Fizzy drinks (carbonated beverages) are produced by injecting carbon dioxide into the drink at a pressure of several atmospheres. Carbon dioxide dissolves readily at normal atmospheric pressure, particularly in cold beverages, but far more so at high pressure and large volumes of gas can be dissolved. When the pressure is released the carbon dioxide comes out of solution forming numerous bubbles and begins releasing the carbon dioxide back into the atmosphere. After many minutes most of the carbon dioxide has been released and the drink is said to be "flat".
The chemical phenomenon whereby carbonated drinks taste fizzy is due to carbonic acid inducing a slight burning sensation, and is only indirectly related to the bubbles- both phenomena are caused by the carbonic acid concentration.
Carbonation can also be produced by partial fermentation in a sealed container. This is the method used in the production of ginger beer and by careful control, and use of appropriate yeasts, the alcohol level can be kept very low.
