Campaigning for cork

By Lea Keiper, 17, TUNZA magazine intern, 2011

Cork has been the main material of wine stoppers since 1700. But in recent years, plastic stoppers and screw caps have gained a stake in the global market. TUNZA looked into the issues.

© Clive Muir,

© Clive Muir,

Natural cork stoppers

Some 2.2 million hectares of cork oak forest – mainly in Mediterranean Spain and Portugal – produce an annual global harvest of about 300,000 tonnes of cork. The cork oak must be 25–30 years old before its bark can be collected and the first two harvests are usually of minor quality. But a mature tree can produce 40–60 kilos of cork every 10–12 years for the remainder of its 200-year life. The harvesting is done by hand and does no harm to the tree. In fact it is good for the environment as a whole: it triggers the tree to absorb more carbon dioxide as it re-generates its bark; it offers a sustainable livelihood to local people; cork products are easily recycled; and the cork oak forests are prime habitat for endangered species including the Iberian lynx.

But real cork now accounts for only 60–70 per cent of wine stoppers, with synthetic stoppers and screw caps gaining in popularity. This is partly because they are a quarter of the price of natural corks, but also because there is less risk of the wine becoming tainted – or ‘corked’ – even though the risk is, in any case, quite low and the taint often minor.

Synthetic stoppers

Available since 1993 and accounting for 5–10 per cent of the global market, synthetic stoppers are made from plastic compounds that are designed to look and ‘pop’ like a natural cork. However, while they carry no risk of tainting the wine, they offer less protection against oxidation. Although not biodegradable, they are generally recyclable, but the plastic is usually only accepted by recyclers in areas where demand justifies the recycling of this kind of plastic.

Screw caps

These are made of aluminium and have a 15 per cent share of the world’s bottle stopper market. They form a tighter seal and therefore keep oxygen out of the wine for longer than either synthetic or natural corks, maintaining the wine’s quality and ageing capacity – but only for about 10 years, according to one study. They also contain a plastic seal in the top of the screw cap, and recycling is difficult.

Environmental impacts

Studies on the environmental impact of the various stoppers find that the benefits of cork outweigh the advantages of its aluminium and plastic alternatives in almost all areas (see table below). Regrettably, despite the efforts of manufacturers and recyclers, plastic stoppers and aluminium screw caps often end up in the sea, endangering marine life and contributing to the ever-growing islands of ocean garbage. In addition, synthetic stoppers threaten the conservation of cork oak forests: without the cork market, the forests are likely to degrade or even disappear.

TUNZA concluded that it is time to take a stand. It is usually impossible to tell whether a bottle seal hides a synthetic or natural cork, and not always obvious whether it is a screw top, so companies should be asked to give this information on the label of each bottle. This would enable consumers to make an informed decision before buying, and give them the chance to actively support the environment instead of harming it.

The environmental cost of cork relative to aluminium and plastic wine stoppers

Environmental indicator Cork Aluminium Plastic
Non-renewable energy consumption 1.00 4.33 4.87
Water consumption 1.90 1.00 3.06
Greenhouse gas emissions 1.00 24.24 9.67
Contribution to atmospheric acidification 1.00 6.15 1.54
Formation of photochemical oxidants 1.00 4.04 1.48
Eutrophication of surface water 1.00 1.10 1.52
Production of solid waste 1.00 1.99 1.57

Source: Amorim/PricewaterhouseCoopers.

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This post is also available in: French, Spanish