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

Abstract

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.

Spoilage of bottled red wine by acetic acid bacteria

“…However, various studies with natural cork implicate variation in their oxygen permeation characteristics as measured by the rate of oxidation of wine constituents, such as ascorbic acid, sulphur dioxide and phenolics (Waters et al 1996;Caloghiris et al 1997;Godden et al 2001;Jung and Zürn 2001), and it has been estimated that over a year, several millilitres of oxygen could enter a bottle via this route (Ribéreau-Gayon et al 1976;Casey 1992). There is a growing body of evidence to suggest that vertical storage of bottles, where the wine is not in contact with the cork closure, may decrease the ability of the cork to exclude air (G. Skouroumounis and E.J.…”

“…Numbers refer to numerical similarities storage time is not strong. However, the second hypothesis only depends on oxygen being the limiting factor for bacterial growth as well as the natural variation in oxygen permeability characteristics of natural cork closures that can be inferred from recent studies (Godden et al 2001). In this hypothesis, bacteria entrapped in a film of wine, which forms up the side of the neck of the bottle, under the action of a trace amount of 'new' oxygen provided by only those cork closures having a higher permeability to oxygen, would modify their immediate environment by a combination of metabolic and chemical oxidative reactions.…”

“…That oxygen entering the bottle via the cork closure was the trigger for visible spoilage was shown by the fact that ROTE sealed bottles did not spoil. All studies published to date have demonstrated the reduced rate of wine oxidation in bottles closed with the ROTE closure (Godden et al 2001).…”

“…These include the poor performance of bottle closures that may allow the ingress of oxygen (Zurn et al 1995;Waters et al 1996;Caloghiris et al 1997) and the manner in which the bottles are positioned during transport and storage (Godden et al 2001). Generally, bottles are stored on their sides with the wine in contact with the cork closure, but there has been a recent trend to store bottles in an upright (vertical) position during transportation, leaving a headspace of gas in the neck of the bottle, between the surface of the wine and the cork closure.…”

Cosorption of Sulfur Dioxide and Water on Cork

“…The mass of SO 2 sorbed by a standard cork stopper weighing ~3 g would be equal to 0.3 mg, representing ~1.6% of the free SO 2 in a bottle of wine. Consequently, the decrease in the SO 2 content observed by several authors (Keenan et al 1999, Brajkovich et al 2005, Godden et al 2001, 2005, Skouroumounis et al 2005, Kwiatkowski et al 2007) during aging of wine stored in bottle cannot be attributed to its sorption on cork. For some of these studies, the sharp decrease in SO 2 concentration in wine during the first three months of storage can be attributed to the presence of oxygen in the bottle headspace at bottling (if air has not been withdrawn) and its subsequent dissolution in wine and reaction with SO 2 .…”