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A Technical Guide for Wine Producers
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Alternative bottle closures and supplier techniques aimed at improvement
Ever since the 17th century, the combination of glass bottles and cork as packaging for wine has been associated with wine of good quality. This is not surprising considering the technical characteristics of cork, which has special properties as a natural closure. As a result of the natural origin of cork, however, it may result in heterogeneous quality. This may cause leakages from bottles and moreover, cause cork taint in wines.
Although cork taint has been a problem for many years, it was only towards the end of the twentieth century that chloroanisols (especially 2,4,6-trichloroanisol or TCA) were confirmed to be mostly responsible for the so-called corky character. This is caused by fungi resulting from chlorine compounds. Cork is not the only source of taint, however, since chlorophenols used as a preservative in wood may also be transferred to wine and cause a false corky character (1).
Not surprisingly the above-mentioned potential problems went hand in hand with growing interest in alternative closures. Screw caps, different kinds of synthetic cork and also combinations of synthetic and natural cork have been considered as alternatives.
In view of the potential impact of these problems, Australian researchers engaged in a comprehensive study of different closures on a 1999 Semillon in 1999. Fourteen different closures were investigated, one being a screw cap, two natural corks, two natural-synthetic combinations and nine synthetic closures. In some instances the research took as long as 20 months (2). The most important findings from the research were the following:
Taking into account the above problems, wine cellars have been increasingly inclined to use alternative bottle closures. The tradition of cork is no longer a good enough reason to persist using it as a bottle closure. Australian cellars are especially prone to using screw caps as alternative, being more cost-effective and to a certain extent, acceptable to consumers (3).
Seeing that chlorophenols were revealed to be the most important precursors of chloroanisols with specific fungi being responsible for the conversion thereof (4), it was obvious that research conducted by cork suppliers would have to focus on eliminating the precursors and the particular organisms in the cork manufacturing process, and also on preventing possible recontamination. Hence the development of various cork treatment processes. Amorim, the biggest cork producer in the world, developed the so-called ROSA process. This entails a controlled steam distillation process that is able to reduce the free TCA levels in cork by 80%. The French company Sabaté developed a supercritical carbon dioxide extraction process able to remove TCA from the cork raw material. Improved control over the raw material, improved boiling processes as well as ozone washing processes are other aspects that have been addressed (5). Ultracork uses ultrasound treatment to remove free TCA from corks and Juvenal uses the DELFIN microwave treatment to eliminate microbiological activities. The process entails the utilisation of electromagnetic waves to remove toxic compounds and reduce the micropopulation (4), (6).
For the time being, however, it remains uncertain whether cork does indeed play a role in the unforeseen potential oxidation of bottled wines, although cork suppliers are looking into the matter.
Meanwhile innovative ideas have also resulted in other alternative bottle closures. ZORK is a bottle closure that, although consisting of a single piece, actually has 3 components. It fits onto standard bottles, allows contact with limited amounts of oxygen, just like a natural cork, and also sounds like a cork when the bottle is opened (7).
VINOLOK is a reusable glass closure and was developed by ALCOA. Comparative evaluations with natural corks are currently under way at Stellenbosch University's Viticulture and Oenology Department.
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