Wine bottle closures: physical characteristics and effect on composition and sensory properties of a Semillon wine 1. Performance up to 20 months post‐bottling

A Semillon wine was bottled using 14 different closures: a screw-cap type, two grades of conventional natural cork, two 'technical cork' closures (natural cork with a synthetic component), and 9 closures manufactured from synthetic polymer material. Closure performance was evaluated for physical aspects (e.g. extraction force and energy, change in closure diameter, and ease of closure reinsertion), and for wine composition and sensory properties. Wine under the screw cap closure retained the greatest concentration of sulfur dioxide (SO2) and ascorbic acid and had the slowest rate of browning. For other closures the trend of SO2 loss relative to the screw cap closure was apparent from an early stage of testing, and was most evident in the group of synthetic closures, intermediate in the conventional corks, and least evident in the technical cork closures. The loss of SO2 was in general highly correlated with an increase in wine browning (OD420) and the concentration of SO2 in the wine at six months was a strong predictor of future browning in the wine, particularly after eighteen months. Neither the concentration of dissolved oxygen at bottling (0.6-3.1 mg/L), nor the physical closure measures were predictors of future browning. For several closures upright storage tended to accelerate loss of SO2 from the wine, but in many cases this effect was marginal. The closures differed widely in regard to physical characteristics, and in general synthetic corks appeared least 'consumer-friendly' in terms of extraction forces, energies, and ease of closure re-insertion, but there was a trend for natural cork closures to exhibit larger variability in physical characteristics than technical cork and synthetic closures. Sensory analysis indicated large differences in wine flavour properties, with closures which tended to result in the best retention of free SO2 having wine sensory scores for 'citrus' that were generally high whilst scores for the attributes 'developed'/'oxidised' were low. The situation was reversed for wine under closures that performed poorly in the retention of free SO2. It was found that below a critical level of free SO2 remaining in the wine, closures exhibited substantially higher 'oxidised' aroma. Whilst trichloroanisole-type (TCA) taint was a noticeable problem for some cork and technical cork closures, any plastic-type taint appeared not to be a problem with most synthetic closures.