The Academy of Wine

Most people do not realize that natural cork wine stoppers come from the bark of the cork oak tree, Quercus suber. It is an evergreen tree which is grown almost exclusively in the western Mediterranean and Iberian Peninsula. Cork oak forests can be found in Portugal, Spain, Italy, Morocco, Algeria, Tunisia and France. Portugal’s cork forests are the most productive and account for 30% of the existing trees which produce 50% of the world’s cork harvest.

This tree’s bark is unique throughout the plant kingdom. The bark can be stripped off without harming or killing the tree, with new bark growing to replace it. Every cork tree is a source of new raw material and has a lifespan of approximately 150 years. The bark is composed of dead cells with an amazing honeycomb-like structure. These cells each have 14 sides but are not uniform in shape and are composed of mostly empty space. The density of cork is one-fourth that of water, which makes it very buoyant. With 625 million empty cells per cubic inch, cork is like many layers of microscopic bubble wrap, making it an extremely efficient cushioning material. Because it has a large amount of dead-air, it is a great insulator for both temperature and noise. Cutting the surface of the cork turns many of the cells into tiny suction cups, which creates an efficient non-slip surface. It is quite flexible and resilient too; testing has shown that after being crushed under a pressure of 14,000 lbs. per square inch, cork will regain 90% of its original size in 24 hours. Cork does not absorb dust or moisture, and resists both rot and insects. Cork is fire-retardant. Flames will only char the surface and no toxic fumes are created. Very impressive!

The cork oak tree must be 25 years old before the bark can first be harvested. The first (Virgin) and second (Secondary) harvests of bark cannot be used to make wine corks, but are used to make other products. By law, the bark can be harvested no less than every nine years; making the tree 43 years old before the third harvest when the bark will be smooth and regular enough for making wine corks. Each cork tree will be harvested about 15-18 times during its lifetime.

We do not know when cork was first used, but cork cylindrical stoppers have been found in Egyptian tombs dating back thousands of years. The Ancient Greeks used cork for seals too, but also used it to make fishing net floats and sandals. The Romans used cork in a variety of ways, including life jackets for fisherman. For hundreds of years cottages in the Mediterranean have been built with cork roofs and floors to keep out summer heat and winter cold, and also to provide a soft walking surface. Today, cork is used to make many products including floors, shoe insoles, roofing panels, gaskets, safety helmet liners, bottle stoppers, dartboards, bulletin boards, fishing rod handles, place mats, coasters, and cores for various types of balls. Cork is even used in the nose cone of the NASA Space Shuttle! No general substitute has been developed for cork that can be used in such diverse applications.

Sources:
Cork Oak Tree: www.finishingstore.com
Map: www.panda.org
Cells: instruct1:cit.cornell.edu