Science Questions

Why do they use CO2 in fizzy drinks?

Sun, 4th May 2008

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Question

Paul asked:

Why do they use CO2 in fizzy drinks? Couldnít you use nitrogen instead?

Answer

There are a number of reasons for this. One of them is that carbon dioxide dissolves really quite well compared with nitrogen. Nitrogen will not dissolve. Itís very insoluble, you have to make nitrogen work quite hard to dissolve and thatís why when you get the bends after you surface quickly from diving itís the nitrogen that bubbles out of your blood and causes the bends because it just doesnít want to dissolve. Carbon dioxide does. The other thing that carbon dioxide does when it goes into water and one of the reasons it dissolves quite well is it reacts with water to make carbonic acid. So CO2 plus H2O goes to H2CO3, thatís carbonic acid and that dissociates into H+ (thatís the acid bit, the hydrogen ions) plus HCO3- bicarbonate. When you have acids in a liquid acids taste liquidy. So you get this very nice lemony flavour added to the drink so the carbon dioxide not only dissolves well so you can get your drinks really fizzy and get your gasses in it also means it tastes nicer and you can get lots of gas dissolving so it comes out gently in the drink. It stays fizzier for longer. Also itís free. You can get it from the brewing industry, yeast produces it and you donít even have to purify it. You can just get it off the yeast.

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