When you shake a bottle of fizzy drink, why does it fizz when you open it?

The gas that makes fizzy drinks fizzy is carbon dioxide, which is dissolved in the drink like sugar in a cup of tea. However, while the bottle is on the shelf it gradually leaks out and collects in the space between the bottle cap and the drink – called the head space. Usually when you open a bottle of drink this gas can escape easily and you only hear a slight psssht.

But when you shake the bottle vigorously the carbon dioxide contained in the head space gets mixed up in the drink and forms pockets of carbon dioxide within the liquid itself, which cant easily escape when you open the bottle. Instead these pockets rise rapidly to the top of the bottle dragging some of the drink with them.

This then flows out over the top of the bottle and a fine old mess is created.