An industry trial provides further evidence for the role of corks in oxidative spoilage of bottled wines

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Abstract
Commercially available corks were tested for oxygen permeability and for the presence of oxidants by observing the change in concentration of antioxidants and the extent of browning in white wines stored in bottles with different closures. Bottles (375 mL) filled with a Semillon-Chardonnay blend were sealed with either a roll-on tamper-evident (ROTE) aluminium screw cap closure with a tinfoil laminate wad, or a combination of ROTE + cork, or cork alone. Both peroxide- and chlorine-washed corks, each from three different suppliers, were used in the trial. The bottles were filled, closed and stored in air under controlled conditions for 16 and 22 months. At each occasion, sample lots of 24 bottles of each closure type were analysed. Four types of corks, chlorine- and peroxide-washed corks from two of the suppliers, had greater oxidative capacity than those from the third supplier and the ROTE closure alone. The seals provided by three of the four types of closure with increased oxidative capacity were also permeable to oxygen. Only some of the seals provided by the peroxide-washed corks, and none of the seals provided by the chlorine-washed corks, from the third supplier appeared to be permeable to oxygen compared to the ROTE closure alone. In all cases where permeation was observed, the extent of oxidation caused by this characteristic was highly variable amongst corks within a given batch. In contrast, the effect of an increased oxidative capacity in cork appeared to be similar whether observed amongst corks from within and amongst batches, and irrespective of cork type and supplier origin. The results of this study shows the incidence of these defects in corks that are commercially available to winemakers in Australia.

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