The life cycle of cork as a raw material begins with extraction of the cork oak bark. Harvesting takes place during the most active phase of growth of cork, between the middle of May or beginning of June until the middle or end of August.
It takes 25 years for a cork oak trunk to start to produce cork and be profitable. Each trunk has to reach a circumference of about 70 cm when measured 1.3 metres above ground level. From then on, the cork can be harvested from the tree for on average 150 years.
The first harvest, which is known as “desbóia”, produces cork of a very irregular structure which is too hard to be easily handled. This is the so-called virgin cork which will be used for applications other than cork stoppers (flooring, insulation etc.), since its quality is far from that necessary to manufacture stoppers.
Nine years later, the second harvest produces material with a regular structure, less hard, but still not suitable for cork stoppers – this is known as secondary cork.
It is from the third and subsequent harvests that the cork with the best properties is obtained, suitable for the production of quality corks, since its structure is regular with a smooth outside and inside. This is the so-called “amadia” or reproduction cork. From then on, the cork oak will supply good quality cork every nine years for around a century and a half, producing, on average, 15 bark harvests throughout its life.
The harvesting of the cork oak is an ancient process that can only (and should) be done by experts: the descortiçadores. Manual skill and a lot of experience is required to avoid damaging the tree.
Cork harvesting is performed in six stages:
Rest period. After the harvest, the cork planks are stacked in piles either in the forest or in yards at a factory. There they remain exposed to sun, wind and rain. All the piles are constructed taking into account strict specific rules defined by the International Code of Cork Stopper Manufacturing Practice – ICCSMP, so as to allow the cork to stabilise. The piles should be stacked on materials that do not contaminate the cork and prevent contact with the soil. Wood, for example, is expressly prohibited because it can transmit fungi. During this seasoning period, the raw material matures and the cork stabilises. According to the ICCSMP, the seasoning period for the planks should never be less than six months.