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The Story of Cork

The Story of Cork





Cork is a wonder of nature. It grows only on one tree the cork oak tree. Cork trees occupy vast areas and are constantly reproducing.

The areas occupied by cork trees are situated west of the Mediterranean basin and on the Atlantic coast. The cork trees needs a lot of light, relatively little rain, a degree of humidity, and thrives in altitudes up to 1,400 meters (above sea-level).

The cork tree has a natural reproduction, by acorns or, more frequently, by producing shoots; however, these processes can be improved with extra care. The systematic plantation of cork oaks, particularly in Portugal, the number one producer with 50% of total world crops, has been a major contribution to the development and improvement of yields. Attempts made in plantations in new countries, for example US, Japan, USSR and South America have not proved viable.

Cork renews itself every 9 or 10 years over approximately 150 years.

Like all trees, the cork oak bears sap wood formed from the bast (or inner bark) and the core. However, what sets it apart from other trees, is its capacity to create a remarkable suberin tissue from its inner bark when it is separated from its protective covering.

The productive layers of the bast (inner bark), are called respectively: the internal productive layer or cambium, which grows towards the wood core of the tree and the external productive layer or phloem, which grows in the direction of the bark and produces cork.

In this way cork is formed at a rate of 1.5 mm per year in the first years, and later 1 mm per year, till a thickness of more than 60 mm is reached. This cork is called virgin cork and does not come away by itself; it is hard, and unsuitable for cork rings. It is used for the manufacture of bonding materials, because, after cork expansion by heat, the resin it contains becomes an excellent agglomerate.

When the trunk of the oak cork tree has reached a circumference of at least 0.80 meters, which corresponds to a virgin cork layer of 30 to 35 mm, the process of unmasking or peeling of the cork may take place. The expression "unmasking the virgin cork" is particularly appropriate since that part of the tree, which is revealed when the virgin cork is removed, is called the mother.

The stripping, when well done, does not harm the trees, because the first layer of reproduction cork merges with the continuously developing virgin layer in the unpeeled part of the tree.

The area know as the 'mother' changes from a rose color to red ochre, then a reddish brown, and the following year to a gray, crust-like formation. From this the reproduction cork originates, at a rate of 1.5 mm to 4 mm per year. It is necessary to wait at least 9 years after stripping the virgin cork, before stripping again so as to get the first useful harvest, that is to say a thickness of around 2 to 5 cm.

The annual formation of the reproduction cork varies according to:
-the nature of soil,
-the climatic conditions,
-the vitality of the tree.

The collection of the cork or the harvest, may be repeated every 9 years, and up to 12 or 15 harvests may be reaped. After this, the tree will no longer be acceptably productive.

In conclusion... Cork trees grow and spread continuously. The cork or the cork tree is constantly renewed. This means that cork, unlike other raw materials, is in two ways a never ending product.

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