Chapter 5 - The extraction of cork

Abstract

The extraction of cork, or cork stripping, is done manually by cutting large rectangular planks and pulling them out from the tree. The operation takes advantage of the fragility of the phellogen and of the newly formed cork cell layers in order to be able to tear the cork layer out of the tree without damaging the inner bark and cambium. The industrial requirements for the raw material derive from its use, which nowadays is directed in the first option to the production of stoppers. Therefore, a sufficient thickness is necessary, that is, the cork planks should be over 27 mm thick, and defects such as excessive discontinuities, that is, deep fractures, cannot be present. This is the reason why virgin cork and second cork, the corks obtained, respectively, from the first periderm and from the first traumatic periderm, are not used for stoppers. The operation of cork stripping and of the subsequent field and mill yard storage are detailed in this chapter and graphically exemplified in a sequence of pictures. The effect of cork removal on the tree physiology and radial growth is also analyzed. The characterization of the different types of cork raw materials that are obtained from the exploitation of cork oak stands is then presented in conjunction with their implications in the industrial processing.