More than you ever wanted to know about cork trees

As you ride through Portugal, particularly the Alentejo and Algarve regions, you will see gnarly, reddish rather sculptural but ugly oak trees sporting large numbers in white paint on their trunks.

These are the Quercus suber, an evergreen Oak tree, dropping acorns and growing a thick bark that is commonly known as cork. It is the primary source of cork for wine bottle stoppers and a multitude of other uses, such as cork flooring and as the cores of cricket balls.

Portugal produces about half the world output of commercial cork! Here's a brief summary of the billion dollar cork industry in Portugal.

The Trees

Cork Oak is native to southwest Europe and northwest Africa where it is well suited to this climate: An abundant and evenly distributed rainfall, short summer dry periods tempered by atmospheric humidity, very mild winters, clear skies and plenty of sunshine, very permeable, moist and deep siliceous soils. 

A fascinating and important tree, Cork Oaks can support diverse ecosystems and for this reason are a protected species, with their harvesting process being heavily legislated and regulated in Portugal. The species, which covers approximately 8 percent of the total area of Portugal and constitutes 28 percent of its forests, grows best in the central and southern parts of the country where the largest stands supplying the greatest percentage of high-grade cork are to be found.

The Harvest

Every year from Mid May to Mid August, well-trained seasonal harvesters stage their harvest of the Cork Oak in Portugal. Once a tree is about 25 years old it can be harvested for its ‘virgin cork’ and then every 9 years after the cork ‘bark’ is harvested, and the year is marked on the tree with the last number of that year (ie. A tree harvested this summer will be painted with a 9). Portuguese law prohibits stripping the trees more than once every nine years in order to protect the species. 38 year old bark (roughly the third harvest) is when the bark becomes of high enough quality to produce wine stoppers. 

The harvest of the height of the tree is determined by the diameter, if the tree is 1 metre in diameter, you can harvest three metres of the height of the tree. A Cork Oak lives for about 150 - 200 years on average meaning that it will be harvested about 15 times over its lifecycle.

The Process

After harvest, trucks carry the cork to plants to be stabilised and prepared for cork stopper and other production processes. First, the slabs of bark are pressed under concrete slabs for 6 months, the cork is then sterilized using a big boiler. Next, the cork is classified into quality grades for different uses, with experienced cork workers visually assessing the quality of the bark. Wine cork stoppers are made in the north of Portugal and then exported all over Europe. The residual cork wood can be used for flooring and building materials (see other uses below) but also a new market in cork-based eco-fashion has become a trend in recent years.

The Industry

The European cork industry produces 300,000 tonnes of cork a year, with a value of €1.5 billion and employing 30,000 people. Wine corks represent 15% of cork usage by weight but 66% of revenues. 

Of the producing countries, Portugal, plays an important part in the industrial utilization of cork, and so rightly occupies the foremost position. It has 500 factories, which employ about 20,000 workers, equipped with the latest machinery and utilizing the latest technological advances, enabling the industry to meet the demand for any product. This industry produces stoppers, discs, different types of floats, shoe soles, printing paper, cigarette tips, bath mats, table mats, hat bands, fishing rod handles, different kinds of packing. Cork wool is produced for cushions and mattresses and granulated cork employed chiefly as insulating material in ship-building, as a protective packing for fruit and eggs, and as tubing for plastic substances. 

The Biggest Tree

Near the Portuguese town of Águas de Moura the Sobreiro Monumental (Monumental Cork Oak) is located, a tree of 234 years old, 16 metres (52 ft) tall and with a trunk that requires at least five people to embrace it. It has been considered a National Monument since 1988, and the Guinness Book of Records states it as the largest and oldest in the world.

Vanya Maplestone

Vanya is a part-time cycling tour guide, part-time food blogger/writer and full-time food savant. She also loves cork.