Science Questions

Why do they use CO2 in fizzy drinks?

Why do they use CO2 in fizzy drinks? Couldn’t you use nitrogen instead? Paul

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. It’s very insoluble, you have to make nitrogen work quite hard to dissolve and that’s why when you get the bends after you surface quickly from diving it’s the nitrogen that bubbles out of your blood and causes the bends because it just doesn’t 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, that’s carbonic acid and that dissociates into H+ (that’s 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 it’s free. You can get it from the brewing industry, yeast produces it and you don’t even have to purify it. You can just get it off the yeast.

May 2008