Michael Fridjhon: Is the closure war coming to an end?

By , 25 April 2018



The debate around closures has been part of the world of wine for several decades, and like most matters where belief carries more weight than the facts, it has acquired the intensity of religious dogma. There are several obvious reasons for this: from the moment an alternative to cork presented itself, it was in the interests of the cork industry to vilify “the enemy.” This meant that stelvin was labelled “cheap and nasty” while those in the screw-cap business had to emphasise cork’s Achilles heels: taint and oxidation. Cork in returned responded by claiming that oxidation was good (“screw-caps ’cause’ reduction”) and so the blame game has continued.

There has been a sense that any gains made by the one side will necessary be at the expense of the other – which in fact is a long way from the reality. The cork merchants boast about how strong their sales continue to be at exactly the same time as the screw-cap industry releases figures showing how many billions of units are sold every year. The market has grown, the products (on both sides of the great divide) have improved vastly and it really should be a case of “live and let live.” Only it isn’t.

The battle lines are still in place, the acrimony remains evident, and it’s increasingly difficult to know how much the situation is being fuelled by the industries themselves, or by those who are their acolytes. Accordingly it seemed worthwhile to look at the basic facts of the matter – partly with a view to de-politicising the debate, partly because consumers and producers will both benefit from a less hostile environment.

No one seriously questions the vast improvement in cork quality over the past decade. The era of 10% cork taint at a tasting are long past. I was reminded of this recently, at the annual wine judging academy, where the flights of the older (international) wines were compromised (as they are every year) by the cork quality of that era. Comfortably 10% of the samples were tainted. It was nothing short of a miracle that the 6 bottle vertical of Chateau Gruaud Larose (from 2005 back to 1966) emerged unscathed. In previous years the five decade tasting which wraps up that segment of the Academy has always had at least one – sometimes two – compromised examples. By the same token, most of the younger flights proceeded taint-free. At a guess I would say that the level of contamination was around 2% (and it’s not impossible that some of this may be cellar – rather than closure – related). You might argue that this is still unacceptable (you wouldn’t fly on an airline with a 98% safety record) but the improvement is real.

There’s still an issue of reduction with stelvin but this remains a winemaking/bottling problem rather than a screw-cap supplier issue. If a winemaker doesn’t understand that wines need to be prepared differently for bottling under stelvin rather than under cork, you can hardly blame the party responsible for supplying the closure. However, one of the issues that this raises is to what extent problems associated with cork have also been winemaker/bottling problems, rather than intrinsics related to the closure. Cork has been excoriated both for taint and for random bottle oxidation. It’s certainly true that in a very arbitrary way some corks are more permeable than others, leading both to fluid loss, but also to excessive oxygen ingress. Where we are now picking up premature oxidation on screw-cap closed wines it is safe to assume that the cause of this fault is (generally) not the closure, but technically incompetent pre-bottling preparation and/or poor bottling hygiene. De Grendel’s Charles Hopkins has conducted considerable research on the safe levels of dissolved oxygen in wines prior to bottling and it is clear that far too many winemakers ignore the importance of this measurement. Many are also negligent when it comes to supervising the mobile bottling companies who undertake their on-site bottling.

On both sides there have also been great technological advances: guaranteed taint-free corks are now available (admittedly at a considerable premium). You might argue that guaranteeing your corks taint-free is a little like a break-lining supplier guaranteeing that the brakes work – it’s what they’re supposed to be anyway. However, this now imposes a more serious onus on producers of ultra-premium wines to ensure that they (and through them all their customers – rather than arbitrary and unfortunate individual consumers) bear the cost of this final stage of wine quality. Diam agglomerates, found almost everywhere, are now widely used and are virtually taint free. Not all composite corks are made to this spec: Diam is the market leader, but not the only player in the taint-free agglomerate game. On the screwcap side there are linings offering varying degrees of permeability, ensuring a controlled degree of evolution for those wines which are expected to mature in bottle.

What has come from the almost boundless closure warfare of the past two decades is a significant reduction in consumer disappointment based on factors largely beyond the winemaker’s control. In fact, now more than ever, the responsibility has been shifted back to the producer who can choose the type of closure and then the appropriate risk of taint, reduction/oxidation. No longer can a winemaker anywhere in the world shrug his/her shoulders and look helpless when punters complain about an unsatisfactory bottle: either the cellar was dirty, the wrong closure was selected, the wrong bottling protocols were applied, or the cheapest solution chosen. Whatever the cause, consumers can vote with their wallets – which is the best chance we have of keeping the closure suppliers honest.

  • Michael Fridjhon has over thirty-five years’ experience in the liquor industry. He is founder of Winewizard.co.za and holds various positions including: Visiting Professor of Wine Business at the University of Cape Town; founder and director of WineX – the largest consumer wine show in the Southern Hemisphere and chairman of The Old Mutual Trophy Wine Show.


8 comment(s)

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    Vasileios Sakalis | 7 February 2021

    I’d like to inform you that concerning the issue with wines which develop undesirable aromas under anaerobic –no oxygen– conditions, Meyer Seals in Germany has developed the new generation of liners for wine screw caps, ALKOvin™ active. The liner offers protection against Oxidative and Reductive ageing! Through an “active” reduces and prevents the formation of Volatile Sulphur Compounds (VSCs), responsible for post bottling off-flavours whilst does not influence the typical varietal aromas. Moreover the ALKOvin™ active, which has been tested by the “Australian Wine Research Institute”, offers excellent oxygen barrier performance (OTR ≈ 0.0 mg O2/year) and it is free of PVDC and PVC! For further information or samples, please contact Meyer Seals (+49 176 1280 1832) or your closures supplier.

    Ryan | 5 May 2018

    What’s the opinion of metal bottle cap closures like Luddite uses on their Saboteur? Very tasty wine and easy to pop off!

    Le Penseur | 4 May 2018

    Dr. Waterhouse is a Chemist and Professor of Enology at UC Davis who studies phenolic compounds and how they effect wine taste and human health.

    Corks Seal a Wine’s Fate:
    Aging Wine in Natural vs. Synthetic Closures
    Most foods are best as fresh as possible. I remember picking peaches at my grandfather’s ranch in Northern California and eating them on the spot. What a taste! But the exceptions to this rule are the many wines that actually need some aging to taste their best. Winemakers know this, and work to control the aging process including decisions they make about how to bottle up their product.

    Aging and oxygen
    One aspect of aging has to do with the reaction of fruit acids with the alcohol. This process reduces sourness in the wine, but it’s really only important for very tart wines, the ones coming from cold climates.

    The complex oxidation process is the second aspect of aging. When oxygen interacts with a wine, it produces many changes – ultimately yielding an oxidized wine that has a nutty aroma. This is a desired taste for sherry styles, but quickly compromises the aromas in fresh white wines.

    However the oxidation process provides benefits along the way to that unwanted endpoint. Many wines develop undesirable aromas under anaerobic –no oxygen– conditions; a small amount of oxygen will eliminate those trace thiol compounds responsible for the aroma of rotten eggs or burnt rubber. Oxidation products also react with the red anthocyanin molecules from the grapes to create stable pigments in red wine.

    The way a bottle is sealed will directly affect how much oxygen passes into the wine each year. That will directly affect the aging trajectory and determine when that wine will be at its “best.”

    Stick a cork in it?
    Glass is a hermetic material, meaning zero oxygen can pass through it. But all wine bottle closures admit at least a smidgen of oxygen. The actual amount is the key to a closure’s performance. A typical cork will let in about one milligram of oxygen per year. This sounds like a tiny bit, but after two or three years, the cumulative amount can be enough to break down the sulfites that winemakers add to protect the wine from oxidation.

    There are three major closure options available: natural cork and technical cork, its low budget brother made of cork particles, the screw cap and synthetic corks. Natural cork closures appeared about 250 years ago, displacing the oiled rags and wooden plugs that had previously been used to seal bottles. It created the possibility of aging wine. Until 20 years ago natural corks were pretty much the only option for quality wine. It’s produced from the bark of the tree, and harvested every seven years throughout the life of a cork oak tree, Quercus suber. The cork cylinder is cut from the outside to the inside of the bark.

    A small fraction of corks, 1–2% today, end up tainting the wine with a moldy smelling substance, trichloroanisole (TCA). This TCA is created via a series of chemical reactions in the bottle: chlorine from the environment reacts with the natural lignin molecules in the woody cork to make trichlorophenol, which is in turn methylated by mold. TCA has one of the most potent aromas in the world – some people can smell as little as 2 parts per trillion in wine. So, in every eight cases of wine, one or two bottles will smell like wet cardboard or simply not taste their best. This is why restaurants let you taste the wine before pouring – to let you judge if the wine is tainted. A 1% failure rate seems high in today’s world.

    Plastic fantastic?
    Synthetic corks are made from polyethylene, the same stuff as milk bottles and plastic pipes. After years of research and development, these corks now perform nearly the same as the natural version with three exceptions: they have no taint, they let in a bit more oxygen and they are very consistent in oxygen transmission.

    Their consistency is a major selling point to winemakers because the wine will have a predictable taste at various points in time. In fact, winemakers can tweak the oxidation rate of their wine by choosing from a range of synthetic corks with different rates of known oxygen transmission.

    Screwcaps are actually two parts: the metal cap and the liner inside the top of the cap that seals to the lip of the bottle. The liner is the critical part that controls the amount of oxygen getting into the wine. Back when screwcaps were only used on jug wine, there were just two types of liners available. But today multiple companies are jumping in to offer their take on what rate of oxygen transmission is best, as well as to replace the tin used in one of the traditional liners. The standard liners admit either a bit more or a bit less oxygen than good natural corks. Screwcaps, being manufactured, are also very consistent.

    Is there an optimum wine closure?
    Synthetic closures are cheaper, predictable and great for everyday ways. Natural cork is the only cork proven for long-term aging.

    Performance of the manufactured closures, made with 21st century technology, is excellent. Generally they approximate our expectations, based on over two centuries of experience aging with natural cork closures.

    For the regular wine you might purchase for dinner this weekend or to keep for a year or two, any of these closures are perfectly good, while the manufactured closures avoid taint. In fact, your choice is more a matter of preference for opening the bottle. Do you want the convenience of twisting off the cap, or do you want the ceremony of removing the cork?

    For long aging however, the only closure with an adequately long track record is natural cork. So to be safe, that is the closure to choose. Once we have solid long-term evaluations of synthetics and screw caps, it will be possible to judge their suitability for extended aging, such as more than ten years.

    Over centuries, winemakers have consistently taken advantage of new technology to improve their product, from oak barrels to bottles to modern crushing and pressing equipment and micro-oxygenation. While manufactured closures have some key advantages, it is proving difficult to displace natural cork due to its centuries-old tradition, albeit with a few problems, and its connection to the natural environment.

    Further reference:
    Nancy MILLS, Paulo LOPES and Miguel CABRAL
    ‘Australian consultant ‘Amorim’s Research and Development Department

    However, the preliminary results of a more recent study by the University of Porto’s Department of Chemical Engineering suggest, for natural cork closures, that most of the oxygen diffuses through the closure, although some permeation through the cork-glass interface was also found (Cristiana Pedrosa, University of Porto, pers. comm.). The Porto researchers used the Wicke-Kallenbach method, a Mocon- like test that uses different concentrations of oxygen on either side of the cork to drive the movement of oxygen, but maintains the same total gas pressure on both sides of the cork. The study was partly funded by Amorim.

    By Paulo Lopes, Isabel Roseira, Miguel Cabral, Cédric Saucier,
    Philippe Darriet, Pierre-Louis Teissedre and Denis Dubourdieu

    Paulo Lopes, Cédric Saucier, Pierre-Louis Teissedre, Yves Glories
    Faculté d’Oenologie de Bordeaux

    David P. Faria, Ana L. Fonseca, Helen Pereira, and Orlando M. N. D. Teodoro,
    Center for Physics and Technological Research CEFITEC, Physics Department, Faculty of Sciences and Technology,
    Universidade Nova de Lisboa, Portugal

    January 2017

    John Casey | 28 April 2018

    6 I agree. Post-bottling oxidation can be caused by a number of different factors, and the one that is exclusive to cork stoppers is the length of the compression stroke. Problems began in Australia with the very rapid increase in the volume, speed and mechanization of bottling operations accompanied by the dilution of skills and the very bad “expert” advice to reduce the levels of SO2. Any entry of atmospheric oxygen is between the closure and the glass and is pretty much the same for current metal caps and cork stoppers

    jonathan snashall | 27 April 2018

    yep is seems the debate is alive and well – yep John corks don’t breath but i have read of gas exchange between the cork and bottle neck. One would imagine that wines that suffer random oxidation as you describe would be prone to it due to low SO2 and / or high dissolved oxygen, after all only so much O2 can be trapped in the neck.

    Marc R Kauffman CS, CSW | 26 April 2018

    Michael I don’t think it’s ever been “a war” but certainly a matter of differing opinions. Most vehement participants are the closure suppliers themselves, be they cork producers, Nomacorc metal screw cap (Stelvin et al), Novatwist or Vinolock. Most winemakers agree there is no one perfect closure for all wines. Consumers really don’t care as long as the wine tastes good. Research has shown consumers do not base wine purchase on a closure choice!

      John Casey | 27 April 2018

      There are a number of misapprehensions in this article.
      1 Although cork is permeable to gases and vapours, when compressed in the neck of a bottle it provides an effective barrier to the entry of atmospheric oxygen. This was demonstrated comprehensively by researchers in Bordeaux in the 1930s. Their work demolished the “breathing corks” hypothesis and provided the rationale for the development of metal caps with oxygen-impermeable wads or gaskets.
      2 So-called “random oxidation” is caused largely by inadvertent compression of headspace air by the incoming cork when the corking machine is run at slow speeds and/or when there is ineffective application of vacuum or CO2 flushing.
      3 The acquisition of TCA is largely an environmental problem also experienced by the food an packaging industries. Although the rate can be extremely variable, several large scale surveys have put the figure at around 1-2% or less.
      4 Exclusion of oxygen contact causes a spontaneous reduction of the oxidation status of the wine as measured electrically by the ‘Redox Potential’. Data produced by LBM showed the same lowering and seasonal fluctuations of Redox Potential for cork and various wad formulations. The reason that cork-sealed wines are not plagued by SLO (sulfide-like odours) is because they are absorbed by the cork.

    Pierre Rabie | 26 April 2018

    Michael that was a very lawyerly (??) written opinion (piece) you may have missed your calling 😉 You will not remeber but you were the very first expert I had to wrestle with in my career as a lawyer – a long time ago – the fruit from that very (in)famous tree…

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