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?
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.
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.
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.
N2 is actually slightly more soluble in water than CO2 cite, 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.
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.
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?
Are you sure about that? The wikipedia 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.
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, 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.