Cork (material)
Overview
 
Cork is an impermeable, buoyant
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 material, a prime-subset of bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...

 tissue that is harvested for commercial use primarily from Quercus suber (the Cork Oak), which is endemic to southwest Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and northwest Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. Cork is composed of suberin
Suberin
Suberin is a waxy substance found in higher plants. Suberin is a main constituent of cork, and is named after the Cork Oak, Quercus suber.-Anatomy and physiology:...

, 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.
Encyclopedia
Cork is an impermeable, buoyant
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 material, a prime-subset of bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...

 tissue that is harvested for commercial use primarily from Quercus suber (the Cork Oak), which is endemic to southwest Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and northwest Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. Cork is composed of suberin
Suberin
Suberin is a waxy substance found in higher plants. Suberin is a main constituent of cork, and is named after the Cork Oak, Quercus suber.-Anatomy and physiology:...

, 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
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

 produces approximately 50% of cork harvested annually worldwide, with Corticeira Amorim
Corticeira Amorim
Corticeira Amorim S.G.P.S., S.A., is a Portuguese subholding company belonging to the Amorim Group and claims to be the world leader in the cork industry for over 130 years, with operations in hundreds of countries all over the world. Corticeira Amorim S.G.P.S., S.A...

 being the leading company in the industry. Cork was examined microscopically by Robert Hooke
Robert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...

, which led to his discovery and naming of the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

.

Sources

There are about 2,200,000 hectares of cork forest worldwide; 32.4% in Portugal, and 22.2% in Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

.
Annual production is about 300,000 tons; 52.5% from Portugal, 29.5% from Spain, 5.5% Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

.

Once the trees are about 25 years old the cork is stripped from the trunks every ten years. The trees live for about 200 years. The first two harvests produce poorer quality cork.

The cork industry is generally regarded as environmentally friendly. The sustainability
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...

 of production and the easy recycling
Recycling
Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...

 of cork products and by-products are two of its most distinctive aspects. Cork Oak
Cork Oak
Quercus suber, commonly called the Cork Oak, is a medium-sized, evergreen oak tree in the section Quercus sect. Cerris. It is the primary source of cork for wine bottle stoppers and other uses, such as cork flooring. It is native to southwest Europe and northwest Africa.It grows to up to 20 m,...

 forests also prevent desertification
Desertification
Desertification is the degradation of land in drylands. Caused by a variety of factors, such as climate change and human activities, desertification is one of the most significant global environmental problems.-Definitions:...

 and are the home of various endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

.

Carbon footprint
Carbon footprint
A carbon footprint has historically been defined as "the total set of greenhouse gas emissions caused by an organization, event, product or person.". However, calculating a carbon footprint which conforms to this definition is often impracticable due to the large amount of data required, which is...

 studies committed by Corticeira Amorim
Corticeira Amorim
Corticeira Amorim S.G.P.S., S.A., is a Portuguese subholding company belonging to the Amorim Group and claims to be the world leader in the cork industry for over 130 years, with operations in hundreds of countries all over the world. Corticeira Amorim S.G.P.S., S.A...

, Oeneo Bouchage of France and the Cork Supply Group of Portugal concluded that cork is the most environmentally friendly wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 stopper
Stopper (plug)
A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...

 in comparison to other alternatives. The Corticeira Amorim
Corticeira Amorim
Corticeira Amorim S.G.P.S., S.A., is a Portuguese subholding company belonging to the Amorim Group and claims to be the world leader in the cork industry for over 130 years, with operations in hundreds of countries all over the world. Corticeira Amorim S.G.P.S., S.A...

’s study, in particular ("Analysis of the life cycle of Cork, Aluminum and Plastic Wine Closures"), was developed by PricewaterhouseCoopers
PricewaterhouseCoopers
PricewaterhouseCoopers is a global professional services firm headquartered in London, United Kingdom. It is the world's largest professional services firm measured by revenues and one of the "Big Four" accountancy firms....

, according to ISO 14040. Results concluded that, concerning the emission of greenhouse gases, each plastic stopper released 10 times more CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, whilst an aluminium stopper releases 26 times more CO2 than does a cork stopper.

Cork Oak forests comprise the majority of habitat for the Iberian lynx
Iberian Lynx
The Iberian lynx, Lynx pardinus, is a critically endangered species native to the Iberian Peninsula in Southern Europe. It is one of the most endangered cat species in the world. According to the conservation group SOS Lynx, if this species died out, it would be one of the few feline extinctions...

, one of the most endangered cat species in the world. Its decline has been a function of a loss of habitat due to development of housing as well as the introduction of a virus to control the rabbit population which was the lynx's primary prey.

The Cork Oak is unrelated to the "cork trees" (Phellodendron
Phellodendron
Phellodendron or Cork-tree, is a genus of deciduous trees in the family Rutaceae, native to east and northeast Asia. It has leathery, pinnate leaves and yellow, clumped flowers. The name refers to the thick and corky bark of some species in the genus.-Cultivation and uses:As an ornamental plant,...

), which have corky bark but are not used for cork production.

Harvesting

Cork is only extracted from early May to late August, when the cork can be separated from the tree without causing permanent damage. When the tree reaches 25-30 years of age and about 24in (60cm) in circumference, the cork can be removed for the first time. However, this first harvest almost always produces poor quality or "male" cork. Subsequent extractions usually occur at intervals of 10 years, thought it can take up to 13 for the cork to reach an acceptable size. If the product is of high quality it is known as "gentle" cork, and, ideally, is used to make stoppers for wine and champagne bottles.

The workers who specialize in removing the cork are known as extractors. Extractors use a very sharp axe to make two types of cuts on the tree: one horizontal cut around the plant, called a crown or necklace, at a height of about 2-3 times the circumference of the tree, and several vertical cuts called rulers or openings. This is the most delicate phase of the work because, even though cutting the cork requires quite a bit of force, the extractor cannot damage the underlying phellogen or the tree will die.

To free the cork from the tree the extractor pushes the handle of the axe into the rulers. A good extractor needs to use a firm but precise touch in order to free a large amount of cork without damaging the product or tree.The cork harvest

These freed portions of the cork are called planks. The planks usually have to be carried off by hand since cork forests are rarely accessible for vehicles. Finally, the cork is stacked where it can be loaded onto a truck and shipped to a processor.

Properties and uses

Cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle
Bottle
A bottle is a rigid container with a neck that is narrower than the body and a "mouth". By contrast, a jar has a relatively large mouth or opening. Bottles are often made of glass, clay, plastic, aluminum or other impervious materials, and typically used to store liquids such as water, milk, soft...

 stoppers
Stopper (plug)
A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...

, especially for wine bottle
Wine bottle
A wine bottle is a bottle used for holding wine, generally made of glass. Some wines are fermented in the bottle, others are bottled only after fermentation. They come in a large variety of sizes, several named for Biblical kings and other figures. The standard bottle contains 750 ml,...

s. 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
Flooring
Flooring is the general term for a permanent covering of a floor, or for the work of installing such a floor covering. Floor covering is a term to generically describe any finish material applied over a floor structure to provide a walking surface...

.

Cork's low density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 makes it a suitable material for fishing
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....

 floats
Float (fishing)
A float, also called a bobber, is a device used in angling that serves two main purposes: it can suspend the bait at a predetermined depth, and it can serve as a bite indicator. They are often used in conjunction with a fishing sinker. Fishing with a float is called float fishing.Floats come in...

 and buoys, as well as handles for fishing rod
Fishing rod
A fishing rod or a fishing pole is a tool used to catch fish, usually in conjunction with the pastime of angling, and can also be used in competition casting. . A length of fishing line is attached to a long, flexible rod or pole: one end terminates in a hook for catching the fish...

s (as an alternative to neoprene
Neoprene
Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...

).

Granules of cork can also be mixed into concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

. 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).

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.

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
Closure (wine bottle)
Closure is a term used in the wine industry to refer to a stopper, the object used to seal a bottle and avoid harmful contact between the wine and oxygen.They include:* Traditional natural cork closures ;...

 are used for about 80% of the 20 billion bottles of wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 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.

Since the mid-1990s, a number of wine brands have switched to alternative wine closures
Alternative wine closures
Alternative wine closures are substitute closures used in the wine industry for sealing wine bottles in place of traditional cork closures. The emergence of these alternatives has grown in response to quality control efforts by winemakers to protect against "cork taint" caused by the presence of...

 such as synthetic plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 stoppers, screw caps
Screw cap (wine)
A screw cap is a metal cap that screws onto threads on the neck of a bottle, generally with a metal skirt down the neck to resemble the traditional wine capsule . A layer of plastic , cork, rubber, or other soft material is used as wad to make a seal with the mouth of the bottle...

, 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
Cork taint
Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening...

 (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
Cork taint
Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening...

 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
Amorim
Amorim is a Portuguese surname. A habitational name from any of the various places named Amorim, originally Amorini, from the name of the estate owner.It may refer to:- People :*Ana Amorim, Brazilian handball player...

 and made public in December 2008, concluded that cork is the most environmentally responsible stopper, in a one-year life cycle analysis
Life cycle assessment
A life-cycle assessment is a technique to assess environmental impacts associated with all the stages of a product's life from-cradle-to-grave A life-cycle assessment (LCA, also known as life-cycle analysis, ecobalance, and cradle-to-grave analysis) is a technique to assess environmental impacts...

 comparison with the plastic stoppers and aluminum screw caps.

Other uses

Cork is used in musical instruments, particularly woodwind instrument
Woodwind instrument
A woodwind instrument is a musical instrument which produces sound when the player blows air against a sharp edge or through a reed, causing the air within its resonator to vibrate...

s, where it is used to fasten together segments of the instrument, making the seams airtight. Conducting baton handles are also often made out of cork.

It is also used in shoes, especially those using Goodyear Welt Construction.

Cork can be used as brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

s for the outer walls of houses, as in Portugal's pavilion at Expo 2000
Expo 2000
Expo 2000 was a World's Fair held in Hanover, Germany from Thursday, June 1 to Tuesday, October 31, 2000. It was located on the Hanover fairground , which is famous for hosting CeBIT...

.

On November 28, 2007, the Portuguese national postal service CTT issued the world's first postage stamp
Postage stamp
A postage stamp is a small piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage. Typically, stamps are made from special paper, with a national designation and denomination on the face, and a gum adhesive on the reverse side...

 made of cork.

Cork is used as the core of both baseballs and cricket ball
Cricket ball
A cricket ball is a hard, solid leather ball used to play cricket. Constructed of cork and leather, a cricket ball is heavily regulated by cricket law at first class level...

s. A corked bat
Corked bat
In baseball, a corked bat is a specially modified baseball bat that has been filled with cork or other lighter, less dense substances to make the bat lighter without losing much power. A lighter bat gives a hitter a quicker swing and may improve the hitter's timing...

 is made by replacing the interior of a baseball bat
Baseball bat
A baseball bat is a smooth wooden or metal club used in the game of baseball to hit the ball after the ball is thrown by the pitcher. It is no more than 2.75 inches in diameter at the thickest part and no more than 42 inches in length. It typically weighs no more than 33 ounces , but it...

 with cork—a practice known as "corking". It was historically a method of cheating at baseball
Baseball
Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

; the efficacy of the practice is now discredited.

Cork is often used, in various forms, in spacecraft heat shields.

Cork is also used inside footwear to improve climate control and comfort.

Corks are also hung from hats to keep insects away. See cork hat
Cork hat
A cork hat is a type of headgear with cork strung from the brim, to ward off insects.Traditionally worn by jackaroos and swagmen in the blow-fly infested Australian outback, the cork hat has become part of the stereotypical representation of the Australian ocker. The shape and material of cork hats...

.

Cork has been used as a core material in sandwich composite
Sandwich structured composite
A sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff skins to a lightweight but thick core...

 construction.

Cork can be used as the friction lining material of an automatic transmission
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

 clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...

, as designed in certain mopeds.

See also

  • APCOR
    APCOR
    Associação Portuguesa da Cortiça is the Portuguese Cork Association, a consortium of cork growers and manufacturers. It was founded in 1956 and is based in the town of Santa Maria de Lamas in northern Portugal...

    , Portuguese Cork Association
  • Bung
    Bung
    A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...

  • Cork Boat (vessel)
    Cork Boat (vessel)
    Cork Boat is a vessel designed and built by American speechwriter John Pollack and his partner Garth Goldstein. The ship, composed of exactly 165,321 wine corks, took over two years to complete. Over 100 volunteers contributed to the project, and Pollack received numerous donations of materials for...

  • Cork borer
    Cork borer
    A cork borer, often used in a chemistry laboratory, is a metal tool for cutting a hole in a cork or rubber stopper to insert glass tubing. Cork borers usually come in a set of nested sizes along with a solid pin for pushing the removed cork out of the borer...

  • Corkscrew

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK