Stoppers – cork, plastic or screwcap? Australia tells us at last


18 August 2016  Just look at when the article below was published – almost exactly FIFTEEN YEARS AGO! And how much has changed in the world of stoppers, or closures, since then. We have seen a massive swing to screwcaps, particularly but by no means exclusively in Australia and New Zealand (although some of the new-wave Australian producers are now using natural cork as a point of difference). And there has been enormous progress in the amount of research and development devoted to each sort of stopper. The cork industry has – not before time – dramatically pulled up its socks and can offer an array of different products, some of them with hugely reduced and sometimes minimal risk of cork taint, as well as individually tested corks. And screwcaps have become very much more common, having been associated initially with problems of reduction but now available in a range of different oxygen transmission rates thanks to our greater understanding of TPO (a term that didn't even exist when this article was written). The quality of synthetic closures has also come on in leaps and bounds since the publication of this article. A carbon-neutral synthetic cork made from sugar cane is even available nowadays. 

We are publishing the article below in our Throwback Thursday series just to show you how much more we know today and how the world of wine stoppers has evolved. 

20 August 2001 Everyone and his dog has a view on this by now. Mine is still that I find plastic corks unattractive, difficult to re-insert, silly (because they are ersatz in every way) and low-scoring on ecological grounds. Natural corks offer the same sort of comfort and aesthetic appeal as anything wholesome, but there is an inconveniently high incidence of off-smells (a bit like open sandals really). Screwcaps do the job of keeping out the oxygen that prematurely ages wine but don't exactly have visual appeal, even if at long last the wine trade is becoming braver about using them for white wines.

There are many interested parties in this debate – not least the rural economy of Portugal as well as the manufacturers and suppliers of stoppers. The biggest of all of these, the Portuguese natural cork supplier Amorim, is spending a fortune on flying wine writers and authorities around the world, sponsoring conferences and other worthy winey activities, in order to convince us that they are good guys par excellence. They are also, at long last, devoting sufficient resources to the R & D needed to combat the problem of cork taint.

Objective information about the performance of different wine bottle stoppers has been thin on the ground up to now but the good old Australian Wine Research Institute, the most respected in the English-speaking world and grudgingly admired even by the French, has just published its first findings on the subject, which are rather more detailed than a previous Bordeaux study by Chatonnet et al.

They chose a relatively full-bodied white wine, an Australian Semillon, and bottled it in late May 1999 using 14 different stoppers, or 'closures' as they are known in the wine business (the word having a different resonance in the world of psychotherapy). Of the 14, two were different grades of natural cork, two were 'technical corks' (natural cork with a synthetic component: Altec and Amorim's Twintop), nine were plastic of various sorts and provenances and one screwcap.

This experiment will continue but already the AWRI has issued the following conclusions:

While many of the plastic and technical corks were fine for six to 12 months' storage, most of them start to let in oxidising oxygen after this. The British Betacorque plastic cork performed worst in this respect.

The screwcap is by far the most effective seal against oxygen. If you want to prevent a wine from going brown and losing freshness, a screwcap is best (an advantage for fruity whites, not necessarily for all reds).

However, after 18 months, the wine under the screwcap developed a rubbery smell. A number of those wines under natural corks and the wine bottled under the Franco-American Altec technical cork were marred by mouldy TCA. The wine stoppered by the Betacorque developed a plastic-like aroma.

No single stopper was deemed perfect by the scientists. The problem with natural cork remains – too high an incidence of cork taint.

But then we knew that, didn't we?

Is it really beyond the wit of designing man to come up with a better alternative stopper?

3 September 2001

I had this particularly thoughtful and well-informed feedback from Michael Brajkovich, New Zealand's first Master of Wine and force behind the admirable Kumeu River winery.

'Our collective opinion at Kumeu River has been arrived at after a long period of reading, trialling and tasting. The conclusion we have come to is that screwcaps are the way to go, and we have consequently decided to start closing all of our wines with Stelvin from Pechiney.

I think that the research from the AWRI has given a very good lead in this direction, but is only an adjunct to the tasting and testing we have done ourselves over the past few years.

Just a few comments from our point of view on various aspects of the debate:

    Synthetic corks do not work for us. Apart from the obvious oxidation after 6 months, we always detect a distinct "plastic" aroma with these wines.

    The rubbery smell detected under the screwcap in the AWRI trial is most likely to have come from further chemical reduction of traces of hydrogen sulphide remaining in the wine at bottling. In no other wine sealed with a screwcap (from 2 to 20 years old) have we seen any such character. The oxidative nature of the other closures in the AWRI trial meant that the rubber character did not develop with them.

    All the reading I have done shows that the real cause of bottle age in wine is the complex of slow, reductive reactions that take place in the absence of oxygen. These occur more favourably with a screwcap.

    Studies have shown remarkable variability in the gas permeability of corks, in the order of 1,000 times difference. If oxygen was so important in bottle age, we would expect to see even more variability in aged wines than we currently do. My suspicion is that the best ageing conditions occur when gas exchange is minimised, and the reactions are predominantly reductive. These favourable conditions are perfectly uniform with screwcaps.

    The problems with natural cork are not just confined to cork taint, but also include random oxidation and premature maturation. Together these cause problems that we are only just starting to appreciate the magnitude of, and the situation is totally unacceptable. Our solution is to totally abandon this flawed system, and move to a proven, much more successful alternative.

    The tasting in Marlborough last week at the launch of the Screwcap Initiative showed clearly the ability of Riesling to age beautifully with screwcaps. We had six vintages of Bethany Eden Valley Riesling (1995-2000), plus some lovely old aged Pewsey Vale Riesling from Yalumba. From this evidence I am sure the same will be true for other white varieties such as Chardonnay, and it is also highly likely that the same applies for red wines. We are so convinced of this that we have decided to make the change to Stelvin for all our wines: white and red.

    The visual appeal of screwcaps has long been considered n problem, but the manufacturers are now doing a much better job in terms of colours and graphics to improve things. We were astounded at how good our new caps looked when they arrived a few weeks ago and we first tried them out.

    We bottled our 2001 Kumeu River Pinot Gris only 2 weeks ago, with some bottles sealed with cork for comparison purposes. Already we are seeing a big difference between the two, with the cork giving a distinctive "cork" taste (but not taint) and the Stelvin being completely clean and fresh.

On that evidence one would not want to look at a cork ever again. Long may the debate continue, because changing ingrained attitudes will only come about from informed discussion.'