Cork harvesting is a timely yet sustainable process. It takes roughly 25 years for cork oak trees to produce usable cork. Each tree trunk must reach a circumference of about 70 cm when measured at a height of 1.3 meters. This ensures that when harvested, the tree will not be harmed.
The first harvest of a tree produces an irregular cell structure and can not be used for cork stoppers. However, it still can be processed into materials such as flooring or insulation. Even the second harvest, 9 years later, is not quite usable. Finally, it is the third harvest that is suitable to be used for cork stoppers. On average, trees can be harvested up to 18 times or for about 150 years.
The Harvesting Process
There are six stages in cork harvesting.
Skilled Descorticadores, or the cork experts, use an axe to make a vertical cut in the trunk of the tree. Depending on the ‘feel’ of the axe, the descorticadores can determine the difficulty in the extraction.
The outer bark is then separated from the inner bark layer by inserting the edge of the axe and twisting.
A horizontal cut with the axe divides the bark into planks to be removed. Caution is taken to not damage the inner bark layer, because this can alter the geometry of the trunk as it regrows.
Once divided, the plank can then be removed from the tree. The larger the plank, the higher economic value it has.
After all planks are removed from the tree, the Descorticadore removes any remaining cork pieces at the base of the trunk in order to rid it of any possible parasites.
At last, the tree is marked with a number corresponding with the year.
After the harvest, planks are stacked outside and exposed to the elements. According to the International Code of Cork Stopper Manufacturing Practice (ICCSMP), these piles must be placed on materials that do not allow contamination or contact with the soil. This process is called the seasoning period, and will be done for a minimum of six months.