Cork is a material obtained from the bark of a tree, the Cork Oak (Quercus suber L.), or more exactly from the outside layer of the trunk of the trees, from which is periodically removed without harming the tree, usually every 9–12 years (depending on the culture region), to assure the cork layer reached the minimum required thickness. The cork oak must be about 20–25 years old before its bark, called “virgin cork,” is removed for the first time; a second extraction of the cork is called “secundeira” (The many uses of cork). Only cork obtained from the third stripping, called “amadia” is suitable for manufacture stoppers (Cortiça); however, the first “amadia” cork is still very porous and irregular. In the same tree, the quality improves along the time.
Cork forests are essential for protecting the biodiversity of their respective regions. Forests full of cork oak trees can be home to endangered species, including the Iberian Lynx which is native to northern Portugal and southern Spain.
Cork tree is a slow growing, evergreen oak that flourishes only in specific regions of the Western Mediterranean (Portugal, Spain, Southern France, part of Italy, North Africa) and China because it requires a great deal of sunlight and a highly unusual combination of low rainfall and somewhat high relative humidity. Europe produces more than 80% of the world’s cork, being Portugal the major cork producer.
After being picked from the trees, the bark is placed on pallets ready to be boiled. The boiling process helps to soften and clean the bark. Finally, the cork is flattened, graded and cut into smaller more workable pieces.
How long does a cork oak tree live and yield cork?
The lifespan of the Cork Oak tree is between 150 and 250 years, each tree is able to provide around 12 harvests in its lifetime. Cork oak trees in yield between 3,000 and 5,000 corks per tree per harvest. Each year around 13 billion wine corks are produced. That means you need a LOT of trees.
Cork trees can live a couple centuries. However, the average lifespan for quality cork production is between 10 and 15 harvests (depending on the individual tree), after which the cork tree can become a lot less productive. Cork trees are strictly protected, however, and so you can’t simply pull it out, unless it has a serious virus or disease. Otherwise, it has to be left until it dies of natural causes.
How much cork does a tree produce?
On average each cork tree will produce around 1.5-2 arrobas of cork each harvest. An arroba is a special measurement unit which equates to 15 kilograms (so 23-30 kilograms per tree). Of that, only 5-10% will be suitable for the very top quality wine corks; the rest will be used for cheaper cork closures (or sometimes conglomerate wine corks) and other cork uses like badminton shuttlecocks, shoes and tarmac.