Cork is harvested from the Cork Oak tree, Quercus suber L., which is found predominantly in the Mediterranean, with Portugal and Spain producing 82% of the world's raw cork. Italy, France, Morocco, Algeria and Tunisia account for the remaining18%. The majority of the cork harvest is used for wine stoppers, with lower quality cork material going into shoes, gaskets, linoleum and agglomerated products.

Natural cork has a unique structure. The bark of the cork tree is made of tiny cells, each a 14-sided polyhedron with intercell spaces filled with oxygen or nitrogen. A single cubic centimeter of cork contains approximately 40 million of these cells. This cellular structure allows cork to recover 85% of its initial volume almost immediately after compression, and 100% within 24 hours. Cork also has a high coefficient of friction and is almost impermeable to liquids.

Cork is harvested in a steady cycle that promotes healthy growth to the tree over its 200-year lifetime. Virgin cork is first removed when the tree is 25 years old, then followed by the harvest of what is called reproduction cork (first cycle) after another 9-12 years. It is another 9-12 years before wine-suitable cork can be harvested. In the mature tree, cork bark is cut and harvested in the form of planks (from the main trunk) or tubes (from branches).

The cork bark is stacked and left to age in the forest before being boiled to expand the natural cellular structure. After the cork has dried to 20% moisture content, it is hand punched (higher quality cork), or machine punched (lower quality) into wine bottle cork shapes.

Modern washing systems using a variety of chemicals sanitize the corks against bacterial growth, with some manufacturers utilizing new technologies such as irradiation as a final weapon against the potential of TCL growth which results in cork taint. Corks are then sealed in bags containing inert gases before being shipped to wineries.

The 2000 cork harvest from Spain and Portugal yielded 250,000 tons of cork bark, an increase from last year, due in part from ideal growing conditions and the approaching high point in the 9-year production cycle. This is good news for winemakers, since demand has been rising in the past few years, along with the price of quality cork stoppers. James Herwatt, vice president and general manager for Cork Supply USA, said, "As a result of the increased harvest, winemakers can expect overall cork prices to stabilize."