How Cork is Made

Cork is composed of suberin, a hydrophobic substance, and because of its impermeability, buoyancy, elasticity and fire resistance, it is used in a variety of products (most common is wine stoppers). Cork consists largely of empty space because of its honeycomb-like structure. Its density is one-fourth that of water. Uses of cork consist of flooring material, shoe insoles, roofing panels, gaskets, safety helmet liners, bottle and wine stoppers, dartboards, bulletin boards, and cores for golf balls and baseballs. Cork is harvested from the cork oak tree, most commonly found in southwest Europe and northwest Africa. Cork is extracted only in summer months when the cork can be separated from the tree without causing permanent damage. When the tree reaches 25-30 years of age and about 24 inches in circumference, the cork can be removed for the first time (the first harvest almost always produces poor quality cork). Subsequent extractions usually occur at intervals of 10 years, though it can take up to 13 years for the cork tree to reach an acceptable size. Harvesters use a sharp axe to make two types of cuts : one horizontal cut around the plant (called a crown) at a height of about 2-3 times the circumference of the tree, and several vertical cuts called rulers or openings. To remove the cork from the tree, harvesters push the handle of the axe into the rulers. The sections of cork that is removed from the tree are called planks. The planks are then dried, washed, and cured over weeks or months to make the cork softer and more flexible. The best quality material is used to make natural cork products like wine stoppers. The poorer quality material may be ground and used to make composition or agglomerated cork often used to make floor tiles or corkboards.