The Australian Wine Research Institute has added facts to the debate over bottle closures, which seem sure to heighten the cork versus synthetics controversy.

"No one closure test in this study could be considered entirely suitable by all criteria assessed for the long term storage of wine," it reported this week.

The study in question began with the bottling under controlled conditions in May, 1999 of a Semillon (white) wine. The Institute - a national, independent body affiliated to the University of Adelaide - tested 14 different closures, a screw cap, two grades of conventional cork, two types of technical cork (natural cork with a synthetic component) and nine manufactured from synthetic polymer material.

The first results of the trial are now published. The study is continuing with enough wine for up to ten years of testing. "It is apparent from the results to date that many of the closures trialed are suited to short term - approximately eight to 12 months - storage of wine but for longer time periods there is doubt over particular closures' abilities to act as an adequate seal with consequent effects on sulphur dioxide levels, browning and an oxidised aroma," it was concluded.

Screw cap sealed wine retained the greatest concentration of sulphur dioxide and had the slowest browning rate. With the others the relative loss was most evident in the synthetic closures, intermediate in the conventional corks and least evident with the technical corks.

The suplhur dioxide concentration was a strong predictor of future browning. After a year wine in bottles with the lowest sulphur dioxide concentration were rated sufficiently high in oxidised aroma to consider them markedly lower in quality.

While TCA taint was a problem for some corks and technical corks, any plastic type taint appeared not to be a problem with most synthetics. But after 18 months a rubber like aroma developed with the screw cap closure.

The Institute study said the synthetics seemed least consumer friendly in terms of the force and energy required to extract them and ease of manual reinsertion into the bottleneck.

These full first findings are published in the Institute's Australian Journal Of Grape and Wine Research.

Wines & Spirits in Australia