What Is Cork And How To Turn It Into Fabric And Bags?

Going far back in time to 3000 BC, people like the Greeks, Egyptians, Romans and Chinese already appreciated the versatility and quality of cork. In fact, the ancient Greeks found that when the cork was removed from the cork oak, a new, better sheath quickly formed.

• In those times people already made cork stoppers for wine and olive oil vessels for their sealing quality.
• Sandals were made out of cork because of the naturally shock absorbing quality.
• Buoys and anchor ropes for fishing nets were made of cork due to their floating quality.
• The Romans even used cork to make beehives because of its low heat conduction.

Cork has been the one-size-fits-all closure solution for ages. It's only recently that it faces competition from alternative closures. There are many stories and myths going around about a supposably lack of cork and that the cork oak tree is endangered. And that they slowly are replacing the real cork of wine bottles with plastic corks or with aluminium screw cap instead for that reason. This whole story is a hoax.

The real reason of this cork replacement is that all other options are cheaper and that screw caps are more convenient. But be aware: an aluminium screw cap requires 24 times as many carbon emissions to produce as a natural cork. Moreover, there are enough cork trees today in the sustainable cork forests of Portugal to last for over 100 years. So there’s enough harvestable cork to seal all of the wine bottles produced in the world for the coming century.

Only natural cork and agglomerated cork (natural cork pieces that are bounded by an organic binder) can be recycled (not the waxed cork or granulated cork called DIAM, nor the obvious synthetic plastic cork). When natural cork is recycled it becomes a composite grain, a granulated material. Also waste during the production of cork stopper or the rejected corks are returned to the process and get recycled as well.

There are recycling initiatives all over the world that specialise in recycling the natural wine corks through drop off points located in supermarkets, restaurants and bars. The collected corks are ground up and used to make goods such as footwear, yoga mats, surf gear, flooring and wall tiles and bulletin boards, etc.

NOTE: Both agglomerated and granulated cork can, by using moulds, be shaped in any form. Recycled cork from used cork stoppers cannot be used for new cork stoppers.

Cork is a natural raw impermeable buoyant material grown around the trunk of the cork oak tree, the phellem layer, which is the outermost layer of the tree bark. Cork is actually a conglomeration of dead cells.

Cork is a renewable resource. No tree is cut down to harvest cork, which means the tree keeps on living and the cork after every harvest regrows back.

Cork material, in its natural form, is 100% natural and biodegradable. The lines running through them are called lenticels (small holes and splits in the cork) which are the gas exchange pores allowing air to get through the bark layer to the tree. The cork quality is determined by the number of these lenticels, the fewer the better.

1. Bark: consists of two layers, an outer dead layer (periderm, see 2) and an inner living layer (see 3 and 4).
2. Cork & cork cambium (phellem, phellogen and phelloderm / outer bark): non-functioning primary phloem (dead tissue) that protects the tree.
3. Living functional phloem (secondary phloem / inner bark): transports sugars produced by photosynthesis.
4. Vascular cambium (secondary phloem, and xylem / inner bark): produces new wood which increase the width of the stem.
5. Sapwood (early wood & late secondary wood, active xylem): transports water and minerals.
6. Heartwood (non-functioning primary wood, dead xylem): helps support the tree.
7. Pith

The cork oak tree (in Latin: Quercus Suber) is a tree with a voluminous bark with suberose tissue (the cork). The cork oak is a majestic tree that has been around longer than mankind. Its presence in the world is believed to date back to about thirty million years ago.

Although related to the more common oak trees that are more worldly spread, cork oaks do not have the same typical oak leaf shape. They are oval, smooth and leathery. The cork oak has green foliage all year round, and can reach up to 10 to 15 meters in height when it is a matured tree.

The cork oak tree has a great longevity and an enormous capacity for regeneration. It takes 25 years before it starts to produce cork and lives ± 250 years.

The agroforest areas are native to the western Mediterranean basin, most are in Portugal and Spain. The world's largest cork producer is Portugal, with a share of almost 50%, and around 28,000 people employed in the cork industry. Cork oaks can also grow in other places, but their produce is not always commercially suitable.

• Portugal produces annually 100,000 Tons = 49.6%
• Spain produces annually 61,504 Tons = 30.5%

Due to reforestation programs, the areas of Montados have been increasing in the recent years. In Portugal and Spain over 130 thousand hectares were planted in the last 15 years.

Cork oaks grow in agroforests called Montados in Portugal, or Dehesas in Spain. Both terms mean a multi-purpose agroforestry system with an open tree layer above a grass layer which depends on human practices and management.

The cork oak forests achieved the Forest Stewardship Council (FSC) certification, recognizing that these forests and operations are managed to the highest international social and environmental standards.

These oak forests are large eco-systems, hotspots of biodiversity forming crucial habitats for various threatened animal and plant species and also preventing desertification. Over 200 species of animals like birds, reptile/amphibious, mammals etc. and 135 species of plants can be found in these agroforests.

Harvesting of the bark is a manual ancient process executed by very experienced people called the “descortiçadores”, who do not harm nor kill the tree. Their razor sharp hand-forged iron axe is called “machada” (a broad hewing Viking type of axe) that is about a meter long with a wooden handle shaped into a wedge at the bottom. The axe form shape is like a ginkgo leaf.

First they make a vertical cut along the cork by choosing the deepest crack in the cork bark, this marks until where the cork plank should be removed and what is to remain on the tree. Then they open the bark and put the edge of the axe in the cut and by twisting it, it separates the outer from the inner bark. The bark is then prised of the tree, with the edge of the axe being put between the strip and the inner bark. Thereafter, the axe is twisted between the trunk and the cork strip to be extracted.

Harvesting is only done between the end of May, beginning of June and end of August, when there is water in the tree and when the cells (phellogen) maintain their activity and continue to divide themselves.

The cork expands when the weather is warmer, which also makes harvesting easier. Only under these conditions can the cork be extracted from the tree without any damage.

After the cork is removed, the exposed tissue reveals a dark reddish brown color, and the tree gets marked by using the last number of that year. The cork bark will regrow, regenerate, to become harvested every 9 years. During its lifetime, a cork oak can produce, on average, 15 bark harvests.

The cork quality of a tree changes over the years. The first harvest only happens when a tree is 25 years old and the trunk circumference is 70 cm. This “virgin” tree delivers a very irregular cork structure at start called “desbóia” a virgin cork that is hard and cannot be used for cork stoppers but is suitable for flooring or insulation.

Nine years later, the second harvest produces material with a more regular structure, less hard, but still not suitable for cork stoppers – this is known as ”secondary cork”. It is from the third harvest when the tree is around 43 years old and its following harvests after, that the cork has the best properties and is suitable to use for cork stoppers. This smoothest high end quality cork is called “Amadia”.

By stripping the Cork oak tree from its cork bark the cork oak is able to absorb much higher levels of CO2 than before. A harvested cork trees absorbs 3-5 times more CO2 than non-harvested trees. It is estimated that every year cork oak forests absorb up to 14 million tonnes of CO2.

Once all the cork oak bark has been collected, the slabs are stacked on pallets and exposed to the open air for six months in the rain, wind and sun, which really improves its quality.

In general, the outside seasoned air and natural weather helps the bark to flatten, strengthen, and cure it.

After the seasoned period, the cork bark is transported to factories for further processing. The vast majority of the cork harvest is made into wine bottle stoppers but, increasingly, more and more cork is being sold to construction and fashion industries all over the world. The world’s three biggest cork exporters are Portugal, Spain and France.

Although cork products like cork fabric are also still made primarily in Spain, Portugal, and France, other countries are increasingly making products based on cork.

Sustainable materials such as cork also have disadvantages, of course. Since cork oaks can only grow under certain climatic conditions in the Mediterranean region, transport distances are longer than for the local extraction of wood. This in turn leads to an increased CO2 consumption. However thanks to the light weight quality of cork the impact is less than for heavy weight products.

The cork barks get boiled for at least 24 hours to soften them, clean them, to remove tannic acid and resins and to get them ready for further processing.

The boiling process increases the elasticity and the volume of the material, decreases its density, and functions as a natural fertilizer. After cooling down and drying for a second time, the cork is stabilizing for about two weeks to decrease its humidity to a degree that makes further processing possible.