The Romans had already discovered the properties of cork and used it to seal wine amphorae. The use of this material was then abandoned for a long time, until, with the improvement of glass bottles, the first factories sprang up in Provence, towards the end of the seventeenth century: at the same time the legendary Dom Perignon found in it the ideal material for corking his Champagne.
Cork is obtained from the Quercus Suber, or cork oak, a tree that only begins to bear fruit 20 to 30 years after planting. In fact, the first extraction occurs when the plant has reached a circumference of 60 centimeters at a height of 130 centimeters above the ground. However, the proceeds from the first harvest – called “male” or “cork” – are of little value and cannot be used for the production of one-piece caps. Only from the second extraction-which must be carried out at least ten years after the first one-is cork known as “female” or “gentile,” the one of better quality.
Cork – a material with a very low specific weight (about 0.20) – consists of a fabric of cells overlapping in orderly and regular planes, made of cellulose – in the inner part – , lignin on the outside and a layer of suberin in the middle part. The latter, which makes up a large part of the cell membrane, is the organic substance that gives cork the properties that make it ideal for sealing wine bottles: strength, almost total inertness and impermeability, plasticity, flexibility, adherence, combined with easy workability and remarkable durability (a good cork holds up to 20-25 years: after that, it is best to replace it, re-corking the bottle and filling it with wine of the same type to avoid oxidation).
The substantial presence of soluble tannins in fresh cork, which would be readily released to the wine, is removed through the purifications of industrial preparation: first a double boiling of the planks (previously aged 6 to 24 months) and then fouling, during which the corks are placed in rotating and suction cylinders that remove dust and impurities.
Then the caps are sterilized in special solutions, dried to bring the moisture content to 6-8%, and lubricated. This operation, necessary to facilitate the entry of the cork into the bottle neck and to reduce the formation of dust, traditionally consisted of copious kerosene coating: today kerosene has been almost totally replaced by chemically inert silicone preparations.