Cork is the outer bark of the cork oak tree, which grows mainly in the Mediterranean region. This remarkable tree has a bark whose properties and method of regeneration are unique in the entire plant kingdom. The unique composition of cork raw material with more than 40 million air-filled cells per cubic centimeter makes cork a natural sound and heat insulator. Each cell contains a gas similar to air (min 50%), cell walls are made of cellulose, suberin and wax. Suberin together with wax makes cork impermeable to liquids and gases. This excellent property, together with excellent regeneration after compression, makes cork an ideal product for closing bottles.
Cork oak
Cork oak is a dicotyledonous plant from the beech family (Fagaceae), which also includes species found in our latitudes (e.g. chestnut and beech). All other species, however, are surpassed by the cork oak with the Latin name "Quercus suber L.", which occurs in the Mediterranean region. It is the only oak that produces cork. No other tree produces bark as strong and durable as the cork oak. Cork oak has the ability to regenerate its bark, which allows it to be peeled without damaging the tree. Very important for the cork oak are the roots, which enable a firm attachment to the soil. Soon after germination, the acorn produces a main root which is vertical and grows deep into the ground as far as the nature of the soil permits. During growth, various lateral roots are added to the main root. They are gradually divided and thinned to the thickness of a hair. The root actively grows from the beginning, which explains the natural regeneration of the cork oak under almost inhospitable climatic and soil conditions. Exposed strong roots, especially in close proximity to the trunk, form a cork and trunk. The transition between the trunk and the roots is called the base of the trunk. A cork oak lives to be around 180 years old, which means it allows for around 17-20 harvests of cork bark. The first peeling of the "virgin bark" can take place at the age of around 25 years, when the tree reaches a circumference of at least 70 cm. The subsequent removal of the bark is repeated after 9-12 years, always during the summer. Only at the third peeling does the bark reach the required quality. Bark harvesting has been done in the same way for centuries, by hand, without the need for environmentally harmful mechanization. Cork bark grows and is peeled in different qualities depending on climatic conditions and geographical location. The differences in quality can be seen very well on the primary product - cork stoppers. World bark production is around 340,000 tons per year, of which more than 55% is produced by Portugal.
Composition of cork
• Suberin (45%) – the main component of cell walls, causes cork flexibility.
• Lignin (27%) – connecting compound.
• Polysaccharides (12%) – a component of cell walls determining the texture of cork.
• Tannins (6%) – polyphenylene compound determining the color of the cork.
• Ceroids (5%) – a hydrophobic compound ensuring the impermeability of the cork.
• Mineral water, glycerin, and other elements represent 4%. Cork cells are tiny, pentagonal or hexagonal prisms.
Microscopic structure, made of cells filled with air and wax (suberin),
makes cork the best natural heat and sound insulator.
