Natural variability of surface porosity of wine cork stoppers of different commercial classes

Aim: The aim of this study was to characterize the variability and to quantify the surface porosity of wine cork stoppers of different quality classes. Methods and results : The porosity of 300 cork stoppers was characterized by image analysis on the lateral surface and tops. Porosity coefficient was 2.4%, 4.0% and 5.5% for premium, good and standard stoppers, respectively. The lateral surface of stoppers was heterogeneous with respect to porosity features: the tangential regions presented higher porosity while the radial regions had larger pores. Conclusion : The quality classes of cork stoppers can be differentiated by the mean values of the main porosity features of their surface. There is a natural heterogeneity of the porosity features over the external surface of cork stoppers that can be traced back to the biological basis of cork formation and the production process. Significance and impact of the study: Natural cork stoppers are the premium product of the cork industry, with worldwide recognition of quality and performance as wine sealant. Due to the large sampling and detailed observation, the results presented in this study may be used for reinforcing quality requirements, e.g., with definition of standards to improve the classification system. A better understanding of cork intrinsic variability and of the anisotropy of porosity features shown by cork stoppers is important for performance development