CORUCHE, PORTUGAL (AFP) - In this natural forest northeast of Portugal's capital, centuries-old cork oak trees are bathed in sunlight, their thick greyish bark standing out among the greenery.
"Look at them, it's as if they were human, each one is different," forestry engineer Conceicao Silva says as she inspects tree branches.
This forest in the central Portuguese region of Ribatejo is a national treasure as the trees provide the raw material used to produce over half of the world's cork stoppers.
"This one is four years old," Silva says, touching a tree in the natural forest which measures about 1,300 hectares. The cork trees can live for as long as 300 to 400 years, but they "grow very slowly," she tells AFP. And the process to yield a usable, money-making harvest can take decades.
"It takes around 50 years for them to bring in money," said Jean-Marie Aracil with the French Federation of Cork Unions.
The first cork harvest, taken when the trees are between 25 and 35 years, won't yield usable cork, nor will the second, and only a third harvest, two decades after the first, is really productive.
But everyone accepts that time passes slowly for these cork trees - found mainly in Portugal, Algeria and Spain - that have been in use since the Ancient Greeks first closed wine jugs with them in 5 BC.
And traditional and technical corks are still the world's preferred way to seal bottles, despite inexpensive synthetic screwtops gaining market share in recent years.
CORK 'GAINING GROUND'
Portugal remains the leading producer of cork - seven of 10 wine bottles in the world are topped with Portuguese corks.
Just a few kilometres away from the forest in Coruche is a plant owned by Portuguese company Corticeira Amorim, the world's biggest cork producer.
Thousands of just-harvested cork parts dry over an area as large as a dozen football fields.
After six months of being left out to dry, the raw cork will be boiled in order for it to gain thickness and elasticity and to remove tannins, before it will be cut into strips and perforated as tops.
The corks will then be washed, dried, labelled and treated with paraffin or silicone to facilitate export.
Yet only about 15 to 30 per cent of the cork will be of sufficient quality to produce whole cork stoppers used to top fine wines, said Jose Pinto, the Portugal general director of French corkmaker Lafitte, based near Porto.
The other 80 per cent or so will be used for parts, half for plant boilers and the other half to produce technical stoppers - cork slivers glued together that are cheaper than traditional whole cork stoppers.
These stoppers, which look a lot like the traditional variety, are put on wines to be consumed within two to three years.
The caps are particularly popular in the United States, France and Italy among mass market wine makers, the main users around the world of inexpensive plastic or metal screwcaps.
More and more of these types of cheaper stoppers are being produced in Portugal as a way to gain back the third of the market share that has been lost to screwtops.
"The cork is gaining ground," said Carlos de Jesus, the marketing director of Amorim, which has concentrated production of its "Twin Top" brand of technical stoppers at one factory.
"Global wine consumption is increasing by 0.8 to 1 percent per year, Portugal's cork exports are rising by 2 percent a year, or 1.4 percent for cork stoppers".
"We are regaining market share," he said, adding that numbers like this haven't been seen since the early 2000s.
The main reason cork saw declining profits 10 years ago can be summed up with one word: "taint".
When cork caps leak, crumble or become infected with mold, it gives wine a musty odour called cork taint, a bad taste caused by the chemical trichloroanisole (TCA) found in cork.
Spoilage from taint is estimated to affect less than one per cent of bottles. It can lead to the complaint that a wine is "corked".
"We accept it less and less," Dominique Tourneix, the chief executive of French corkmaker Diam Bouchage, which specialises in the production of "taint-free" cork.
According to Tourneix, the biggest consumers of French wines - the Chinese, Japanese and Brits - "are much less tolerant" of cork taint, a feeling that has migrated to their neighbours.
"There used to be a huge tolerance (for taint), in Spain, France, Italy," Tourneix said. "It is no longer the case, especially when it comes to premium wines".
Technical corks have helped limit the problem and manufacturers have also invested heavily in research to detect taint.
"The 'premiumisation' of wine is a positive development for the industry," Jesus said.
Wine stoppers account for 72 percent of the value of the annual global cork harvest, according to the Portuguese Cork Association. Cork is also used for insulation materials, tiles, clothes and other industrial applications.
Portugal - which remains the industry's powerhouse, followed by Spain, France and Italy - will continue to promote the planting of cork oak trees, Aracil said.
After the huge summer forest fires, Portuguese authorities decided "to promote the planting of cork oaks whenever possible" as their insulating properties can act as a "barrier to fire spread."