To become the raw material we are familiar with, cork must be extracted from the cork oak. The process involves removing the cork from the tree without having to fell it. This process is known as the cork harvest or bark removal.
Harvesting cork relies on a time-honoured set of skills that must comply with many rules.
When is the cork harvested?
So as not to damage the tree’s ability to regenerate its bark, or even kill it if the wrong techniques are used, cork is extracted during the tree’s active growth season. Hence, the cork harvest takes place between mid-May and the end of August.
A latent period lasting at least nine years between harvests is required to that the bark reaches the right thickness.
As a cork oak lives for approximately 150 years, this means that each tree can be harvested twelve or up to fifteen times.
How is the cork harvested?
In addition to the season and the requisite rest time, the cork harvest requires a high level of expertise. Skilfulness is of the essence.
Cork harvesters must avoid killing the tree by damaging the vessels that provide it with sap. They therefore handle their axes with a lot of care and precision. They often have substantial experience in carrying out this tricky procedure.
To harvest the cork, they methodically follow four steps :
- Split the bark lengthwise to open it up. The edges of the future planks are thus defined ;
- Separate the cork from the inner bark, i.e. the layer that protects the wood ;
- Make a horizontal cut this time to carve out the plank of cork ;
- Delicately remove the cut plank straight from the tree.
The different types of cork oak harvests
Throughout its life, a cork oak is harvested several times. Depending on the age of the tree, the cork does not have the same characteristics.
The first harvest is carried out on trees between 25 and 30 years old. The cork extracted is male cork that is not designed to be used for producing cork closures. As it is particularly hard and irregular, it is used for insulation purposes or for flooring.
The second harvest takes places nine years later. This harvest produces the first reproduction cork. Although not as hard as cork from the first harvest, its quality is still not sufficient for it to be used to produce closures.
The third and following harvests always take place at intervals of at least nine years. This time, the cork – referred to as ‘female’ – is regular and therefore suitable for producing closures.
The cork harvest therefore requires patience and dexterity. Seasoned cork harvesters capable of handling an axe in such a way that it does not damage the cork oak are needed. As the cork can only be harvested every nine years, it is essential that the trees be properly cared for. Lastly, not all cork can be used as the raw material for producing cork closures. Only the female cork is of a high enough standard.