Screwcaps, plastic or cork? What are the issues

Have you noticed the increasing number of wine bottles sealed with screwcaps, and wondered why? It’s because of a small war that is taking place. Over the last few years, the wine trade has been embroiled in a conflict. You wouldn’t have thought that the rather boring-sounding issue of bottle closures would inflame passions, but it has, and to a remarkable degree. One the one hand we have the traditionalists who feel that cork is the only decent way to seal a wine bottle; on the other we have the screwcap crusaders who are on a mission to eradicate cork and have all bottles sealed with alternative closures. Who’s right?

Cork is a remarkable natural substance. Because of its cellular wall composition and structure and it has elastic and compressible qualities that make it ideally suited to sealing wine bottles. A decent cork will provide a good seal on a wine bottle for thirty years, possibly longer, allowing the wine to develop and mature into something special. And despite corks providing a good seal, it’s relatively easy to extract them using one of a wide array of different designs of corkscrew. Added to this, taking the cork out has become a valued part of the tradition of wine. It may sound silly, but there’s something special about uncorking a bottle.

So what’s the problem? The dirty secret of the wine trade is that one in twenty bottles of wine is ruined as soon as it is bottled by problems with the cork. Chief among these is what is known as ‘cork taint’. This is when a wine takes on a musty odour caused by a chemical called 2,4,6-trichloroanisole (TCA) that is present in some corks. TCA itself is produced by microbes that live in the small pores, called lenticels, that run throughout cork bark. In extreme cases it’s hard to miss a ‘corked’ wine: the mustiness can sometimes be overpowering. In other situations the taint is more subtle, reducing the fruitiness of the wine, giving it a subdued aroma, usually with a faint whiff of damp cardboard or old cellars in the background.

The problem with TCA is that it is incredibly potent: most people can detect it at concentrations as low as 5 parts per trillion, which makes it hard to eradicate. To give you a better idea of this figure, it’s equivalent to one second in 64 centuries. Where good data have been collected, the frequency of cork taint hovers around 5% of bottles sealed this way. The other main problem with corks is that because they are a natural product, they are variable, and some fail by letting oxygen in which then spoils the wine.

Cork taint hasn’t always been such a big issue. In the past it is likely that many people weren’t as aware of the problem and happily drunk corked wine. But with the increasing quality of cheap wine (which makes any taint more likely to be spotted) and the fact that consumers are now generally better informed, a vocal body has sprung up who have decided that they’re not going to put up with this situation any longer.

The cork industry has been slow to address the issue. Initially they went through a period of denial, funding PR campaigns to persuade people that cork is the natural option. They hid behind an environmental smokescreen, claiming that if people ditched cork, then the Iberian cork forests—a precious ecological resource—would be under threat. Finally, they realised that research on the problem would be a better use of resources, and while there are now some promising techniques in development, there is still no solution that results in taint-free corks. 

So what are the alternatives? Surprisingly, modern science hasn’t been able to come up with a synthetic substance that shares cork’s properties of elasticity and compressibility. While there are a number of synthetic corks on the market, they’re really only suitable for wines destined for immediate consumption (that is, within a year or two). The problem has been that the plastics used can’t provide a seal equal to that of real cork without being impossible to extract from the neck of the bottle. The result is that plastic corks tend to be permeable enough that the wine tends to oxidise after a couple of years, although they are fine for everyday wines that are usually drunk on release. Of course, it should be pointed out that some makes of plastic cork are more efficient than others, and product development is occurring all the time, so we may yet see serious plastic alternatives to corks (they may already exist, although I haven’t yet seen good data indicating this). For now, then, the leading contender to cork is therefore the screwcap.

Screwcaps provide a pretty good seal—better than cork, in fact. And they are easy to open: you don’t need a corkscrew, you just twist them off. Because they are manufactured and not a natural substance, they provide a much more uniform seal than corks. Added to this, there are plenty of reports of 20 year old screwcapped bottles being opened and the wine tasting fresh and lively.

So how come all wines aren’t sealed with screwcaps? This is what a vocal element in the wine trade are calling for, after all. There are three main problems. First, screwcaps have a ‘cheap’ image in the minds of many consumers. People associate screwcaps with bargain basement plonk. Some markets, particularly those in traditional European wine producing countries, are highly resistant to alternative closures such as screwcaps, whereas others, such as Australia and New Zealand, are more accepting. Second, people like corks. They’re natural, they look and feel right, and the ritual of getting the corkscrew out is part and parcel of the wine drinking experience. Thirdly, while most experts agree that the screwcap is the closure of choice for fresh white wines and easy drinking reds, there’s some debate about whether they are suitable for red wines destined for long ageing.

The reason for this doubt is that people like the way that fine wines evolve over time when they are closed with a fault-free cork. Screwcaps provide a better seal than cork. The question is, is this seal likely to be so good that it prevents the wine from ageing properly over, say, 20 years? Wine ageing is a complex process that takes place largely in the absence of oxygen, in what is called a ‘reductive’ environment. But could it be that the trace amounts of oxygen that get through the seal provided by the cork are an intrinsic part of the ageing process? The scientists don’t know for sure, and as yet no one has done the proper experiments that will settle this issue once and for all.

However, it is worth emphasizing that only a very tiny fraction of the wines made worldwide will require extended cellaring. For almost all other wine styles, the screwcap is likely to be the optimum closure. It’s likely for one reason and another that cork will always be with us, but unless someone comes up with a cure for the curse of cork taint, expect to see screwcaps gaining ground over the next few years.

© Jamie Goode, 2004

This article is a modified version of a piece written for Hong Kong Tatler, January 2004
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