Transformation Process
The life cycle of cork as a raw material begins with extraction of the cork oak bark, which is called harvesting. Cork enters the manufacturing process after it is extracted, to produce the myriad of products that we can find: stoppers, construction and design materials, among many others.
Cork Harvesting
Stripping is the removal of the bark from cork oaks and takes place during the most active phase of cork growth, between the middle of May or beginning of June until middle or end of August.
To start stripping, the trunk of the cork oak has to reach a perimeter of around 70 cm when measured 1.3 meters from the ground. This takes about 25 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 known as 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 cork sttopers, since its structure is regular with a smooth outer and inner bark. This is what is known as “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 are required to avoid damaging the tree.
Cork harvesting is performed in six stages:
1.Opening
2.Dividing
3.Separation
4. Extracting
5. Removing
6. Marking
Rest period
After stripping, the cork planks are stacked in a yard and remain there exposed to the open air, sun and rain. The stacks are formed taking into account rules (defined by the International Code of Cork Stopper Practices - ICRP), for a period of no less than six months, in order to allow the cork to stabilize.Industrial Path
Cork Stoppers
Cork goes through a series of stages, from the cork plank to the cork stopper, which depend on the type of stopper to be produced. Natural cork stoppers are punched from a single piece of cork, whereas technical stoppers are produced from a body consisting of agglomerated cork granules, to the ends of which natural cork discs may be applied.
Boiling the Planks
After the stabilization or resting period, the mature cork planks (from the third stripping) are cooked in clean, boiling water. The cooking process lasts at least an hour. The aims of boiling are:
2. Extract water-soluble substances from it
3. Increase its thickness and thus reduce its density
4. Make it softer and more elastic
Before boiling, the cork cells are compressed irregularly, but during this process, the gas contained inside the cells expands. As a result, the structure of the cork becomes more regular and its volume increases by around 20%. Boiling is an operation prescribed by the International Code of Cork Stopper Practice. As well as improving the internal structure of the cork, it also helps to substantially reduce microflora. Several cork stopper companies use complementary processes to achieve better disinfection, while others use dynamic systems where the water is constantly circulating and at the same time being decontaminated before re-entering the cooking cycle.
Stabilization
After cooking, the cork stabilizes. It is only after this period, which lasts two to three weeks, that the boards are sorted. Stabilization serves to flatten the planks and allow them to rest. This is the only way for the cork to obtain the consistency it needs to be transformed into stoppers.
Stabilization also allows the cork to reach the ideal moisture content for processing, which is around 14 percent.
Selecting the planks and rabbeting
The edges of the boards are prepared and the edges trimmed before an initial manual assessment is carried out. The boards are separated into quality classes based on thickness, porosity and appearance.
The cork planks are then cut (rabbeted) into strips slightly wider than the length of the cork stopper to be made.
The cork planks are then cut (rabbeted) into strips slightly wider than the length of the cork stopper to be made.
Construction, decoration and design materials
Cork from the first two harvests (virgin and secondary cork), as well as the cork that is not used for the production of cork stoppers, is used for the manufacture of products intended for construction and other applications, such as transportation, clothing, sports, among others. Composite agglomerates and pure expanded agglomerates are the two main types of products found.
