Cork- the thick bark of the cork oak tree (quercus suber)- is a remarkable material. It is tough, elastic, buoyant, and fire resistant and suitable for a wide range of purpose, It has also been used for millennia, the ancient Egyptians sealed their sarcophagi with cork, while the ancient Greeks and romans used it for anything from beehives to sandals.
And the cork oak itself is an extraordinary tree, Its bark grows up to 20 cm in thickens, insulating the tree like a coat wrapped around the trunk and branches and keeping the inside at a constant 20 degree Celsius all year round. Developed most probably as a defense against forest fires, the bark of the cork oak has a particular cellular structure-with about 40 million cells per cubic centimeter that technology has never succeeded in replicating. The cells are filled with air, which is why cork is so buoyant. It also has an elastic that means you can squash it and watch it spring back to its original size and shape when you release the pressure.
Cork oats grow in a number of Mediterranean countries, including Portugal, Spain, Greece and Morocco. They flourish in warm, sunny climates where there is a minimum of 400 millimeters of rain per year, and not more than 600 millimeteres. Like grape vines, the trees thrive in poor soil, putting down deep roots in southern Portugal’s Alentejo region meets all of these requirements, which explains why, by the early 20th century, this region had become the world’s largest producers of cork, and why today it accounts for roughly half of all cork production around the world.
Most cork forests are family-owned. Many of these family businesses and indeed many of the trees themselves are around 200 years old. Cork production is, above all, an exercise in patience. From the planting of a cork sapling to the first harvest from an individual tree. And for top quality cork, it’s necessary to wait a further 15 or 20 years. You even have to wait for the right kind of summer’s day to harvest cork. If the bark is stripped on a day when it’s too cold-or when the air is damp-the tree will be damaged.
Cork harvesting is a very specialized profession. No mechanical means of stripping, so the job is done by teams of highly skilled workers. First they make vertical cuts down the bark using small sharp axes, than lever it away is pieces as large as they can manage. The most skillful cork-strippers prise away a semicircular husk that runs the length of the trunk from just one ground level to the first branches. It is then dried on the ground for about four months, before being taken to factories, where it is boiled to kill any insects that might remain in the cork. Over 60% of the cork that goes on to be made into traditional bottle stopper, with most of the reminder being used is the construction trade.
Corkboard and cork tiles are ideal for thermal and acoustic insulation while granules of cork are used in the manufacture of concrete.
Recent years have seen the end of the virtual monopoly of cork as material for bottle stoppers, due to concerns about the effect it may have on the contents of the bottle. This is caused by a chemical compound called 2,4,6- TCA which forms through the interaction of plants phenols, chlorine and mould. The tiniest concentrations- as little as three or four parts to a trillion-can spoil the taste of the product contained in the bottle. The result has been a gradual yet steady move first towards plastics stoppers and more recently, to aluminum screw caps. These substitutes are cheaper to manufacture and in case of screw caps, more convenient for the user.
The classic cork stopper does have several advantages, however. Firstly, its traditional image is more in keeping with that of the type of high quality goods which it has long been associated. Secondly- very importantly- cork is a sustainable product that can be recycled without difficulty. Moreover, cork forests are a resource which support local biodiversity, and prevent desertification in the regions where they are planted. So, given the current concerns about environmental issues, the future of this ancient material once again looks promising.