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Cork (material)

Cork is an impermeable, buoyant material, a prime-subset of bark tissue that is harvested for commercial use primarily from Quercus suber (the Cork Oak), which is endemic to southwest Europe and northwest Africa. Cork is composed of suberin, a hydrophobic substance, and because of its impermeability, buoyancy, elasticity, and fire resistance, it is used in a variety of products, the most common of which is for wine stoppers. Portugal produces approximately 50% of cork harvested annually worldwide, with Corticeira Amorim being the leading company in the industry.[1] Cork was examined microscopically by Robert Hooke, which led to his discovery and naming of the cell.[2]

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 bubble-form structure and natural fire resistance make it suitable for acoustic and thermal insulation in house walls, floors, ceilings and facades. The by-product of more lucrative stopper production, corkboard is gaining popularity as a non-allergenic, easy-to-handle and safe alternative to petrochemical-based insulation products which are flammable and emit highly toxic fumes when burned.

Sheets of cork, also often the by-product of more lucrative stopper production, are used to make bulletin boards as well as floor and wall tiles.

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).

Granules of cork can also be mixed into concrete. The composites made by mixing cork granules and cement have lower thermal conductivity, lower 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).[6]

Use for wine bottle closures
As late as the mid-17th century, French vintners did not use cork stoppers, using oil-soaked rags stuffed into the necks of bottles instead.[7]

Wine corks can be made of either a single piece of cork, or composed of particles, as in champagne corks; corks made of granular particles are called "technical corks".

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.

Because of the cellular structure of cork, it is easily compressed upon insertion into a bottle and will expand to form a tight seal. The interior diameter of the neck of glass bottles tends to be inconsistent, making this ability to seal through variable contraction and expansion an important attribute. However, unavoidable natural flaws, channels, and cracks in the bark make the cork itself highly inconsistent. In a 2005 closure study 45% of corks showed gas leakage during pressure testing both from the sides of the cork as well as through the cork body itself.[8]

Since the mid-1990s, a number of wine brands have switched to alternative wine closures such as synthetic plastic stoppers, screw caps, or other closures. In some countries, screw caps are often seen as a cheap alternative destined only for the low grade wines; however, in Australia, for example, the majority of non-sparkling wine production now uses these caps as a cork alternative. These alternatives to real cork have their own properties, some advantageous and others controversial. For example, while screwtops are generally considered to offer a trichloroanisole (TCA) free seal they reduce the oxygen transfer rate to almost zero, which can lead to reductive qualities in the wine. TCA is one of the primary causes of cork taint in wine. However, in recent years major cork producers (Amorim, Álvaro Coelho & Irmãos, Cork Supply Group, and Oeneo) have developed methods that remove most TCA from natural wine corks. Natural cork stoppers are important because they allow oxygen to interact with wine for proper aging, and are best suited for bold red wines purchased with the intent to age.

The study "Analysis of the life cycle of Cork, Aluminum and Plastic Wine Closures," commissioned by cork manufacturer Amorim and made public in December 2008, concluded that cork is the most environmentally responsible stopper, in a one-year life cycle analysis comparison with the plastic stoppers and aluminum screw caps.[9]


1. J. L. CALHEIROS E MENESES, President, Junta Nacional da Cortiça, Portugal. "The cork industry in Portugal"

2. "Robert Hooke". Retrieved 2010-11-03.

3. Skidmore, Sarah, USA Today (August 26, 2007). "Stopper pulled on cork debate"

4. Henley, Paul, BBC.com (September 18, 2008)"Urging vintners to put a cork in it"

5. PricewaterhouseCoopers/ECOBILAN (October 2008). Analysis of the life cycle of Cork, Aluminium and Plastic Wine Closures.

6. Karade SR. 2003. An Investigation of Cork Cement Composites. PhD Thesis. BCUC. Brunel University, UK.

7. Prlewe, J. Wine From Grape to Glass. New York: Abbeville Press, 1999, p. 110.

8. Gibson, Richard, Scorpex Wine Services (2005). "variability in permeability of corks and closures".

9. Easton, Sally, Decanter.com (December 4, 2008). "Cork is the most sustainable form of closure, study finds".

10. Publico.pt Cork stamp almost sold out (Portuguese)

11. IOL-A Step Beyond Cork stamp debuts in Portugal[dead link]

12. Tomos A35 Clutch Repair


1. Margarida Pi i Contallé. 2006. Laboratory head in Manuel Serra Hongos y micotoxinas en tapones de corcho. Propuesta de límites micológicos aceptables

2. Cork production corkfacts.com

3. Instituto de Promoción del Corcho, Extremadura iprocor.org (Spanish)

4. Analysis of the life cycle of Cork, Aluminium and Plastic Wine Closures

5. Henley, Paul, BBC.com (September 18, 2008). "Urging vintners to put a cork in it".

6. PricewaterhouseCoopers/ECOBILAN (October 2008). Analysis of the life cycle of Cork, Aluminium and Plastic Wine Closures

This article uses material from the Wikipedia article "Cork (material)", which is released under the Creative Commons Attribution-Share-Alike License 3.0.