The New Zealand Screwcap Initiative 

(This is a slightly modified version of a piece written for Harpers. Jamie Goode) 

To the casual observer, it must seem very strange indeed that the hottest topic in the world of wine – well, at least the one guaranteed to fill the letters page the fastest – is nothing to do with wine itself, but rather the packaging. Welcome to the wine bottle closure debate. In one corner we have the revolutionaries, the screwcap crusaders. In the other, the supporters of the poor old cork. These groups have been battling away in earnest for several years now, and currently the screwcap crusaders, preaching their message with evangelical zeal (an Australian jo urnalist called Tyson Stelzer has even written a book about screwcaps, and has followed this up with a tract to be handed out to consumers), seem to be winning the battle.

With its Screwcap Initiative, and the recent inaugural Screwcap Symposium held in Blenheim, New Zealand is now leading the way in advocating the widespread use of screwcaps as an alternative to corks. It could well be that in 30 years time people will in retrospect consider that New Zealand’s greatest contribution to the world of wine is not its remarkable Sauvignon Blancs, or even its supple Pinot Noirs, but instead the way it led the wine world to shift from variable, taint-prone corks to embrace screwcaps. The goal of this feature is to review the rise of the screwcap as cork’s leading contender, and to try to present a balanced assessment of the key scientific issues at the heart of the closure debate. 

The closure debate is a crucial one, and it seems to be entering an important phase. The rhetoric is cooling down a little, and new data are emerging that are informing discussions which previously relied on merely anecdotal data and theorising. The cork industry has begun to address the problem of taint with actions, rather than just words, and at least some of the larger players are now making serious efforts to reduce taint levels in a way they simply weren’t a few years ago. On the face of it, it’s a simple problem with a simple solution: cork taints roughly 5% of the wines it comes in contact with, and there are other problems associated with its natural variability, such as random oxidation and wildly varying oxygen transmission that leads to uneven ageing. Screwcaps are inert, cheap and provide a good seal, so why don’t winemakers switch to them now? In reality, the situation is rather more complex.

Introducing the screwcap
Screwcaps as an alternative to cork for bottling wine were born in 1959, when French company La Bouchage Mecanique introduced the Stelcap-vin as an alternative to cork. Their Stelcap closure had already proved successful for a range of spirits and liqueurs. The rights to manufacture this closure were acquired by Australian Consolidated Industries Ltd (ACI) in 1970. It was renamed Stelvin for the Australian market and trials at the ACI laboratories took place. The results were reported for the first time in 1976 in a paper in The Australian Grapegrower and Winemaker. Four closures (three screwcaps with different wadding materials and a cork for comparison) were tested on six wines (three white and three red). The conclusions were that screwcaps were ideal for sealing wine bottles but only if they had the right wadding material and that satisfactory seal was obtained between bottle and cap. Interestingly, the best-performing Stelvin closure at the time had agglomerated cork as part of the wadding, although this wasn’t in contact with the wine. This trial continued through to 1979. Although there was an industry push to move to screwcaps, this lost momentum, partially through fears about consumer acceptance, and also because awareness of the shortcomings of cork, particularly its high taint rate, were not as widespread at the time.  

Jeffrey Grossett, one of the winemakers involved, estimates that from this humble beginning, during the 2004 vintage 200 million wine bottles will be sealed with screwcaps in Australia, roughly 10% of the entire Australian production. The Clare initiative started the ball moving, and prompted the New Zealand winemakers to form the NZ Screwcap Initiative a year later (see box). “We were inspired and encouraged by the success of the Clare Valley Riesling move to screwcaps in 2000”, reports one of the founder members, Michael Brajkovich MW of New Zealand’s Kumeu River Wines, “and like them we realized that we could achieve much more with a combined effort than we could ever do individually.” The situation in New Zealand is such that from an estimated 1% of wines sealed by screwcaps in 2001, bottles sealed with this closure are now in the ma jo rity. “There are over 400 wineries in New Zealand, and although about 70% of the wine is now being sealed with screwcaps, I would doubt if that figure would be anywhere near correct in terms of the number of winemakers using screwcaps”, says Brajkovich. “There is still a sizeable group who have remained loyal to cork. This includes some who seem to be annoyed at the approach taken by the Screwcap Initiative in publicizing the benefits of screwcap usage. In extolling these benefits we necessarily have had to mention the many shortcomings of cork, and this has placed some pressure on those who continue to use cork to defend their position.”

Around the same time, an important study on closures was published in 2001 by scientists from the Australian Wine Research Institute. This large, ongoing study compared the performance of a range of closures, and the results from 20 months into the trial allowed three important conclusions to be drawn. First, screwcaps provide a seal that is better than that of cork. Second, that cork shows a wide variation in oxygen transfer characteristics. Third, that the synthetic corks included in the trial have the highest gas permeability and are only suitable for wines destined for early drinking (for the sake of fairness, I should add that newer, better synthetics are now available). The debate had shifted onto new ground. Now, the key question surrounds whether a tighter seal than that provided by cork is desirable, and whether red wine in particular needs the very small amount of oxygen transmission permitted by the average cork for successful ageing to occur. And does this tighter seal lead to much-discussed problems with reduction?

Screwcaps for all?
Michael Brajkovich is one of the leading advocates of screwcaps, and as an early adopter, he moved the entire production of his Kumeu River Wines to this closure in 2001. For two years he was chairman of the NZ Screwcap Wine Seal Initiative, and is still on the committee. I asked him whether he envisaged a situation where screwcaps will become the closure-of-choice for all wine types? Does cork have a future at all? “Without a crystal ball, this is very difficult to predict,” says Brajkovich. ”There are a number of new alternative closures and technical corks coming on to the market that have some very good attributes, (especially when compared to natural cork), and which will take up a significant market share in addition to screwcaps and traditional corks. From what I have seen so far, however, the screwcap is still my choice as being technically the best.” With regards to potential problems with the tightness of the seal provided by screwcaps, and their suitability for ageing red wines, Brajkovich had this to say. “We can talk about oxidation/reduction, bottle maturation, oxygen transmission rates and redox potentials as much as we like, but the fact remains that many people will not be convinced of the efficacy of screwcaps for red wines that age until they see the evidence for themselves in terms of an old wine. We have certainly seen that evidence in aged Riesling from Australia,” he continued, “but the red wines are few and far between. Some Australian companies have some long term red trials down now, but it will take time for the results to become clear. We have also heard about some older examples from France, including a 1966 Mercurey that convinced Boisset to try screwcaps with some quality red and white Burgundy appellations. As Tyson Stelzer pointed out at the Screwcap Symposium, all it takes is one really good example of an aged red wine under screwcap to show that it is possible.”

This is a critical issue. How come we don’t have good data on whether oxygen transfer is needed for successful ageing of red wines, or any wine, for that matter? The answer is twofold. Firstly, it’s very difficult to measure. We are talking about incredibly tiny amounts of gas transmission, and the machinery used to measure this, the Mocon Ox-Tran machine, takes a long time and is expensive. Secondly, and more importantly, wine ageing is a complicated chemical process that is poorly understood. It’s not possible to determine the effect of tiny amounts of extraneous oxygen over many decades other than by just seeing what happens with a real wine. It’s a frustrating situation. Now that it’s possible to dial up or down the amount of oxygen transfer that a screwcap allows by toying with the wadding composition, if we knew that the oxygen transfer level allowed by an average cork were ideal for red wine development, then we could produce screwcaps that sealed to a similar degree, but which would offer much greater consistency and the absence of taint. “I suspect that it will turn out that a very low oxygen transmission rate, similar to that with a normal screwcap, will be the most desirable for bottle ageing”, says Brajkovich. “This would support the notion that bottle maturation is a chemically reductive process that takes place despite the ingress of oxygen, not because of it.”

Other problems
Longevity of screwcaps doesn’t seem to be a problem for wine ageing. “Screwcaps are ‘guaranteed’ to last at least 10 years if the bottle and application machinery are correct. In practice we have seen screwcaps last for 25–30 years without problem,” says Brajkovich. He adds, “Given that corks should really be replaced after about 30 years, the use of screwcaps for long term red wine ageing is definitely within the normal performance specifications of other closures, and time will tell just how good they are at performing the jo b.” He thinks that screwcaps will turn out to be ideal for red wines as well as whites. 

The reduction issue is still seen as a problem, although screwcap advocates claim that this is more a problem with the winemaking than the closure. For those baffled by the term ‘reduction’, in this context it refers to a group of volatile sulphur compounds that can emerge as wine aroma faults when there is an absence of oxygen, specifically in this case aromas described as ‘struck flint’ or ‘rubbery’, thought to derive from disulphides. In the limited amount of published work on this issue it seems that reduced characters aren’t unique to screwcaps, but that these problems can be alleviated by careful winemaking. It may take time to get this right, and with the increasing number of screwcapped bottles being sold it is likely that screwcaps will come under intense scrutiny over the next few years. With this in mind, winemakers need to be careful to choose only good quality caps to work with, and to use them properly – a number of different manufacturers are offering them, and it is likely that they won’t all be of the same quality.

The future
So what is the future of the Screwcap Initiative? “We acknowledge that although acceptance of wine sealed with screwcap is just about complete in Australia and New Zealand, this is certainly not the case internationally”, says Brajkovich. “As indicated at the Screwcap Symposium, part of that direction will be the formation of an international group to carry on the efforts of the initiative in a more global setting. We would like to think that anyone wishing to use such a closure in a more traditional wine producing country would not be disadvantaged by negative perceptions of the screwcap that are based on erroneous information. In some parts of the world there is much work needed to be done to change these perceptions.”

I’ll close with a problem that has bugged me for a while. Cork taint isn’t new. Despite the often quoted assertion that chloranisole contamination of corks is a consequence of chlorine-containing bleaches that used to be employed in cork processing, it’s likely that taint is endemic to cork. Because of the structure of cork bark, which is riddled with tiny pores (lenticels) that can harbour chloranisole-producing microbes, cork is tainted to a degree even while it is still on the tree. It may never be possible to eradicate TCA and other taint causing compounds from cork, although some progress in reducing the levels from the current high rate could be expected by improvements in quality control and modifying the riskier processing steps. This raises the question: if cork taint has always been with us, then why has it been tolerated for so long? It’s hard to give a definitive answer. It may be that taint is less evident against the backdrop of ‘old world’ wine styles, which generally have less emphasis on primary fruit character. It may also be the case that consumer acceptance of alternative closures is so poor that switching to screwcaps would be commercially disastrous. A slightly dangerous response is that in old world wine countries there is less emphasis on product quality and greater tolerance of what could be considered wine faults by consumers and even the wine trade. The fact that the wine industry trades heavily on tradition may imbue it with a degree of inertia, and thus a significant change such as changing closure type is perceived as more problematic than a 5% taint rate. In addition, in the old world wine is marketed not just on the basis of product quality. Consumers are frequently being sold a slice of culture, a piece of history, a story to be told with each bottle that they buy. Could it be that the wine quality is just an element in this product? And if the cork is an important component of this package, do winemakers feel they are free to replace it? 

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