I just returned from tens days in Portugal and spent several days in Alentejo, walking in some old cork oak forests. Alentejo is in south central Portugal and is where the majority of the cork trees are farmed.
Once the tree is planted, the first harvest is twenty five years later. This first harvest is the “virgin cork”, the same type that is used for mounting plants. The bark is thick, rough and uneven. The bark is then harvested every nine years. The second harvest is less rough, but not acceptable for cork stoppers. This harvest is ground up and used for other production such as flooring. It is not until the third harvest, (the tree is now 43 years old) that the cork quality is the type that can be used for making cork stoppers.