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Cork

Cork material is a subset of generic cork tissue, harvested for commercial use primarily from the Cork Oak tree, Quercus suber, with Portugal producing most cork worldwide. Cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle stoppers, especially for wine bottles. Cork stoppers represent about 60% of all cork based production. Cork's low density makes it a suitable material for fishing floats and buoys. Sheets of cork, often the byproduct of more lucrative stopper production, are used to make floor tiles and bulletin boards. The cork industry is generally regarded as environmentally friendly. The sustainability of its production and the easy recycling of cork's products and by-products are two of its most distinctive aspects. Cork demand has increased due to a larger proportion of wine being sealed with cork rather than being sold in bulk. Since a tree's bark can only be harvested once a decade or so, supply is highly inelastic. Top quality corks are quite expensive, so cheaper brands have switched to lower quality cork, synthetic plastic stoppers, screwcaps, or other closures. These also eliminate cork taint. The synthetic stoppers also do not dry out and shrink so the bottles do not have to be on their sides to prevent the wine from oxidizing. However, on the down side, both synthetic stoppers and screwcaps require different winemaking methods to some extent, as sulfur dioxide (SO2) levels need to be different, and there may be different wine faults due to oxidation or reduction. Cork contamination with harmless but foul-smelling trichloroanisole (TCA) is one of the primary causes of cork taint in wine. Cork related trichloroanisole has been reduced by means of new and more reliable production methods, such as changes in the bleaching process. Recently cork has also been used in rocket technology due to its fire resistance. It can also be used as bricks for the outer wall of a house (this was seen at the Portugal Pavilion Expo 2000). Note that the Cork Oak is unrelated to the "cork trees"
(Phellodendron), which though they have corky bark, are not used for cork production.

How many times have you opened a bottle of wine, sniffed the cork, and promptly thrown it out? Just what is that thing made of, and why is it used instead of rubber or screwcaps or something else? Read and learn!    

Cork comes from the cork tree, or Quercus Suber. This is a species of oak that grows in Spain and Portugal. Cork trees are very carefully cared for - the older the tree, the more cork it produces. Some trees grow to be 170 years old.

Cork naturally grows to form 14-sided cells in the bark. Strips are carefully removed (it's in their best interest to keep the tree healthy!) and dried in strips for 6 months. Next the strips are boiled for 90 minutes, then again dry for 3 weeks. Finally, the cork is cut into the shapes you know. Only 40% of this final cut ends up being usable. Cork must be stored carefully until it is used by the winery.

    The whole reason cork is used is to prevent oxygen from getting to, and spoiling, the wine. Cork was known back in Greece and Rome to have this great property and for having that great 'sealing property'. In medieval times they tried to use wood in their sacks and pottery urns. When they developed glass bottles in the 17th century, wood did not work any more as a stopper. Cork was rediscovered and used ever since.    

The first corks were tapered to fit into the bottles more easily. With more modern packing systems, they now have straight sides. Some now have plastic tops as well. Champagne corks actually start out with straight sides, and only develop that "mushroom" shape after being jammed into the bottles. They are not solid cork - to save money, there are disks of cork separated by a "cork mash".
You can tell several things from a cork. Many are marked with the place the cork was made, as well as the winery the wine came from. The narrower and more misshapen the cork, the longer the cork has been in the bottle. Sometimes you will see small crystals around the cork - this is not broken glass, but merely tartrates, a harmless substance sometimes found in wine.

"Real" cork can sometimes develop a mold, and lead to 'corking' of the wine. This sad state makes the wine completely undrinkable. To combat this, a number of wineries are turning to synthetic corks that have the wonderful sealing properties of real cork, but do not harbor molds.

Cork comes from the bark of the cork oak tree which is grown mostly in Europe and northern Africa, with Portugal being a key player. The trees themselves have a typical lifespan common to that of other hardwood species ranging from 150-200 years. After the cork tree reaches its maturity for harvest(apprx.25 years) the bark is removed carefully and sent to an aging location for a period of 3-6 months. Only 50% of the cork bark is removed to allow the tree to protect itself from the elements and flourish. This procedure is then repeated every nine years.

After harvest it is cleaned and boiled. The rough exterior is cut off and the rest is ground up and mixed in a binder. A paste is then added to the granules and the cork is molded into large blocks and baked. During this baking process different colors will be achieved caused by varying temperatures. Most manufacturers offer light, medium and dark varieties but you should always mix several boxes together during installation because of the variation.

After this procedure The blocks are sliced up into 5mm or 8mm thickness and usually 1' square to make the tiles. There is a cheaper version about 1/8" thick with a fine layer of sliced cork called 'veneered cork' but it is not resilient.. Cork sheet is made in a similar process and is used for floating floor planks.

     Cork is used in organbuilding for gasketing material.

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