Quite simply put, cork is the bark of a tree. This bark is thicker and more resilient than the bark of other trees, which is why it is such a good product for commercial applications. Cork has many uses, and as such is a very adaptable product.

Where does the cork tree originate?

Cork is the outer layer of the tree bark. This layer is called the phellem, and it is the dead layer of cells of the bark. Cork itself actually comes from the tree, cork oak, which originates in southwestern Europe and northwestern Africa. The countries of origin specially are France, Portugal, Spain, Morocco, Italy, Algeria, and Tunisia.

It is estimated that there is 2.7 million hectares of cork oaks worldwide. The worldwide total production of cork is approximately 340,000 tons each year. In the order of production quantities of cork for each country they are 49.6% in Portugal, 30.5% in Spain, 5.8% in Morocco, 4.9% in Algeria, 3.5% in Tunisia, 3.1% in Italy, and 2.6% in France. (source)

The cork oak itself is an evergreen tree. This aspect makes it unique, since other trees of similar species are deciduous. Evergreen simply means that the tree doesn’t lose it’s leaves during the winter months. The tree also has the special ability to have the bark peeled off and it will regrow that outer layer over time. This allows for the cork to be harvested without killing the tree. (source)

Cork oaks tend to grow alongside many other tree species such as other types of oaks, pines and olive trees. The cork oak can grow to be around sixty-five feet tall. The tree has thick, porous, dark grey bark. The tree also commonly has low, twisted branches.

Quercus suber is the scientific name of the cork oak. Cork derives it’s name from Robert Hooke, who was the first scientist to study the bark under the microscope in 1665. He was the scientist who named the cell and published his book titled, Micrographia. (source)

How is cork harvested?

Once the cork tree is between fifteen to twenty years old, it is safe to harvest the bark. The cork can only be harvested between the months of May and August so as not to damage the tree. This timeframe is the dormant months for the tree.

Harvesting is done by making two types of cuts on the surface of the tree with an axe, one horizontal cut around the tree and then several vertical cuts to aid in peeling the bark away. The worker, known as an extractor, will strip the bark off by hand so as to prevent permanent damage to the tree.

The first harvest generally produces poor quality cork. It is termed virgin cork and can be used for flooring and shoes. High quality cork is termed gentle cork and is used as stoppers in wine bottles.

This process can be done twelve to thirteen times over the course of the trees approximately 150 year lifespan. The tree is harvested every nine to ten years after each subsequent harvest to ensure that the bark has regrown sufficiently.

The harvested cork, known as planks, is then taken to a factory where it can be dried for six months in the open air. This is referred to as the weathering process and improves the quality of the cork.

How is cork processed?

The planks of cork are stacked and elevated off the ground in such a way as to ensure thorough drying of each piece. After the six month resting period has elapsed, the planks can be sorted and graded for their final use. The high quality cork is set aside for further processing into stoppers. While the poor quality cork is ground and used to make other products in other industries.

The high quality planks are boiled in filtered tanks to remove any debris and to ensure that the proper moisture level is obtained for further processing. The boiling causes the cork cells to expand by approximately twenty percent, which makes the planks easier to handle. The planks are stacked and will be allowed to dry before being graded further. If any of the planks are found to be defective, they will be ground and used in other products. Only the high quality cork will be used to make the stoppers.

The planks will then be cut into strips. These strips are either punched or molded with a machine to ensure that the stopper is consistent in size and shape. The stoppers are processed in accordance with the guidelines published by the Food and Drug Administration (FDA).

What are the commercial applications of cork?

Cork is a natural product and as such is very environmentally friendly, since it is also a renewable resource. Cork has many industrial and commercial uses and is being considered for many new product lines.

Cork is currently used in insulation, since it is a natural fire retardant that has thermal and acoustical properties. Cork is also used in shoes, musical instruments, wallets, baseball cores, ink jet printers, watches, gardening, and glass blowing just to name a few items. It is more commonly seen being used for bulletin boards and flooring as well as stoppers.

New studies have shown that cork is a very versatile and adaptable product that the marketplace is just starting to see the possibilities of utilizing. For example, within the construction industry, cork is better as a core sandwich material, since it has more residual strength than traditional composite materials.

Cork has also been shown to absorb oil and solvents. This can help in controlling oil spills.

What is the longevity of cork?

Cork is a natural antimicrobial, and is resistant to moisture and fire, but still allows for air exchange. About half of cork is made up of trapped air pockets. This is what makes cork so adaptable.

It also is non-toxic and does not give off any volatile compounds. High quality cork can last up to fifty years before it starts to lose its resilience and can crumble.

Some of the properties of cork include lightness, impermeability, elasticity, low conductivity, and durability. These are some of the reasons that manufacturers have utilized cork over the years.

Not to mention the fact the since the harvesting of cork doesn’t kill the tree, it is a sustainable resource.

What is the history of cork?

Cork has been harvested for over 2000 years and has been commercially used since the 1700s. The ancient Greeks were the first to start harvesting cork in the manner that is seen today. Cork was first seen used as a stopper in 1688 for champagne bottles. And in 1892, cork stoppers were being mass produced. Plastic stoppers later became the industry standard in 1955.

In the late nineteenth century, an American developed the process of agglomeration. This is the process in which waste cork from stoppers is combined with a binding agent to create a more usable product. This allowed for other applications of cork and opened the door for new opportunities for the material in the marketplace.

The cork oak is now a protected species in the Mediterranean. The harvesting of cork has been legally controlled in Portugal since the 1600s. There are restrictions on harvesting to ensure the sustainability of cork in the region.

There are several threats to the cork oak today. These include deforestation, agricultural encroachment, disease, and climate change. Over the years, the market for cork has declined. This is due to wine makers using plastic corks. As such, many of the protections on the cork oak have decreased.

Cork oak forests are also home to other endangered species. The Iberian lynx, Iberian imperial eagle, Barbary deer, and other many fungi, ferns and other plants have made a home in these forests. If the cork forests were to disappear, so too would these animals. Not to mention the economic loss of the cork industry. In Portugal alone, wine stoppers have historically made up 72% of the cork industry.

Cork is one of the few sustainable and environmentally friendly wood products out there today. It has shown that it has a wide range of uses in the marketplace. Being a natural resource gives cork an edge over the man made varieties. It is important that this resource be understood so that it can be properly utilized in the future.