Cork material is a prime-subset of generic cork tissue, harvested for commercial use primarily from the Cork Oak tree, Quercus suber, with Portugal producing 50% of cork worldwide. Cork consists mostly of suberin.
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Sources and harvesting
There are about 2,200,000 hectares of cork forest worldwide; 33% in Portugal, and 23% in Spain. Annual production is about 340,000 Tons; 52% from Portugal, 32% from Spain, 6% Italy.
Once the trees are about 25 years old the cork is stripped from the trunks every 9 years. The trees live for about 200 years. The first 2 harvests produce poorer quality cork.
The cork industry is generally regarded as environmentally friendly1. The sustainability of production and the easy recycling of cork products and by-products are two of its most distinctive aspects. However, only two cork companies, Oeneo Bouchage of France, and the Cork Supply Group of Portugal, have conducted and released their complete carbon footprint studies.
Properties and uses
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, as well as handles for fishing rods (as an alternative to neoprene).
Sheets of cork, often the by-product of more lucrative stopper production, are used to make floor tiles and bulletin boards.
Granules of cork can also be mixed into concrete. The composites made by mixing cork granules and cement have low thermal conductivity, low density and good energy absorption. Some of the property ranges of the composites are density (400–1500 kg/m³), compressive strength (1–26 MPa) and flexural strength (0.5–4.0 MPa).2
Use for wine bottle closures
Natural cork closures are used for about 80% of the 20 billion bottles of wine produced each year.
After a decline in use as wine-stoppers due to the increase in the use of cheaper synthetic alternatives, cork wine-stoppers are making a comeback and currently represent approximately 60% of wine-stoppers today.
Corks used as bottle stoppers can sometimes become dry and or shrink due to compression around the mouth of the bottle. This causes them not to form a tight seal. This problem can be easily solved by wetting the cork and then heating it. this causes cells to expand and the cork goes from dry and hard to moisturized and elastic, thus making much more suitable for a bottle stopper.
Cork demand has increased due to more wine being sealed with cork rather than being sold in bulk. Since a tree's bark can only be harvested six to nine years hence, supply is highly inelastic. Top quality corks are expensive, and no matter what the cost, have the risk of containing TCA Cork taint and are susceptible to random oxidation due to their mechanical variability. Many cheaper brands have switched to lower quality cork, synthetic plastic stoppers, screwcaps, or other closures. Because synthetic stoppers are cheaper and do not dry out and shrink, wine bottles with synthetic corks do not have to be stored on their sides to prevent oxidizing. Cork contamination with harmless but foul-smelling trichloroanisole (TCA) is one of the primary causes of cork taint in wine. However, in recent years major cork producers (Amorim, Cork Supply Group and Oeneo) have developed methods that remove TCA from natural wine corks.
As late as the mid 1600s, French vintners did not use cork stoppers, using oil-soaked rags stuffed into the necks of bottles instead.3
Other uses
Cork is used in musical instruments, particularly woodwind instruments, where it is used to fasten together segments of the instrument, making the seams airtight.
Cork can be used as bricks for the outer walls of houses, as in Portugal's pavilion at Expo 2000.
On November 28, 2007, the Portuguese national postal service CTT issued the world's first postage stamp made of cork.45
Cork has been used in rocket technology due to its fire resistancecitation needed.
Miscellaneous
The Cork Oak is unrelated to the "cork trees" (Phellodendron), which have corky bark but are not used for cork production.
Cork was examined microscopically by Robert Hooke and he discovered and named the cell.
See also
- Alternative wine closures
- APCOR, Portuguese Cork Association
- Cork cambium
- Cork borer
- Corkscrew
- Cork Boat (vessel)
Sources
- Cork production corkfacts.com
- Instituto de Promoción del Corcho, Extremadura iprocor.org (Spanish)
- Footnotes
- ^ "Stopper pulled on cork debate", USA Today, August 26, 2007
- ^ Karade SR. 2003. An Investigation of Cork Cement Composites. PhD Thesis. BCUC. Brunel University, UK.
- ^ Prlewe, J. Wine From Grape to Glass. New York: Abbeville Press, 1999, p. 110.
- ^ Publico.pt Cork stamp almost sold out (Portuguese)
- ^ IOL-A Step Beyond Cork stamp debuts in Portugal