Variation of cork quality for wine stoppers across the production regions in Portugal

Cork production and technological quality were characterized following a field sampling covering the whole area of cork oaks in Portugal (six regions), with one site per 20,000 ha of cork oak area (30 sites), using samples taken from the tree at the time of cork stripping (20 trees per site). The following quality parameters were determined: thickness of the raw cork planks, calliper of the cork planks after boiling, cork growth index, i.e., growth of the first 8 complete years, density and porosity. The cork growth index was 28.6 mm, with significant differences between regions and sites within regions. A production cycle of 9 years was applied to 51% of the trees with annual productivity of 0.93 kg m⁻² year⁻¹ of debarked surface, 30.3 mm raw cork plank thickness, 33.9 mm corkboard calliper, 251 kg m⁻³ density and a porosity coefficient of 5.8%. For all the cork quality parameters analysed, the regions and sites within regions were a significant factor of variation. This research covers the natural variability of cork production features for industrial processing, namely for the production of wine stoppers. It is the most extensive work characterizing the geographical variation of cork as an industrial raw-material. The results are useful for optimizing the production cycle and for improving management practices and regulations.