SERREJÓN, CÁCERES, SPAIN – JUNE 28, 2015: Workers extracting the cork from the trees and transporting it with horses.
The Cork Tree
Cork is the outer bark of an evergreen oak of the genus and species Quercus Suber (oak cork). Forests of oak cork trees are carefully monitored and cultivated, and act as a renewable source for this remarkable material.
A cork tree regenerates its precious outer layer 12 or 13 times during its 150-year lifetime. The first stripping of the cork bark occurs when the tree is between 15 and 20 years of age, with subsequent yields at 9 to 10 year intervals.
The Cork Harvest
Harvesting cork is the operation of removing bark from the tree during spring or summer. This is the time of year that the tree is engaged in rapid growth. The tender, newly generated cork cells break away from the cambium easily and without damage.
The process is temporarily debilitating but the outer bark quickly regenerates and the tree continues to flourish. Studies show that regular harvesting generally improves the trees health and vigor. Stripping cork is a delicate operation that is performed by hand with traditional tools and methods. Despite periodic attempts, there is no mechanized or automated process that can compare to traditional harvesting techniques.
Harvest difficulties occur if the process is not carried out when the tree is in full growth. As soon as it is evident that the cork is being stripped too early or too late in the season the stripping is brought to a halt, a year’s delay in cork extraction is preferred to damage to the tree. The delicate operation of stripping cork has been performed in the same way for decades. Experienced cork strippers use a specialized cork axe to slit the outer bark and peel it away from the tree. This continues to be the quickest and cleanest method available.
The harvested cork bark is removed from the forests, and are left out in the open air for six months. This weathering process actually improves the cork’s quality. The cork bark is then sorted by quality and size. The first use is for the extraction of cork stoppers to meet the demands of the world’s wine and champagne industries, which use over 13 billion cork stoppers annually.
The remaining cork (called “blocker waste,” although it is perfectly good material!) is then ground up and processed to be used in the production of agglomerated cork and cork & rubber compounds. These materials are used in a variety of applications from construction and gaskets, to bulletin boards and decoration.
The Growing Cycle
Cork is harvested in a steady cycle that promotes healthy growth to the tree over its expected lifespan of over 200 years.
Typically, virgin cork is not removed from saplings until the 25th year, and reproduction cork (the first cycle) may not be extracted for another 9-12 years. Cork suitable for wine stoppers is not harvested until the following 9-12 year cycle, so farmers have invested over 40 years before natural wine corks are produced.
The first harvest produces cork of a very irregular structure. This is called ‘virgin cork’. The second harvest brings ‘reproduction cork’ – a material with a more regular structure and less hard. This ‘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 more than 150 years. This is the type of cork that is most commonly used for wine stoppers.
A Sustainable Industry
Today, the center of the world’s cork oak forest is concentrated on Europe’s Iberian Peninsula and the adjacent Mediterranean basin, where soil, temperature, rainfall and wind conditions are ideal. European forests account for two-thirds of cork oak production, while North Africa produces the remaining one-third. The total land surface occupied by the cork oak forests is 2.2 million hectares (5.434 million acres), of which Portugal and Spain represent 56%.
The cork industry employs more than 15,000 workers in factories devoted to converting raw cork and cork byproducts into commercial products. In addition, the industry employs thousands of seasonal workers for the cork harvest and the maintenance of the oak forests.
In the prime cork-growing region of Portugal, cork oaks and their harvest are protected by law in order to protect this valuable resource and ensure the quality of the harvest.