO2, most of the gas would come out in one great bump immediately upon opening. However, the kinetics of CO2 <->HCO3- <->CO32- are slow (~seconds), so not only do you end up with a lot more potential gas dissolved when you use CO2, but it comes out more slowly.

Rosentredere
11-24-2010, 01:30 AM
From an earlier thread: (http://boards.academicpursuits.us/sdmb/showthread.php?t=176937&highlight=dioxide)

To expand a little on this:
Your average carbonated Water contains between 5 and 7 g of CO2 per litre. Because most of it forms carbonic acid the pH of the water gets lowered from 7-8 to 4-5, which apart from the difference in taste also prevents spoilage from bacterial growth. For the same reason the removal of other gases, especially oxygen, is an important part of the bottling process.

Mangetout
11-24-2010, 03:28 AM
The point about bubble size and nucleation points stands, though.

Don't think so. At least not if you're talking about the ball/capsule-type widgets. Pressurisation of the can forces beer and gas into the hollow widget through a small aperture. When the can is opened, and the pressure released, the pressure inside the widget jets the beer and gas through the small hole. This agitates the rest of the contents, causing the formation of bubbles. I suppose that's nucleation, but it's the jet coming out of the widget that does it, rather than some surface property of the widget itself.

Balthisar
11-24-2010, 07:40 AM
CO2 in soft drinks is actually added by adding carbonic acid, which decomposes in solution to water and CO2.

Do you have any references for this? The only reason I'm not doubting you is because it's perfectly logical that something different might be done on an industrial scale, but in home use and point of sale, CO2 in soft drinks is actually added by adding CO2 to water, which becomes dissolved CO2 and carbonic acid.

Quercus
11-24-2010, 08:53 AM
And of course beer naturally has CO2 because that's what the yeast makes (along with alcohol). Which I assume is where the idea to carbonate soft drinks came from.

Tastes of Chocolate
11-24-2010, 11:52 AM
Double edit - you can include all types of Seltzer in my above definition. Seltzer is carbonated, is fizzy, and tastes sharp. When it goes flat, it tastes like regular flat water.

Not true.
At home, I have an old fashion seltzer bottle. You fill it with tap water, screw on the top and attach a CO2 charge cartridge. I was surprised to find that if I let a glass of the charged seltzer water sit around and go flat, that it does not taste like tap water again. There is a definate acidic tang to the water still.

Sigene
11-26-2010, 12:17 AM
I'm confident that much of the time carbonating beverages on an industrial scale is accomplished by injecting carbon dioxide into the beverage containers. It isn't added as carbonic acid, and it isn't added by action of yeast (remember, I'm talking on an industrial scale).

my citation comes from being intimately familiar with a carbon dioxide plant that regularly ships tanker trucks of CO2 to a very well known macrobrewery.

cmb12
06-03-2011, 08:54 PM
Looking around the web, this was the closes I could find to what I am looking for, so sorry for the thread necromancy: I was thinking today: why isolate carbon dioxide from sodium bicarbonate or whatever they use industrially? Why no just use air? Nitrogen and Oxygen are at least two orders of magnitude less water soluble than carbon dioxide. It seems like a waste. I mean, I guess they would have to pump a couple hundred or so times as much gas into the liquid since its only trace in the atmosphere, but that still seems way cheaper than making pure carbon dioxide. Anyone know?

Absolute
06-03-2011, 09:13 PM
Looking around the web, this was the closes I could find to what I am looking for, so sorry for the thread necromancy: I was thinking today: why isolate carbon dioxide from sodium bicarbonate or whatever they use industrially? Why no just use air? Nitrogen and Oxygen are at least two orders of magnitude less water soluble than carbon dioxide. It seems like a waste. I mean, I guess they would have to pump a couple hundred or so times as much gas into the liquid since its only trace in the atmosphere, but that still seems way cheaper than making pure carbon dioxide. Anyone know?
The key is to inject the carbon dioxide into the liquid and then seal it before the CO2 can come out of solution. This is only made feasible by getting the CO2 in quickly, meaning you need a small volume of highly-concentrated CO2.

Francis Vaughan
06-04-2011, 12:25 AM
Industrial scale manufacture of basic carbonated water is done by spraying atomised water into the top of a large vessel that is filled with pressurised CO2 and pumping the accumulated carbonised water out of the bottom. CO2 is pumped in to maintain the pressure as the water absorbs the gas. The large surface relative to volume of the tiny water droplets allows the CO2 to be absorbed quickly.

For carbonated drinks this is simply added to the appropriate syrup concentrate. Instant well known soft drinks. Point of sale postmix machines add the syrup at the tap, and thus have a set of syrup containers and a single large supply of carbonated water.

thelabdude
06-04-2011, 12:33 AM
Seems to me I remember CO2 tanks where soda is sold.

Fish Cheer
06-04-2011, 02:37 AM
I knew that sounded wrong. I blame my contacts (no, really). The point about bubble size and nucleation points stands, though.It's only half your fault. Changing the Y axis scaling like that is crazy. Mistakes like yours are bound to happen if you do that, and people should know better.

ETA: Oops, didn't check the date. I guess you're over it by now.

Francis Vaughan
06-04-2011, 03:53 AM
Seems to me I remember CO2 tanks where soda is sold.

Yes. Sorry I was writing at cross purposes. On an industrial scale - say at a bottling plant you have big carbonation devices, mix in the syrup and then can or bottle the result.

A postmix machine has a source of carbonated water and adds the syrup at the moment of delivery of the drink. In this case the carbonation is done inside the postmix machine with an external bottle of CO2. The production rate of carbonated water is much lower, but enough to feed the machine. The critical part of a carbonator is a pump that pressurises the water supply before the CO2 is added.

Also, if you have premixed carbonated drinks (including beer) in large containers (i.e. kegs) it is usual to pressurise the system with CO2. This can be used to force the liquid through the system without the need for pumps, and also maintains full carbonation of the beverage even when the keg is almost empty.

Francis Vaughan
06-04-2011, 04:07 AM
Oh, another issue with CO2 sources. It needs to be very pure. Ordinary industrial CO2 will contain various contaminants. At much too high a level for use in a beverage. This isn't just a health question, but many contaminants will affect the taste. So you get food grade CO2.

For pressurising beer systems you can run into trouble with pure CO2 - it will continue to dissolve in the beer and eventually result in a beer that is too carbonated. A mix, typically called "beer gas" of CO2 and Nitrogen is used to avoid this.

kanicbird
06-04-2011, 07:41 AM
I thought coke was one of the few soda's to use and have on it's label phosphoric acid instead of carbonic acid, making it ideal for cleaning chrome bumpers and the like.

Chronos
06-04-2011, 04:16 PM
In addition to, not instead of. All carbonated drinks contain carbonic acid.

tallcoldone
06-06-2011, 01:03 PM
Not true.
At home, I have an old fashion seltzer bottle. You fill it with tap water, screw on the top and attach a CO2 charge cartridge. I was surprised to find that if I let a glass of the charged seltzer water sit around and go flat, that it does not taste like tap water again. There is a definate acidic tang to the water still.

When you attach the CO2 cartridge and pressurize the bottle, much more CO2 is let into the bottle that can dissolve in the water at ambient pressure. As long a the bottle stays closed, the higher pressure forces excess CO2 into the water. Open the bottle to relieve the pressure and all the excess CO2 comes bubbling out. When the bubbling stops there is still some CO2 dissolved in the water as carbonic acid, more than there was in the water originally. This is the "acidic tang" that you mention.

Balthisar
06-12-2011, 09:52 PM
Oh, another issue with CO2 sources. It needs to be very pure. Ordinary industrial CO2 will contain various contaminants. At much too high a level for use in a beverage. This isn't just a health question, but many contaminants will affect the taste. So you get food grade CO2.
Dirty secret: most industrial CO2 is food grade. I source CO2 for large-scale manufacturing as part of my job. The purity is the same. For my personal use the local AirGas store sells the same.

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