Over the last year there has been intensive publicity relating to the virtues of Stelvin or ROTE (screw-cap) type bottle closures and comparing these to corks. A number of winemakers have lent their weight to the campaign for changing to Stelvins, pointing to the problem of 'corked' wines (presently -in 2002- thought to be 6-10% depending on the corks) explaining that it is their desire to give the consumer a better deal which has led them to this. [It is worth stressing that no-one is criticising the job done by sound corks.] Such comments built to almost a religious fervour, and following all this the continual queries as to ‘where do I stand on this matter?' started to assume the mantle of ‘most boring question of the year' for me. However the latter description does not do justice to the importance of the central issue, just as the original comments by the winemakers making the change, probably overstated the problem: after all, any reputable winery can be presumed to have a policy of replacing or refunding bottles which have been tainted in this way (see our 'General Notes' in our Spring Release brochure).
There have been a number of trials completed with Stelvins but these seem to be predominately for Riesling or Riesling styles in what appear to be relatively short term wines. It has been found that the screw-cap closures can provide very effective seals, limiting the access of oxygen to well below that for normal corks, allowing shorter term wines to look fresh for much longer than they might otherwise. These results are widely accepted (with caveats), but the concern voiced by Europeans (and also in the scientific literature) is that the risk of cork taint is then replaced by the possibility of a ‘reductive taint' if the wine has a good extract and is kept more than a couple of years.* My personal view is that top tier wines with high extract (which will therefore have high levels of natural antioxidants), may be at the greatest risk. These same ‘antioxidants' provide structure for young fine wine and it appears possible that it might become desirable for fine wines to be made differently to reduce this perceived structure if they are going to be stored in screw-cap bottles under these very different conditions. It is worth also noting that corked characters in wine are thought to arise mainly from the traditional rinsing and conditioning procedures during the cork manufacture, which are not very effective in removing the microflora responsible for production of this flavour taint, and which do not dry efficiently enough to prevent its further multiplication. However, by June 2002 a revolutionary rinsing and conditioning machine will be in use across the cork industry in Portugal and this new system is expected to bring down the incidence of taint to about 2%. Time will tell all.**
The screw-cap solution to cork taint is not the only alternative that has been offered the industry over the last 20 years. A variety of synthetic corks have been embraced at various times. Some of these were later discarded for introducing their own peculiar taints into the wine, others have been very poor barriers to oxygen - causing the wine to die prematurely, most are considered to lack the long-term elasticity of natural corks and therefore may present problems for long term cellaring, but according to tests some others have been found to perform well at least in the first few years insofar as they do not offer taints, and although their barrier to oxygen over this period is not quite as good as cork, it is probably acceptable. To my knowledge, no synthetic cork has yet gained wide acceptance in the quality end of the market. There are other groups of closures which include ‘Technical Corks - also trialled in Australia - involving layers of cork glued across the end of a suitable cork base. The studies done on these are not encouraging on the grounds of the higher level of cork taint reported. Yet another solution to the ‘problem' is likely to start trialling in New Zealand this year. This is a cork which has a synthetic polymer layer at the end of the cork which is in contact with the wine. When the cork is inserted, the synthetic polymer or disc is compressed onto the sides of the bottle and excludes any direct contact between the wine and the cork. Trials on the brand being introduced into NZ seem to demonstrate that this layer is very effective in stopping migration of taints from the cork to the wine and preventing the occurrence of ‘leakers'. The exclusion of air for this closure is inevitably at least as good as ordinary corks, and for the version being introduced to New Zealand is claimed to be very similar. Trials of two proprietary versions of this closure in Australia found they limited the access of air to the wine to somewhere between that for corks and Rote closures and it therefore remains a possibility that if reductive characters are eventually found with some wine-types stored under Rote closures there is a lesser possibility that they might also occur with these. If these closures prove not to exhibit this particular disadvantage, they seem to offer an exciting prospect - having none of the disadvantages of synthetic corks and other closures plus all of the attractiveness of real corks.
In the meantime, Dry River will plod along doing the ‘traditional thing' and can be expected to change from old-fashioned corks when the majority of our clients want a change to a closure which has consistently proven to be better than the alternatives for a range of top quality wines, for a minimum of seven years.
* In his comments on the Air New Zealand Wine Awards, the Chairman of Judges noted that "Some obvious concerns were: too many wines were showing sulphides that were under screw cap. Something to watch" The technical problem for these winemakers is that the problem need not arise from poor practices which have allowed wine with some hydrgen sulphide to be botlled, as has been claimed by the media. A wine which tastes and smells perfect to most people can still generate problems and until winemakers master this subtle technical problem a much greater potential risk will remain than for the traditional closure. It is a soluble problem.
However this is all is quite apart from the fundamental aethetic issue of whether a wine stored under screw cap presents as attractively as that from under a cork which has allowed small amounts of oxygen to participate in the process of maturation.
**The technical improvements promised for 2002 have indeed eventuated. This winery does Quality Assurance sampling and testing of all its cork batches before use and we would reject any cork batches which show cork taint incidence around 3% or more. We would concur with the suppliers comments that the taint level (from our supplier at least) is generally less than 2%. Additional to this are further technical advances coming on stream. One is the 'Rosa' wash which includes ozone and steam rinsing for twin top corks and which is now in commercial use. This process will soon be used for traditional natural corks and it is expected to reduce taint to less than 1%. A competing technology is the Sabaté process, christened Diamond. This utilises a 'supercritical extraction' (ie. liquid) carbon dioxide in the manufacture of reconstituted corks and when this technology is aplied to natural corks I would hope that the results will be at least as good as for the 'Rosa' process.