There is a tremendous variety in the quality of the cork that is harvested from the cork oak trees and sorting these different qualities of cork is a key part of the cork industry. Natural cork stoppers are made by taking a strip of cork bark and literally punching out a cork and to make a high quality cork it needs to be as smooth and unblemished as possible. Cork bark is naturally uneven with holes and crevices, but the higher quality the cork bark, the fewer it will have.
So processing cork is heavily focused on sorting the cork bark into high quality which is mainly used for premium natural wine corks and natural bar-top corks, medium quality which can be used for lower quality stoppers and some other decorative products and low quality which is generally granulated for a cork granules supplier to make agglomerated cork products.
Whilst cork trees in certain areas of the world will generally produce higher quality cork because of the local climate, soil conditions and age of the trees (for example the south of Portugal is know for producing the best quality cork in the world, whilst Asian cork is generally the poorest quality), there will be significant variety of quality of cork even from the cork harvested from one particular tree or course from neighbouring trees.
However, cork harvested from a particular forest will average out at a particular quality and will be harvested during the Summer; at the end of the Summer the cork factories will go to the forests to buy all of their cork requirements for the next year and the price will be determined chiefly by the quality (but also of course by demand).
The premium quality cork then has to be sorted manually and it is trimmed to remove lower quality elements, so that it can then go to produce high quality natural corks. The best corks are still produced by hand with a worker examining the strips of cork and working out the best place to punch out a cork (so avoiding any imperfections in the surface of the cork). Further to this the corks are then sorted by laser and then sometimes by hand again.
For a cork producer to make any money it is crucial that they extract the maximum value from the cork that they buy – whilst every part of the cork bark can be used, the high quality parts can be worth 10 times the inferior ones, so an enormous effort has to be made to sort the cork, which is one of the most time consuming and costly parts of cork processing. Much of this process still relies on the experience and training of the workers whose job it is to identify, sort and trim the cork (which is still done with a sharp knife in many cases).
Portugal produces 70% of the world’s cork and most of the expertise in processing cork resides in Portugal with the highly skilled workforce and know-how of all those involved in the cork industry from the cork forests, to the cork buyers, to the cork quality sorters, the cork processors and the quality control and lab technicians.