Oxygen transfer through cork stoppers

Abstract

During wine conservation in a bottle, the control of oxygen transfer from the outside environment to the wine inside the bottle is a key parameter that determines the wine quality. Many other factors can also influence the evolution of wine during postbottling aging, such as the composition of the wine itself, the temperature, the relative humidity, the storage position, as well as the amount of oxygen initially present in the bottle. However, the oxygen transfer is the most critical factor. For this reason, the choice of the packaging and in particular of the stopper is crucial in providing the best conditions for wine aging. 

With the various types cork-based stopper currently used, an additional outer layer of a surface treatment product is always applied in the final step of the manufacturing process. The primary function of these surface treatments is to facilitate the introduction and above all the extraction of the stopper from the bottleneck, as they reduce the adhesion between the glass and the cork acting as a slippery agent. However, only a few studies have reported the effect of the coating agents on the transfer of oxygen through the cork-bottleneck system. 

A comprehensive study was carried out to investigate the critical role played by the interface between the stopper and the bottleneck on oxygen penetration into the bottle, as well as the effect of the surface treatment of the stopper. This was performed starting from the diffusion through the stopper alone and ending with a more complex system comprising the stopper covered by a surface treatment agent and compressed in the glass bottleneck. 

First, the compression of micro-agglomerated cork, at close to 40%, had a limited effect on the oxygen transfer, with a decrease of the oxygen diffusion by a factor of 1.5. 

Second, once a cork was inserted into a glass bottleneck without any surface treatment, up to 99% of the total oxygen transfer took place at the stopper-bottleneck interface. Third, when the cork surface was coated with a paraffin-silicone mixture, there was almost no oxygen transfer at the interface. A coating with a thickness of less than 1 µm thus provided an efficient barrier for the stopper-bottleneck interface system to act against gas transfer at the interface. In addition to its initial role of ensuring easier uncorking, the surface coating therefore confers an additional and unexpected barrier efficiency to the wine sealing system.