Corks

Corks are closures used to seal bottles, and other containers, most notably wine bottles. They can be made from the bark of the cork oak (Quercus suber) in natural form, or from synthetic or composite materials designed to imitate cork’s properties. Natural corks are valued for their elasticity, compressibility, and low permeability to gases, which supports controlled oxygen transfer during wine aging.

Natural corks are produced by harvesting cork from mature trees, typically every 9 to 12 years. The harvesting does not kill the tree; the bark regrows, allowing repeated harvests over decades. The cork industry is concentrated in Mediterranean countries, especially Portugal and Spain, where vast cork oak landscapes provide habitat and help prevent land degradation.

Other cork closures include agglomerated corks, made from cork granules bound by binders; and synthetic or composite corks, which can offer uniform performance and lower taint risk. Champagne and sparkling wine closures use long natural corks with a wire muselet to withstand high internal pressures; some producers also employ synthetic alternatives for sparklers.

Wine closures influence aging by regulating tiny quantities of oxygen; natural corks typically permit slow gas transfer, while synthetics may be more airtight. The choice of closure affects flavor stability, aging potential, and bottle variation. Cork taint, caused by compounds such as 2,4,6-trichloroanisole (TCA), can impart musty aromas and is a well-known risk, though its incidence varies and is generally a minority of bottles.

Environmental and economic aspects: cork forests (montados) support biodiversity and protect against erosion; cork harvesting is relatively low-energy and can be sustainable when managed properly. The cork industry remains an important regional employer in Portugal and Spain, though the rise of alternative closures has diversified the market.