Why does gas escape when a bottle of ginger ale is opened?

Ginger ale is a beverage that generally contains as its
ingredients ginger, sugar and carbonated water. Some brads of ginger ale may also
contain other spices or fruits to impart a unique
flavor.

Carbonated water contains carbon dioxide dissolved
in water. At normal pressures the solubility of gases in water is very low. To dissolve
gases in water, the pressure that is relevant is that just above the liquid surface. At
high pressures, the gas molecules are pushed into the water and forced to remain
dissolved. When the pressure is decreased the molecules escape from
water.

A bottle of ginger ale is tightly sealed and has a
very high pressure inside which forces the carbon dioxide gas to remain dissolved. When
the bottle is opened, there is sudden drop is pressure. This makes the carbon dioxide
escape in the form of a foam that is seen when bottles containing carbonated drinks are
opened.