The process of making a natural cork begins with the careful husbandry of the cork forests, which is divided into two main areas — care of the soil and of the tree itself.

In recent times, due in part to increasing pressure from cork manufacturers, there has been greater emphasis on forest management by plantation owners.

Amorim Florestal, the group's specialist cork purchasing unit, plays an active role in forest management to ensure it purchases the best quality raw material. It only buys from growers complying with the industry's International Code of Cork Stopper Manufacturing Practice and has records going back five decades to help it identify and select the best quality cork bark.

In Portugal, the forests are protected by law and the felling of cork oaks is not permitted save for essential thinning or to remove trees decrepit with age.

A cork oak begins life as an acorn, which may germinate naturally in the forest or under controlled nursery conditions.

Growth is slow and gradual. The tree needs a lot of light, relatively little rain, a degree of humidity and thrives up to 1400 metres above sea level.

Tilling the soil periodically and clearing undergrowth improves tree vigour and helps to ensure the sustainability of the forest's growth.

The forest is selectively thinned to remove aged trees, maximise tree growth and avoid the depletion of soil nutrients.

The bark of mature cork trees is harvested just once every nine years. Cork trees are not regarded as mature enough for bark harvesting until they are at least 25 years old.

Harvesting requires the delicate stripping of the outer bark by skilled workers using specialised cork axes.

The stripping is carried out in spring or summer when the tree is growing strongly and the bark comes away easily from the trunk. The tree is temporarily debilitated by the stripping but the outer bark regenerates and the tree continues to flourish.

Pruning, which is strictly regulated, assists saplings to develop a tall straight trunk and well-formed boughs. It also maintains the form of mature trees and revitalises older trees.

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