Where do we get cork?
Cork is riddled with tiny holes like a lump of pumice, which is a rocky mineral. It floats on water like a foam rubber sponge, which is a man made synthetic. But cork is neither a mineral nor a man made substance. It is a product of the plant world. The cork we use as bottle stoppers, fishing floats, packing material, baseball stuffing and paper¬ thin cigarette tips all grew from tiny acorns.
The cork tree which gives us endless varieties of frothy cork is an oak and, like all the 275 different oak trees in the world, it grows from an acorn. (roves of cork oaks are cultivated in Portugal, France, Spain and North Africa and every cork planter must be a very patient person.
Growing trees produce nothing for their first 25 years. The first harvest is loose, crumbly cork useful only for packing grapes. The planter must wait another ten years for his next harvest when he can expect each tree to yield several hundred pounds of fairly good cork. Ten years later, harvest time comes around again and the 4.5 year old tree will be in the prime of life, Each will yield about 500 pcunds of the finest cork and they will repeat this harvest every ten years for another 100 years.
The cork tree is a live oak which keeps its old leaves until they are replaced with new ones. It may stand 60 feet tall, Its bulky trunk and branches are rough and gnarled with thick bark. This foamy bark grows in two layers and the outer layer of bark yields the harvest of cork.
The outer bark of the cork tree, like all parts cf a plant, is made from boxy little cells. The cell walls are thinner than thin but they are crisp and firm with resins. A cork bottle stopper contains millions of these boxy cells filled with nothing but air.
The thin cell walls make up less than half of the bulk of the cork, which is why it is light enough to float.
When the outer bark is peeled from the tree, the corky material is boiled to remove its juicy sap and tacky resins. When dried, only the papery cell walls remain and the microscopic cells are packed tightly together, each trapping its pocket of air. These sealed pockets of air keep the outside air from passing back and forth through the cork. For this reason, sheets of cork are used as insulating material arid we find them packed around furnace pipes to keep the hot air from escaping.
The cork tree belongs to the plant genus Quercus, a scientific term borrowed from the Latin name for an oak tree. Its stately cousin the white oak has the scientific name Quercus alba, the red oak is Quercus rubra. The scientific name Quercus suber means oak and cork tissue which makes it a reasonable title for the sturdy cork oak.