Better matured with screw cap

We should all know this by now. Numerous studies by renowned research institutes from all over the world have been proving for years and decades that wines benefit just as much from a screw cap as they do from a natural cork, provided the latter is of good quality – and unfortunately this is far too often not the case. Cork taint, tannin ingress, oxidation, runners, crumbling material, limited shelf life – the list of shortcomings of natural corks is long. Nevertheless, thanks to a deep emotional bond between winemakers and wine drinkers that cannot be explained rationally, the traditional stopper is still usually the first choice, especially for high-quality wines. While cork has a dubious image as a natural product, the screw cap is still plagued by prejudices that date back to the pioneering days when many seals still contained plasticisers such as bisphenol-A. In the meantime, however, sealing discs made from sensory-neutral and harmless Saran tin have long since established themselves.

Many advocates of natural corks point out that the wine can “breathe” better under a natural cork and therefore matures more attractively. But in many cases the oxidation caused by a leaking natural cork leads to the premature destruction of the contents of the bottle. Whether the wine was matured reductively or oxidatively is irrelevant.

Measurements show that the range of oxygen exchange with screw caps is far lower than with natural corks. However, the value ranges overlap. An ideal natural cork therefore hardly differs from a screw cap in terms of gas tightness.

The experiments at the Wädenswil Winegrowing Centre in the Swiss canton of Zurich lasted over 20 years. Bottles with various screw caps and natural corks were filled from a tank and repeatedly opened and tested. The results were clear. While the natural cork showed ever greater differences with increasing age, the Wädenswil researchers confirmed that the wine with the screw cap shows the better maturity.

Other research institutes came to the same conclusion. In the New World, the screw cap has therefore long since established itself in the premium wine segment.

In order to understand the results of the research institutes, of course without claiming to be representative, we taste a 2012 Serrig Schloss Saarsteiner Riesling Kabinett from the Saar, which winemaker Christian Ebert filled eleven years ago, partly with natural cork and partly with a screw cap. We open a bottle from each of the two bottling series around an hour before our blind tasting. Two of us taste, using the triangle test. In each of five flights, every taster has the screw cap and the natural cork in front of him twice as deviator, and once all samples are identical (whether screw cap or natural cork). Of course, we have no information about the existence or nature of the deviant at the time of our tests.

We were lucky with the natural cork this time. The triangle tests showed no sensory differences. The deviant was only recognised (or guessed) in a total of three of ten cases and correctly assigned to the closure type in only two cases. The identical samples were not recognised in either case. Seen in this light, there would actually be nothing to speak against the natural cork, would not have been there the recurring defects. However, as none of the independent studies or our tasting revealed that the natural cork was more mature, the screw cap emerged from the comparison as the clear winner on points. This is by no means surprising, and in fact we have all known this for a long time.