Natural cork and wine have been a powerful combination for centuries. Today cork is still the wine closure of choice for U.S. consumers according to recent surveys. It has proven beneficial effects on aging wine and can protect a fine wine for more than 25 years. APCOR, the consortium of Portuguese cork producers, has spent literally millions of dollars to ensure cork remains the number one seal for wines. Production practices, techniques and rigorous quality control procedures have been developed this past decade to deliver the most widely accepted stopper for wine.

But don't take our word for it. Let's take a closer look at cork. Then take our cork certification course once you've read our site and become a qualified cork master.


Where does cork come from and where does it go?

Cork comes from the bark of the cork oak tree (quercus suber L) found mostly in the Mediterranean Basin. Trees are never cut down to make cork. It is harvested from trees that can produce up to 20 harvests over the course of their lifetime. The average lifespan of a tree varies between 170 and 200 years. Portugal is the source for over half of the world’s supply of cork, followed by Spain, Algeria and Italy. Remarkably, while only accounting for a small portion of cork production, the manufacturing of cork closures constitutes 70% of the industry’s income.

The world’s supply of cork is not running out – there are over 963,300 acres of cork trees still not in commercial use, which will be available to provide high quality natural cork for generations to come.

Cork is used around the world in many functions. In 2004, France was the top importer of Portuguese cork, importing 21.8%. After France, the USA imports 16.4%, Spain imports 12.8%, and Germany imports 10.3% of the cork produced in Portugal.

Did you know?

Following the invention of the optical microscope in the 1660s, the British scientist Robert Hooke was the first to observe the structure of cork, for which he coined the term “cell”.

A cork cell is a minute, straight-sided pentagonal or hexagonal prism. About 80 per cent (in volume) of cork is gas enclosed in the cells. Suberose sacs make the cork cell membrane impermeable and the cell airtight. There are about 40 million cells per cubic centimetres of cork.

Suberin, a mixture of fatty acids and heavy organic alcohols, is the basic substance of cork. Impermeable to gas or liquid, it is also fire and insect resistant and unaffected by water.

The average chemical composition of cork is:

  • Suberin (45%) - the main component of the cell walls; responsible for the resilience of the cork
  • Lignin (27%) - the binding compound
  • Polysaccharides (12%) - components of the cell walls which help define the texture of the cork
  • Tannins (6%) - polyphenolic compounds responsible for color
  • Ceroids (5%) - hydrophobic compounds that ensure the imperviousness of cork
  • Mineral water, glycerine, and others make up the remaining 4%.


For over 3,000 years, cork has been used to seal bottles. Egyptian tombs dating back thousands of years were found to contain amphorae with cork stoppers. In China around 3,000 B.C. it was used as a fishing apparatus. Ancient Greeks used it as a stopper for olive oil and wine.

But it was French Benedictine monk Dom Perignon who first used it commercially as a stopper for the sparkling wine of his Hautvilliers monastery in 1680. Since the 1700s, natural cork has been the leading closure for fine wines from every part of the world.

Cork stoppers first arrived in Portugal around 1700 and were first used in the port industry. By 1797, the Portuguese were exporting over 100,000 cork stoppers a year.

Today over 15 billion natural cork stoppers are produced every year.


How is cork harvested?

The harvesting of cork consists of stripping the outer bark of cork oaks. The best time for bark stripping is at the most active phase of the cork oak's annual growth: from May to August.

The first harvest produces cork of a very irregular structure. This is called “virgin cork”.

Nine years later the second harvest brings “reproduction cork” – a material with a more regular structure, less hard, but still not suitable for cork stoppers. Reproduction cork is usually granulated for use in products such as flooring.

It is from the third and subsequent harvests that the cork with the best properties is obtained - the “amadia cork” - and from this time, the tree will provide good quality cork for about 150 years.

The stripped area, known as the “mother,” changes from a rose color to red ochre, then a reddish brown, and the following year to a grey, crust-like formation. Loggers use a special axe for the harvest. The blade is used to make the incision while the end of the handle is shaped to detach the cork.

How is the harvest regulated?
To keep the trees in good health, government laws regulate the harvesting of cork oaks. In Portugal, trees are harvested in cycles of not less than nine years. Calendar years are painted on the bark to monitor when a tree was last stripped.

How is cork stripped from a tree?
The delicate operation of stripping cork has been performed in the same way for decades. Today, cork stripping with a special axe continues to be the quickest, cleanest and most tree friendly method available.

The stripping process consists of five steps:

        1. Opening
        2. Separating
        3. Dividing
        4. Extracting
        5. Removing

What happens after harvest?

After harvest, the cork planks must stabilize. They are sorted according to their future use as natural cork stoppers, discs, or agglomerated cork products, depending on their quality.

The selected planks are then stacked in piles to be exposed to sun, wind and rain for six months or more. During this seasoning period, the elements purge most of the sap from the cork, the polyphenols are oxidized and the cork texture stabilizes.

After stabilization, the cork planks are boiled in clean water for at least one hour. All cork must be boiled before it is worked to make it more pliable, and to fully expand the lenticels.

The cork cells are collapsed and wrinkled before boiling, but after boiling, the gas in the cells expands and creates a very tight, more uniform cell structure. This hot water process makes the cork increase its volume by about 20 per cent, and become flatter and smoother.

The boiling operation - a standard procedure defined by the International Code of Cork Stopper Manufacturing – extracts polyphenols and also ensures that microflora is significantly reduced. Once the boiling is finished, the cork planks are dried and left to rest in warehouses with controlled humidity and temperature for three weeks. Cutters then trim the edges to make the planks rectangular.

The trimmed cork planks are sorted into various thicknesses and qualities, depending on a number of criteria, including porosity.


After the three-week resting period in the warehouse, the trimmed planks are sliced into strips and cork stoppers are punched out. After punching, the ends of each raw cork stopper are cut to size and polished. Suitable leftover cork pieces are processed into agglomerated corks. Agglomerated cork stoppers – made from compressed cork granules – receive the same care and attention to detail as one-piece corks. Unused cork and even cork dust is processed into other cork products such as insulation and construction materials. Nothing from the cork tree is wasted.

The cork stoppers are then scanned to eliminate imperfections detrimental to bottling. The grading procedure assigns each cork stopper a visual level.

This inspection is done with automated optical scanners programmed to select corks on the basis of pattern recognition. Another procedure is to use highly skilled personnel who visually inspect each cork to determine its visual grade.

Treating the stoppers

The selected cork stoppers then undergo the washing and disinfection process. The most common method is washing the cork stoppers in a watery solution of hydrogen peroxide. Besides washing, the cork stoppers also go through new, additional treatment methods such as using microwaves or steam treatments to disinfect them . The next stage is drying the cork stoppers in special ovens. When the moisture levels are lowered and stabilized, stopper performance is maximized and microbial contamination is minimized.

These methods allow for the stabilization of cork without any change or damage to the cell structure, providing yet another barrier to microbial contamination.

After the final selection, the cork stoppers may be printed according to clients' specifications via roller marking, ink marking or traditional branding.

After branding, they are given a final coating of paraffin or silicone to make them easier to insert and extract from the bottles, while at the same time improving their sealing capacity.

Finally, corks are automatically counted, sanitized with sulphur dioxide gas and sealed in gas-barrier bags.


The expression “the cellar makes the wine” is as old as it is true.

The temperature, humidity and hygiene of the cellar all contribute towards the final quality of the wine. The cellar must obey the following criteria:

Room temperature between 15º C (59F) and 20º C (68F), without great thermal variation, during the day and throughout the year.

Humidity level between 40% and 70%.

The cellar must be free of insects and rodents. This does not include spiders, as they are excellent insect predators.

The cellars must not have chemically treated wood.

The cellars must be free of all odors, especially moldy/musty smells.

Chemical products, such as paint or cleaning products, must not be kept in the cellar.

During the maturation of wine, bottles must be stored horizontally. However, wine stored in cases for transportation can be stored vertically provided the storage is only for a relatively short period of time. Under these circumstances, wine has sufficient volatility to keep the bottom end of the cork moist, retaining the cork’s excellent elastic property and an airtight seal.

Properly storing wine with natural corks allows the wines to develop in very unique and pleasant ways. For long storage wines such as Bordeaux and Vintage Port, natural cork can protect and age the wine for up to 25 years.


The bottle should be opened carefully and calmly. First, the capsule that protects the bottleneck must be removed, approximately one centimeter below the top rim of the bottle. After that, especially if the bottle is old, the bottleneck and the top of the cork stopper must be wiped with a clean cloth. The point of the corkscrew is then placed in the center of the cork closure, taking care to insert the spiral of the corkscrew deeply, but not so far that it perforates the bottom of the cork. This operation is not possible with every design of corkscrew, especially some that are not hand operated. If the spiral is not inserted deep enough, the cork is not extracted and the screw can pull through the middle of the cork. If particles of cork do fall into the wine because the spiral of the corkscrew has been inserted too far, there is no serious problem and one should remember these small particles are organically harmless, even if consumed.

One of the main parts of a corkscrew is its spiral. This has to be at least 7 cm in length, to be able to deal with longer corks, and should have a sharp point. In terms of material, the spiral must be a single piece, completely smooth and without sharp edges. The spirals with a PTFE (Teflon™) surface or similar material are recommended as they pierce the cork with ease, without damaging its internal structure.

Depending on the age of the bottle, the cork will be in different stages of evolution. In a new wine, there will be a very robust cork closure, but in more mature wines, the cork closure will have softened. In very old wines, generally with a bottle age of more than 35 years, weaker corks will be found due to their already fragile internal structure. These corks require great care as they often break during extraction.

In the case of sparkling wine, the bottle must be opened with care and without agitation. After the muselet (wire cage) is removed, the cork stopper must be held firmly. Thereafter, the bottle, and not the cork, must be turned, in order to prevent an exaggerated twist of the cork stopper. On removal, the cork will emit that unique “pop,” a reason for joy and enrichment of our senses – something only natural cork can do.


In recent years cork has come under pressure from other wine closures. Market studies in the United States show that consumers prefer cork closures in their wines and it is an important factor when choosing wine.

A 2006 survey of the U.S. wine trade found nine out of ten consumers – a stunning 94% – think that non-cork closures sometimes or often cheapen a bottle of wine.

A 2005 closure survey by the Wine Spectator showed 81 percent of those questioned in an Internet survey preferred cork closures compared to 18 percent who preferred screw caps.

In 2004, Wine Intelligence, a leading international wine industry consultancy, conducted a major survey of American consumer attitudes to two types of seals: cork stoppers and aluminum capsules (screw caps). Two-thirds of the respondents preferred cork stoppers, 52 percent rejected aluminum capsules, and only one percent said they did not like to drink wine sealed with a cork.

A 2002 study by Moulton Hall to monitor consumer attitudes toward natural cork stoppers and other wine bottle closures, found 76% of the consumers preferred cork. (National percentages were the United States 80%, United Kingdom 78%, and Australia 71%.)

The Australian Wine Research Institute carried out a comparative test over 24 months, which determined that natural cork on the whole was the best product to use for aging wines.