Portugal's cork industry is so vital to the country's economy that it is illegal for a landowner to cut down a cork oak tree. "Bark police" patrol forests to prevent land clearance and to stop the bark being peeled too early in the growing cycle.
But the industry is at risk because of the growing use of plastic corks for wine bottles. The reason is that wine can become tainted by 2,4,6-trichloranisole (TCA), caused by micro-organisms in the natural cork combining with chemical contaminants used in the production process to kill bacteria.
Plastic stoppers, regarded as superior by winemakers, have been developed in the United States.
If cork farmers stop tending the vast oak forests of southern Europe, environmental groups such as the Royal Society for the Protection of Birds argue that air pollution will skyrocket and crucial habitats will disappear.
Luis Palma, a biologist and lecturer at the University of the Algarve, said: "Whether it is dense or sparse, with or without undersoil, cork woodland is the most important for biodiversity, particularly for endangered species. It is one of the most significant in terms of conservation. Cork forests are maintained and protected by law because they are economically important."
There are many misunderstandings about cork, Palma says. Trees are not cut down to produce cork, nor being stripped too often. "The cork can't be extracted too often - that wouldn't make sense. It is essential to get a sufficient thickness of cork so it can be transformed into bottle stoppers. Cutting it too soon would be counter-productive.
"If you abandon cork you will risk a million hectares of woodland. We must retain corks in bottles to keep a part of Europe's biodiversity safe."
But for consumers the wine takes precedence. Christian Butzke of the department of oenology and viticulture at the University of California-Davis, said TCA is one of the most powerful aromatic components in nature. "Less than one tablespoon of pure TCA could destroy all the wine produced in the US."