What is cork?

CORK OAK - TREE
Cork oak is a dicotyledonous plant of the beech family (Fagaceae), whichalso includes the trees known to us as chestnut and beech.
     This botanical family includes oak (Quercus). The oak genus contains over 600 individual species, with oak tree being their typical representative. The wood, bast or fruit of many of these trees are of great economic interest.
      All species of the genus stand in the shadow of Quercus Suber L., as the cork oak is called in scientific terms. Cork oak is the only cork-producing oak. No other tree grows such strong and resistant bark.

CORK OAK - ITS COMPOSITION
Cork oak is a woodland tree species, which exists in a vast range of forms,because it has dozens of varieties. The individual varieties can be distinguished by certain peculiarities of the heads, leaves and fruit.
In order to study the composition of cork, it is necessary to focus on the roots, trunk and head of the tree. Soon after germinating, the cork oak acorn grows the main root, known as the taproot. This root is perpendicular and deep, as much as the quality of the soil permits,allowing the trees a firm hold. Later, the main root is accompanied with various side roots, which can grow to great lengths in the side direction. These roots gradually part and become thinner, until their thickness is comparable to that of a hair.

Initially,the root grows actively, which explains the natural regeneration of cork oak under nearly hostile climatic and soil conditions.
On the other hand, unprotected roots, especially in places very near to theconnection of the root to the trunk, develop cork similar to the cork of the trunk.
The part close to the ground where the tree trunk divides from the roots is called the trunk base.

Cork oak has the ability to regenerate its bark. This provides the possibility of peeling the bark without harming the tree. The tree is at home in the Mediterranean area.
What an encyclopaedia tells us about cork...
 

QuercusSuber L (the Latin name of cork oak) lives to be up to 180 years old,which means that it allows for at least 17 harvests. The world production of cork is approximately 340 000 tons per year; out of which Portugal produces over 55 %

The first peeling (virgin cork) can be done after the oak tree reaches theage of 25 years and the minimum girth of 70 cm (27,5 in). The subsequent harvests of cork bark are collected after 10 – 12 years, in the summer months. Only during the third harvest does the bark have the desired quality. Cork bark grows and is harvested in various qualities depending on the climate conditions and on the geographical location.  The differences in quality can be seen clearly in the raw products – cork stoppers. See the picture Quality of cork.

The composition of cork
• Suberin (45%) – the main component of the cell wall, causing the flexibility of cork
• Lignin (27%) – binding compound
• Polysaccharides (12%) – a component of the cell walls determining the texture of cork
• Tannins (6%) – polyphenylene compound determining the colour of cork
• Ceroids (5%) – a hydrophobous compound ensuring the impermeability of cork
• Mineral water, glycerine, and other elements constitute 4%.
Cork cells are small, pentagonal or hexagonal prisms.
 
Cork is a natural product. Every cell contains an air-like gas (min. 50%); the cell walls consist of cellulose, suborn and wax. Suberin, alongwith wax, causes cork to be impenetrable to liquids as well as gases.This excellent quality of cork plus its amazing ability to regain its volume after compression makes cork into an ideal material for sealing bottles.