Cork is the bark of the cork oak tree (Quercus suber L), a very unique tree with a long life time and an enormous capacity for regeneration. Once the tree reaches a mature age of 25 it is ready to be peeled off for the first time. The first two harvests of cork bark are called the virgin cork and secundeira cork. The quality of obtained material is not good enough to produce cork stoppers. Only at 43 years of age cork oak bark regenerates with the top quality cork called amadia. With each harvest cork is acquiring a smoother texture. It is composed from a honeycomb of microscopic cells filled with an air-like gas and coated mainly with suberin and lignin. Other compounds are identified in its chemical composition, although in less quantity, such as polysaccharides, ceroids and tannins. A single cubic centimeter of cork contains almost 40 million cells – around 800 million in a single natural cork stopper.
Cork harvesting is the process of removing the bark off the cork tree. Specialized professionals use a machete to slice the bark into sections and then they use a metal wedge to peel these sections from the trees. Harvesting takes place always between May and August, when the tree is at its most active phase of growth and it is easier to strip the bark without damaging the trunk. An average cork oak tree can live up to 200 years what gives an opportunity to strip the bark around 16 times with 9-12 years interval. From all the cork oak forests, approximately 340 000 tonnes of cork are harvested each year.
Cork tree forests (Montados) cover the surface of almost 2.2 million hectares in the West Mediterranean basin. These trees are characteristic of this region, and they represent one of the best examples of the development of the multi-functional forest. This landscape supports a rich diversity of wildlife, including the Iberian lynx, imperial eagle and Barbary deer. The cork forest serves a valuable ecological function by providing soil conservation, clean water renewal, while also buffering against climate changes and desertification. It is estimated that every year cork oak forests retain up to 14 million tonnes of CO2, a sizeable contribution to reduce greenhouse gas emissions, the main cause of climate changes.
Equally surprising is the fact that the cork oak increases its ability to absorb these gases during the natural regeneration process following stripping – a stripped cork tree absorbs, on average, five times more CO2. The ability to retain carbon dioxide is also passed on to manufactured cork products, which continue to ensure this function to absorb CO2.
Cork forests are supported by “World Wildlife Fund”
Portugal – worldwide leader in cork sector
Portugal, which has 1/3 of the total area of cork oak trees (34%), is the largest producer of cork, being responsible for around 50% of the world’s cork production. Here, the cork oak is the National Tree and occupies 22,5% of the national forest area. Portugal is not only exporting cork (around 65% of world´s cork export) but also importing, mostly from Spain. Cork represents more than 30% of all forest products exported and 2% of all exported goods.
Data provided by APCOR
Properties of cork
Over 50% of its volume is air, which makes it very light – it weighs just 0.16 grams per cubic centimeter and can float.
Elastic and compressible
Thanks to flexible cellular membranes cork can be fitted against the wall of a bottle under pressure and when released bounces back to its original form.
Impermeable to liquids and gases
Suberin and ceroids contained in the cork cell walls makes it practically impermeable to liquids and gases. Its resistance to moisture enables it to age without deteriorating.
Thermal and acoustic insulator
Due to gaseous components contained in cork it has low conductivity to heat, noise and vibration.
It burns without a flame and does not emit toxic gases during combustion. It does not absorb dust and is fire resistant in its natural state.
Highly abrasion resistant
Cork is extremely resistant to abrasion and has a high friction coefficient. Thanks to its honeycomb structure, its resistance to impact or friction is greater than other hard surfaces.
Because cork does not absorb dust, it helps protect against allergies and does not pose a risk to asthma sufferers.