Cork produced from cork oak tree bark; see there.
The Assyrians, Egyptians and Greeks already knew the cork stopper in early antiquity. In some cases, cork stoppers were also used as closures for amphorae. Mostly, however, stoppers made of terracotta (clay) were used, which were fastened with string and then sealed with varnish, clay or pitch. The Roman author Cato the Elder (234-149 BC) wrote that the wine jugs had to be sealed with cork and pitch after fermentation. So the Romans already knew this type of closure, but it fell into oblivion again with the fall of the Roman Empire. Probably because the Iberian Peninsula, the main source of cork bark, was conquered by the Moors in the 8th century and dominated for a long time. Until the late Middle Ages, vessels were sealed with wooden stoppers dipped in oil and wrapped in hemp, pitch or wax.
With the development of glass bottles, glass stoppers were used first, but at the beginning of the 17th century the cork was rediscovered. The alleged inventor of champagne Dom Pérignon (1638-1715) also experimented with it. Due to different bottle neck sizes, the corks initially had a conical shape and were also only half sunk for easier removal. It was not until the development of usable corkscrews that they acquired a cylindrical shape and were now driven fully into the neck of the bottle. The cork then became the dominant type of closure for bottles from the middle of the 17th century, which led to a rapid boom in the cork industry.
The natural cork stopper is mainly made from the thick, outer bark of the most suitable cork oak "Quercus suber". More than half of the world production comes from Portugal, other countries are Spain, Algeria, Italy and Morocco. The trees, which can grow to a height of 10 m, can be used for about 200 years. But peeling is only possible for the first time when the tree is 25 years old; for bottle corks, the bark is even only suitable from the age of 45. A tree can be debarked around 15 times at intervals of 9 to 12 years. The bark is seasoned for at least a year, then boiled in water, pressed, cut into slabs and sorted according to quality. Strips are cut from these, from which the cylindrical plugs are punched out. They are produced in a length of 38 to 60 mm; longer corks usually also mean a higher wine quality. The blanks are smoothed on the front surfaces and ground round. This is followed by bleaching and impregnation with a...