An important outcome of the Australian Wine Research Institute’s research on wine closures is the recognition that when a wine is bottled under different closures, different wines begin to be created from that point onwards. Other workers have apparently expanded this concept to other bottling variables such as the filling height, the concentration of Free SO2 at bottling, and the mixture of gases in the headspace of bottles post filling. The ability to link such variables to wine development post bottling creates the possibility of reliably predicting, and therefore optimising, wine development in bottle. This would enable wine producers to consistently offer wines to the market in optimal condition. As understanding of these factors increases, ever-tighter specifications for both closures and bottles may be set in order to minimise variation in wine development between bottles. The gap between reliable closure performance and wine producers’ expectations of the manner in which closures need to perform, is smallest with manufactured closures. In particular, screwcaps have the proven ability to deliver the desired homogeneity. Technical corks, some synthetic closures, and novel closure technologies such as membrane barriers to oxygen and TCA for natural or synthetic corks, might all be able to deliver the tighter specifications demanded by wine producers, and the development of such technologies will inevitably continue. Understanding of the impact of the closure on wine development has been elucidated by the AWRI’s various closure trials. The original trial commenced in May 1999 with the bottling of a Semillon wine under 14 different closures. Results of testing conducted at 60 and 63 months post bottling for five closures (roll-on tamper evident ‘ROTE’ or ‘screwcap’ closures, Altec and One + One technical corks, and ‘reference 2’ and ‘reference 3’ natural wine corks) showed that the ROTE and the Altec closures continued to retain a significantly higher concentration of SO2 in the wine compared to the One + One and reference 2 cork closures, which in turn retained a significantly higher concentration of SO2 in the wine compared to the reference 3 cork closures. Higher SO2 concentration continued to show a strong negative correlation with optical density at 420 nanometers for all closures. Likewise, during sensory evaluation, ratings for overall fruit aroma and citrus aroma were strongly positively correlated with SO2 concentration, and were negatively correlated with ratings for oxidised. Ratings for struck flint and rubber aroma were also, to a lesser degree, positively correlated with SO2 concentration. In a second trial, a Semillon wine was bottled under screw caps with both a ‘high’ and a relatively ‘low’ concentration of SO2, and at two filling heights. Sensory evaluation of the wine conducted two years post bottling showed no relationship between increased SO2 concentration and ratings for H2S/cabbagey aroma, and an inverse relationship between increased SO2 concentration and ratings for struck flint/rubber aroma. However, it is considered possible that the elevated concentration of free SO2 in the ‘high SO2’ treatments (42 mg/L for the ‘high fill height’, and 39 mg/L for the ‘low fill height’ treatments respectively) might have interfered with the assessors’ ability to evaluate the wines. Nevertheless, these data, and those from the first trial, suggest no causal relationship between increasing SO2 concentrations and increasing ratings for ‘reductive’ characters during sensory evaluation. Additionally, in this second trial the varied ullage at the time of filling had no influence on ratings for flint/rubber and H2S/cabbagey during sensory evaluation conducted two years post bottling, at either SO2 concentration. In a third trial a Chardonnay wine was bottled with screwcaps, and a portion of the wine was also sealed in glass ampoules in the absence of oxygen. Four years post-filling, the wine sealed by both methods received the same rating for the attribute oxidised during sensory evaluation, but the wine sealed in ampoules was rated significantly higher for the attribute reduced. Wine under both treatments had retained a similar concentration of SO2. The currently available stocks of some of the closures examined, and, therefore, their performance, might differ from those available when these trials commenced. Similarly, the closures have been used to seal only the wine types defined under the conditions described, and care should, therefore, be exercised when relating the results reported here to other wine types, or to wines stored in less than industry best practice storage conditions. Full details of the wine, the bottling procedures and storage conditions are contained in the Australian Journal of Grape and Wine Research 7 (2), 62-105. Any reference to ‘Tage’ closures in this presentation or in the publications referred to, are references to closures manufactured by APM in the USA, and not by Novembal in Europe. The closures were obtained from the Australasian agent, Esvin Wine Resources. The AWRI takes no position on the rights of APM or Esvin to manufacture or sell closures under the name ‘Tage’.
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