There’s a wonderful throwaway line in Harry Potter and The Philosopher’s Stone. “God I miss the screaming,” says scary caretaker Argus Filch, lamenting the fact that detentions at Hogwarts no longer involved hanging kids up by their thumbs in the dungeons. 

It’s a bit like that with the wine bottle closures debate. In the past you could guarantee a bit of a verbal punch-up, it was such a contentious issue. Screwcaps versus corks. Fight! Fight! Now it has all rather calmed down, and how I miss the fighting. [Declaration of self-interest: the controversy surrounding closures led to lots of commissions to write on the topic.] 

Since their reintroduction in Australia with the 2000 vintage, screwcaps have seized a large slice of the market from natural cork and their sales are steadily growing, although a recent Wine Intelligence report showed that they are still not very well accepted in the US market. 

Synthetic corks have got their own significant slice of the market and, despite a dramatic consolidation among producers, have hung on and even grown sales, with a particularly strong showing in the US and France, countries which haven’t readily embraced screwcaps. 

And natural cork – including the very successful category of technical corks – still has very robust sales figures. In part, this is because the market has grown, so there has been plenty of room for new entrants. But there’s also a conservatism in many markets that maintains the place of cork. 

Exact figures are hard to come by, but from speaking to the various players – each of which have their own estimates – my guess at the current breakdown in closure use would be as follows. 

The overall marketplace is 18bn-20bn worldwide each year, a figure that most closure companies seem to agree on. Screwcap sales are still growing and are around 5bn, while synthetic corks are around 3bn. The rest of the market, some 11bn or so, consists of natural cork and technical cork, with alternatives such as Vinolok (the glass stopper with an aluminium cap) and Zork having only a very small slice of the market. 

Here, I’m ignoring small serve (below 37.5cl) bottles, which are almost exclusively screwcapped, and we also need to consider the impact of alternative packaging such as bag-in-box and pouch. The growth of these could impact on the volume of wine bottled, and therefore on total sales of closures.

Evolving market

The closures market has evolved significantly since screwcaps first appeared on the scene and shook things up a lot in the early noughties. Back then, there was no appreciation of the important role of oxygen transmission in post-bottling wine chemistry. This has now been explored scientifically, thanks in large part to research sponsored by synthetic closure company Nomacorc, and the major closure types, with the exception of natural cork (which can’t), have embraced the idea of offering closures with different oxygen transmission levels that winemakers can then match with wine style.

The Champenois were the first to embrace this idea. Up until the end of the 1960s champagne did its second fermentation on natural cork. Then, in the late 1960s the crowncap was introduced, which at the time had a cork liner. 

“Producers found it was much easier to work with crowncaps,” says Benoît Gouez, chef du cave of Moët & Chandon. “This was perfect for non-vintage or young vintage releases, but they found they weren’t ageing as well as wine bottled with natural cork.” 

These days Moët uses crowncaps with different liners, depending on the wine. For wines destined to be aged on lees for a long time, it uses crowncaps with lower oxygen transmission liners. 

But for their own private collection they still use natural cork, in part because the crowncap liners can’t match the low oxygen transmission rate (OTR) of good corks, and also because Gouez believes that cork brings something to the wine: “A layer of flavours.” 

Now this idea of using OTR as a winemaking tool post-bottling is catching on with other closure types. Diam was the first to adopt it, offering its engineered technical corks at a range of OTR levels. The cork is made from a mix of cork flour, synthetic microspheres and food-grade binding agent, and varying the ingredients changes the OTR. Diam is available in very low, low or medium OTR forms. 

Significant research

Nomacorc has invested significant sums in sponsoring research into the effect of varying levels of OTR on wine development across a wide range of wines. 

The idea behind this work is both proof of concept and also to provide a data framework from which it can offer winemakers specific advice about which product from its portfolio would best suit their wines. Now it offers a range of OTR levels in its Select series of synthetic cork. 

Significantly, the company has made two further steps that look likely to breathe life into the synthetic category. 

The first is a dramatic improvement in the visual appearance of the closure, with end printing and a grain effect. The new generation of Nomacorc looks very impressive indeed, and is a million miles away from the horrible aesthetics of first generation plastic corks. 

The second is the development of Select Bio, a range made with a proportion of plant-derived rather than petroleum-derived plastic. “We have been certified by Vincotte in the 60%-80% plant-based polymers category,” says Nomacorc’s brand communications manager for the Americas, Katie Myers. 

The next generation Select Bio has just been launched and is a stunningly good-looking closure. And now screwcaps have joined the engineered OTR party with the two biggest players both announcing a new range of liners with a spread of OTR levels. 

Screwcaps consist of two components: the cap itself, and the liner or wadding. The liner is important: it is this that determines the oxygen transmission properties of the closure. 

Silver lining

For a long time, screwcaps came with only two liners for wine use – Saranex and Saran Tin. You can tell the two apart quite easily. The former has a white appearance, while the other is shiny silver. The first (the white one) is composed of a polyethylene (PE) wadding with an inert Saranex layer (referred to as Saranex). This is a multilayer film developed by the Dow chemical company that acts as a gas/water barrier. 

Technically speaking, Saranex is a PE/ethylene vinyl acetate (EVA)/Saran/EVA/PE heat-sealable coextruded barrier film. The second liner (silver appearance) differs because it has a thin tin layer (sandwiched between the polyethylene and a thin polyvinylidene chloride [PVDC] outer skin) that acts as an oxygen barrier. 

This oxygen barrier doesn’t have to be tin – it could be another metal, such as aluminium. Virtually all of the screwcaps used in Australia and New Zealand have this metal layer, and thus have extremely low oxygen transmission. The most common version of this type of liner is Saran Tin. Saran is the trade name for polymers of PVDC, developed by Dow, which has low water and oxygen permeability. 

For a long time it was used to make Saran wrap (now this wrap, also known as cling film, is made solely from polyethylene because of safety concerns, although it is now less effective as an oxygen barrier). In Europe, particularly in Switzerland where screwcaps have been used widely for a long time, it’s mainly the Saranex liner that is used, which has a higher rate of oxygen transmission. 

New ranges

Amcor recently introduced a new range of liners called Stelvin Inside. This is a new range of four different liners, with all the films being produced by Amcor with a view to offering winemakers alternatives to the two existing liners Saranex and Saran Tin. 

The Stelvin Inside 1O2 liner offers the same OTR target as the existing Saran Tin liner. The Stelvin Inside 5O2 liner offers the same OTR target as Saranex. “Over the years, our customers have asked us if we could provide liners which give new and different permeability levels to those currently available,” says Amcor communication manager Karen Quirchove. “The 3O2 and 7O2 liners are completely new, offering new OTR levels not currently available for wine screwcaps.” 

Even more recently, the largest screwcap producer, Guala, has launched its own range of three liners. Working with Lyon-based Manufacture Génerale de Joints (MGJ), it has developed the Oenoseal liners. 

Onyx has an aluminium layer so has very low OTR, like existing Saran Tin liners. Ivory allows a little more OTR, and Coral still a little more, presumably similar to the Saranex liner. 

So, if you are a winemaker, closures are now a creative tool, and it then becomes a question of matching the right closure to the right wine with a bit of educated guesswork. I’ll conclude by suggesting that, although all is peaceful in this current closure war truce, for the future the biggest threat to sales of all in-neck closures is the continuing steady advance of screwcaps. 

This is because once a winery has made a switch to screwcap, it is unlikely to go back. This is because of the cost of changing bottling lines, but also because what is probably keeping a lot of producers away from screwcaps is fear surrounding market acceptance. 

Once they have made the jump, and seen that the marketplace is happy with the switch, the cost advantages of caps and their convenience to the end user is likely to keep them hooked. And even more so now screwcap liners are now more diverse.