How is soda pop carbonated?
(Lansing State Journal, October 7, 1992)
There are three main ingredients in soda pop: water, syrup and carbon dioxide gas. It is the carbon dioxide gas that is responsible for the fizziness.
When the ingredients are combined, the carbon dioxide gas, syrup and water form a solution. The ingredients are mixed in a container and the empty space at the top of the container is filled with carbon dioxide gas. The bottle or can is then sealed. The carbon dioxide at the top of the container is under pressure and prevents any of the dissolved carbon dioxide from escaping the solution.
When the bottle is opened, a familiar hiss is heard and the carbon dioxide gas in the top of the bottle is released. The dissolved carbon dioxide can now escape solution; the result is the familiar bubbling carbonated drink.
When a partially emptied bottle is recapped, more space is available for more carbon dioxide gas to escape solution, and the remaining liquid in the bottle become more flat. Because pressure cannot build up above an open bottle or cup, the soda in it will go completely flat within in a few minutes.