Jamie Goode: Has the industry made any progress when it comes to closure performance?

By , 1 February 2023



Packaging wine is hard. Harder than you’d expect, and harder than anyone realized until they started looking for an alternative to glass bottles sealed with a cork.

Back in the day, of course, most wines never made it to bottle. We are talking a few hundred years ago. They’d be shipped in barrel, and if they did see a bottle it would be a temporary home for most, because bottles were expensive and were re-used. Even as recently as the 1970s, a lot of wines were sold to local customers in bulk: they brought along their own containers, and got them filled at the winery. And lots of ordinary wine was sold in cheap plastic bottles, meant for short-term consumption.

Gradually, though, increasing volumes of wine were being bottled and sealed with cork. By the late 1990s, the cork manufacturing plants, most of which were in Portugal and Spain, were under pressure. More wine than ever was being put in bottle, and corners were being cut.

Cork manufacture involves stripping the bark, then taking the planks, bundling them up, and leaving them to season outside before processing. Some cork was already contaminated with musty taints at the point of harvest: trichcloroanisole (TCA), the main taint compound, is produced by microbes found in the bark. But leaving these bundles of cork on bare earth wasn’t helping. Then the cork is boiled before processing, and the way this used to be done cross-contaminated good cork planks with bad.

Taint has always been as issue with cork, but by the end of the 1990s it seemed to be at a very high level, especially for those far away from Europe who were at the back of the queue for cork. In Australia, in particular, taint rates were well over 5%, and then there was a problem with inconsistency that led to issues with oxidation.

So there was a pressure for alternatives. Screwcaps had been trialled in the 1970s in Australia, but there was no consumer traction. In the mid-1990s plastic ‘corks’ were the next to be trialed: issues with consumer acceptance seemed less problematic because these were in-neck closures that still required a corkscrew. The first ones were injection-moulded plugs, although extruded plastic came along a few years later. These did a fine job keeping the wine in, but with their more widespread use winemakers soon began to realise that there is more to sealing a wine than keeping the liquid in the bottle. After a short while the wine began to oxidise: oxygen was diffusing through the body of the cork, a major issue with plastic.

Then in the late 1990s Australia once again trialed the screwcap, and this time it was a hit. But, again, it turned out that the job of the closure is more than just providing an effective seal. The screwcap isn’t the actual closure: it is a way of holding the wadding in tight apposition to the rim of the bottle, and it’s the oxygen barrier properties of the wadding that are important here. The liner chosen for wine is called tin/saran, and the layer of metal in the liner prevents any oxygen transfer. And when it came to the first large-scale closure trial, started by the Australian Wine Research Institute in 1999, they made some interesting findings. First, the plastic corks in the trial resulted in wines oxidising fairly fast. The natural corks were variable, but the good ones much better. Technical corks, made up of bits of cork glued together, were consistent, but had issues with taint: chopping cork up and glueing it together averages out any TCA present, and sometimes there’s enough to result in a musty taint. The screwcaps performed really well, but those sealed with the tin/saran liner, while they preserved the fruity qualities of the trial wine best (a Clare Valley Semillon), resulted in slight issues with a struck flint/rubbery reductive character in the background. It seems that a super-tight seal (in terms of oxygen transmission) isn’t really ideal, although it’s a lot better than plastic.

After a big initiative in the Clare Valley with the 2000 vintage, when Clare winemakers, frustrated by the poor performance of cork, banded together to make a stand on the issue. Clare is famous for its Rieslings, and these wines are made in a style that shows up any cork-related faults particularly transparently. The Clare winemakers had to overcome a significant logistical obstacle before they could offer their wines in screwcap: at the time, there was no Australian supplier who could offer bottles and caps of the required style and quality. As a result, they had to drum together enough like-minded producers willing to adopt screwcaps to generate an order for 250 000 bottles from Péchiney in France, which was the threshold needed to make this possible. With a collaborative effort, they managed it, and the combined shift was large enough to make headlines, for what at the time seemed a very brave move. Jeffrey Grosset, one of the winemakers involved, estimated that from this humble beginning, during the 2004 vintage 200 million wine bottles were sealed with screwcaps in Australia, taking roughly 10% of the entire Australian production in just four years. Now it is hard to find a wine in an Australian bottle shop that has an in-neck closure. New Zealand has also made a dramatic shift, and is almost exclusively a screwcap country now.

But while the writing seemed to be on the wall for the cork, the current situation sees cork maintaining the majority of the market share. Estimates are that 20 billion wine bottles are sealed every year, and of that 6-7 billion are screwcapped, between 1-2 billion are sealed with synthetic corks, and the rest are sealed with natural cork. How has cork got annual sales of around 12 billion units when it was causing so many problems just 20 years ago?

The answer lies in the fact that wine is still quite a tradition-bound product, but also in the steps the cork industry has finally taken to sort its issues out. The first of these was upgrading production facilities, including storing cork bales on concrete, and then cleaning the boiling water between batches. The second is the adoption of curative technologies designed to get any taint out of the cork. This step is also tied in with a move to technological corks and the elimination of cheap natural corks from the market place. It’s much easier to clean cork granules than it is intact natural corks (which tend to get distorted). The cleaning technologies include steam and critical point carbon dioxide (developed by Diam, but now out of patent so Amorim also have a version running). And third, there are methods for catching any tainted corks before they get to the customer. Amorim’s NDtech is an example of this. As a result, cork taint rates have gone down. Last year at the International Wine Challenge over 13 000 bottles were opened, and of the cork-sealed ones, around 0.8% were deemed tainted: it’s still too many, but a vast improvement.

Screwcap sales are growing, and a range of liners with different oxygen transmission levels are being offered. For sparkling wines, Oeneo’s Mytik Diam is a taint-free technical cork option that is selling very well. Cork companies speak bullishly about their prospects despite a short cork harvest in 2022 and increased prices of raw materials, energy and transport issues (although these latter three issues have impacted all closure manufacturers).

So has the closure industry made any progress when it comes to closure performance? The answer is yes, a lot, and rapidly. The problem is that sealing a wine bottle is a complicated thing: wines are susceptible to oxidation in a way that spirits are not, and also the nature of post-bottling wine chemistry is that reactions can occur that produce undesirable sensory outcomes if the level of oxygen transmission by the closure is too low. It’s when it comes to closures for fine wines that we run into particular issues – we want a consistent level of oxygen transmission, but not very much at all, and it may well be that release of phenolic compounds from natural corks has been contributing to the way that fine wines age over many years, and this would be difficult to replicate using a non-cork closure. It’s frustrating to admit that there is no perfect closure, and that sometimes winemakers just have to choose the compromises they make in choosing one of a number of good but not perfect solutions when it’s time to bottle.

  • Jamie Goode is a London-based wine writer, lecturer, wine judge and book author. With a PhD in plant biology, he worked as a science editor, before starting wineanorak.com, one of the world’s most popular wine websites.


3 comment(s)

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    Neil Tabraham | 2 February 2023

    A well written and considered article which avoids the emotive issues relating to cork and screwcaps. However, there is one point that often gets forgotten about and that’s sustainability. In my professional capacity, I open hundreds of bottles a year, many of which are under composite or real cork. I’m personally quite sensitive to cork taint whether it’s TCA or otherwise, but I’d have to question whether there are anywhere near the 0.8% failure rate you suggest. Personally, I’d put it at close to 0.1% if I were to be realistic.
    The biggest issue though is cork is a sustainable and degradable product. Screwcaps are not, regardless of progress to immitate cork more closely. As such, we need to ask what consumers prefer in this instance. There’s clearly a convenience to screwcaps and they reseal a bottle more effectively. That may suit some consumers, but what about producers? And what about the environment? If we’re to engage with younger wine drinkers, why aren’t the marketeers pushing corks to a generation that are hugely concerned about protecting the environment? Considering who the future of wine is, are we not missing a trick simply because our views are tainted by the past?

    jamie goode | 2 February 2023

    Igor – re that suberic acid story – if it was a good study why was it published in a middling trade magazine rather than a peer-reviewed scientific journal?
    Also, if Diam had glue issues, would they be selling 2.5 billion closures annually?

    Igor Ryjenkov MW | 1 February 2023

    On the subject of the technical closures – as a consumer, I personally am not as confident as one would like to be that they are as taint-free as they claim to be, depending on how one defines taint. Even if they are TCA/TBA-free (e.g. below detectable), unintended compounds such as suberic acid may be getting into the wine, impacting wine’s astringency in the case of this acid, please see the link below. That research somehow did not get much press coverage, but given the level of the new-gen technical cork acceptance, it really should. There have been also instances of gluey-ness reported with these products, one I experienced first-hand, as well as sizeable swings of bottle variation that these closures are meant to also eliminate.


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