The first crop, known as virgin bark, is cut when the tree is 25 years old. The trees can be stripped for cork every nine years for a period of 200 years. The older the tree the more cork it produces. Cork is used to prevent oxygen from getting to and spoiling the wine. It can be compressed and when the pressure is released it will swell and make a seal so it makes a good interface between glass and the outside surface.
Corks come in all different sizes.
Long or short, a good cork is the finishing touch to a fine bottle of wine.