Cork
Winemaking · Beginner · 3 min read
Cork is a traditional bottle closure made from the bark of the cork oak, Quercus suber, a tree that grows mainly in Portugal and Spain. It has been used to seal wine bottles for centuries, and it is still the closure of choice for fine still wines that are intended to age in bottle. English sparkling wines, however, almost always use a crown cap or a technical cork alternative, because the long second fermentation and the lees ageing put stresses on a natural cork that it cannot easily survive.
Where cork comes from
Cork is the outer bark of the cork oak, a slow-growing evergreen tree that thrives in the warm, dry landscapes of the western Mediterranean. The tree is first stripped at about 25 years old, and then harvested every 9 to 12 years for the rest of its life, often for 150 years or more. The bark regrows after each harvest, making cork a uniquely renewable material.
Portugal produces around 50 percent of the world's cork, with Spain, Morocco, Italy, Tunisia and Algeria making up most of the rest. The cork industry is concentrated in the Alentejo and Ribatejo regions of Portugal, where the Amorim family runs the world's largest cork manufacturer, and where the cork oak forests (montados) are a recognised UNESCO-protected landscape.
Cork as a wine closure
For still wines, a good natural cork is flexible, compressible, and just permeable enough to allow a tiny amount of oxygen to enter the bottle, helping the wine age gracefully. A well-made cork is also a beautiful object, with a distinctive smell and a satisfying pop when drawn from the bottle.
The main drawback is cork taint, an off-aroma caused by a compound called TCA (2,4,6-trichloroanisole). Even a few parts per trillion can make a wine smell of damp cardboard or musty newspaper. Modern cork producers have reduced TCA incidence to under 1 percent of stoppers, but it remains a real risk and the reason many producers use technical closures such as screwcaps or agglomerated corks for certain wines.
Why English sparkling uses different closures
Traditional method sparkling wine spends 24 months or more in contact with the closure during the second fermentation and lees ageing. A natural cork in that position would be attacked by the high pressure (around 5 to 6 atmospheres) and by the sulphurous compounds in the lees. Crown caps, the kind used on beer bottles, are the universal choice for the second fermentation. After disgorgement, the bottle is sealed with a mushroom-shaped cork, often capped with a crown cap and a wire cage. Many English producers also offer a still version sealed with a natural cork for export markets that expect the format.
Alternative closures in the UK
English wine closures are usually either a crown cap, a technical cork, a screwcap (Stelvin) or a glass stopper (Vino-Lok). Crown caps are used for sparkling wines during the second fermentation. Technical corks, made from agglomerated cork granules, are a cheaper and more consistent alternative to natural cork for still wines. Screwcaps are increasingly common for early-drinking whites and rosés, especially at the everyday price point. Glass stoppers are a niche but growing choice for premium bottles.
The closure choice is partly practical, partly marketing. A screwcap signals freshness and modernity. A natural cork signals tradition and age-worthiness. A technical cork sits in between. UK producers consider all three when designing a new wine.
Cork and the UK supply chain
Most cork used in the UK is imported through Portuguese suppliers such as Amorim, Cork Supply Group and Portocork. The UK closure market is sophisticated: a major English producer might specify 49 by 24 millimetre natural cork, branded with the producer's name, sourced from a specific forest and graded by a taster. The whole supply chain, from Portuguese forest to English bottling line, typically takes 6 to 12 months from order to delivery.