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CORKART
About CORKART Flooring  |  Colors & Patterns  |  Chemical Composition  |  Harvesting Cork

HARVESTING CORK - THE PROCESS

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 or June to August.

Cork is harvested in steady cycles that promote healthy growth of the tree over its life span of 150 to 200 years. Each cork oak provides an average of 16 bark strippings.

The first stripping of the cork bark takes place once the tree trunk reaches a circumference of 70 centimeters and stands 120 centimeters tall. However, the cork will only be fit for cork stoppers from the third harvest onwards. So it often takes over 30 years before wine-quality cork can be harvested.
  • 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 stripping, when done by professional loggers, does not harm the tree, because the first layer of reproduction cork merges with the continuously developing virgin layer in the unstripped part of the tree.

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 gray, 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.


© 2002 by APCOR
The harvesting of cork consists of stripping the outer bark of cork oaks.



© 2002 by APCOR
The stripping of cork oaks is done by professional loggers.
Harvesting regulations

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.

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 and cleanest method available.

The stripping process consists of five steps:
  1. Opening
  2. Separating
  3. Dividing
  4. Extracting
  5. Removing
The first operation is opening, where the cork is slashed vertically, choosing the deepest crack in the cork bark. At the same time, the edge of the axe is twisted so as to separate the outer from the inner bark. At this stage it is possible to gauge the degree of difficulty of extraction from the 'feel' of the axe. When the edge of the axe is applied to the strip, a hollow sound of tearing is heard if the cork is going to come off easily. If it is going to be difficult, the axe gives off a short, firm, dry sound.

The plank is then prised off the tree, by inserting the edge of the axe between the strip and the inner bark. The axe is twisted between the trunk and the cork in order to peel off the cork in large panels from the main sections of the trunk.

After a horizontal cut, a dividing line is drawn between the cork plank to be removed and what is to remain on the tree. The plank is then removed from the tree with care so that it does not split. The larger the planks extracted, the greater their commercial value. The removal of entire planks depends on the skill of the workers. After the first plank has been stripped, the operation is repeated over the whole trunk.

After being harvested, 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 period, the elements purge most of the sap from the cork, the polyphenols are oxidized and the cork texture stabilizes.


Boiling cork planks.
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 Practice - also ensures that microflora is significantly reduced. But many manufacturers are using complementary procedures to achieve significant improvements. Some have introduced computer controlled boiling, processed in a closed environment. The cork industry is striving for even better cleaning methods.

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.


© 2002 by APCOR
Automated cork stopper drilling machine. (notice the cork waste produced in the cork stopper production – We will use this type of waste to produce cork floor)
The trimmed cork planks are sorted into various thickness and qualities, depending on the porosity and certain structural defects that the cork may have.
After the three-week resting period in the warehouse, the trimmed planks are sliced into strips and cork stoppers are punched out.

Regular cork strips are ideal for automated punching; less regular strips may be processed by manual punching.

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 solid 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.
Cork stoppers are biodegradable and recyclable. Many local cork recycling initiatives help to conserve this natural resource. Although the recycled cork is never used again for wine stoppers, it has many other uses - such as for the manufacture of memo boards, place mats, coasters, floor tiles and gaskets.

Curiosity: Our Company, Corkart, is based in a region called Alentejo.

In the book “Guinness World Records” we can find a reference to the largest cork tree in the world. The tree exists in Alentejo and produces one thousand kilograms of cork each time the tree is harvested. That amount of cork is sufficient to bottle one hundred thousand bottles. With more than 212 years old the tree produces cork each nine years since 1820. The next harvest will be in 2010.


CORK STOPPERS INDUSTRY

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

The selected cork stoppers then undergo the washing and disinfection’s process. The most common method is washing the cork stoppers in a watery solution of hydrogen peroxide. New methods use microwaves or ozone to disinfect the corks.

The next stage is drying the cork stoppers in special stoves. When the moisture levels are lowered and stabilized, stopper performance is maximized and microbial contamination is minimized.

These methods allow for the elimination of internal moisture in the 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.

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