On Cork

Searching for cork in the Parque Natural de La Sierra de Espadán.

On Cork
By guest author Avery Bartlett-Golden
 
Often when thinking of oak trees, an image of tall stately trees comes to mind. However, the oak genus has a strong connection to wine - from the barrels used to age wine in to the corks sealing the bottles. Quercus suber is the tree from which cork is harvested.
 
The cork tree, Quercus suber, is an interesting plant, intermediate in size with deeply fissured bark and evergreen leaves. At home in the Dehesa of Spain and Portugal as well as the Mediterranean Rim, it has evolved a unique strategy to resist the regions’ forest fires. Commercially used as an insulator, cork bark also functions as insulation for the tree, insulating the trunk and branches from the heat of forest fires and allowing swift recovery. While very rare, the bark can grow to 20 cm thick if the tree is left to grow naturally. Limited in range primarily by the presence of suitable acidic soils, Q. suber requires around twenty years before the first harvest of bark, and depending on the region, nine to fifteen years to reach a suitable thickness necessary to produce wine bottle stoppers.

Last semester I took a class called Protection of Forest Health: Wood and Cork. As part of the class, we took a field trip to the Parque Natural de La Sierra de Espadán to learn about cork. Near the park we visited the Sierra Espadan Corks company and watched the cork manufacturing process first hand.

View of the Parque Natural de La Sierra de Espadán.

The first peel of bark from the cork tree is usually too rough for making stoppers and is commonly used as a decorative substrate for orchids and other epiphytes in cultivation. Planks of bark to be used for stoppers are usually dried from six months to a year before being boiled in water to clean and improve the workability of the cork.

Once dried, the planks are cut in strips the length of a stopper and manually or mechanically punched. The blanks then get sorted optically by machines and by hand into differing grades and defective stoppers are removed. The blanks are then labeled with ink for red wines and branded for white wines where ink could potentially bleed. Finally, the blank is usually waxed with paraffin or silicone, although some manufactures use naturally derived paraffin of beeswax.

After sorting, washing, trimming, stamping, and waxing, the corks are finished.

The Sierra Espadán Corks company is one of the very few to use FSC (Forest Stewardship Council) certified cork which ensures that the product comes from sustainable forests. The company also uses cork from the natural reserve, one of the only parts of Valencia where cork grows. The conditions here require fifteen years between peels but the end result is a special cork sought after for some of the finest vintages of Spanish wins.
 
After seeing the factory, we hiked through part of the Sierra Espadán reserve and observed cork trees in different stages of growth. We also noted fungi and diseases in Q. suber and intermixed pines. This was a grand experience in very gorgeous country. 

Guest author Avery Bartlett-Golden is a Horticulture Science major at North Carolina State University. He is currently studying abroad in Valencia, Spain.

Students walking through parts of the Parque Natural de La Sierra de Espadán near Valeancia, Spain.