It's a truth almost universally acknowledged that corks aren't the ideal way to seal a bottle of wine. As a natural product they exhibit a fair bit of variability, and¾ worse still¾ a relatively high proportion of them (1-7%, depending on who you listen to; most likely around 2%) taint the wine at source with the musty smelling compound trichloroanisole.

This is the source of a great deal of frustration for wine lovers. Few experiences are as dispiriting as opening a carefully cellared prize bottle only to find that it smells of damp cellars and games kit that's been left in a school locker all term. The unacceptable cork failure rate has led to the deployment of synthetic corks and the increased use of screwcaps (commonly known in Australia by the trade name 'Stelvin'), which offer a taint free seal. These are now commonly used for inexpensive wines, although not in markets such as France where there is still widespread consumer resistance.

In light of this, it's easy to forget just how good a seal corks are when they aren't tainted and they don't fail. Cork is relatively inert, it is compressible, it is elastic, and it will provide a good seal for at least a decade (often far longer). With a paucity of decent data it's a matter of speculation as to how much of the significant bottle variation that occurs in older wines is caused by variable cork performance. Most likely, the loss of elasticity in older corks renders the wines they protect more vulnerable to poor storage conditions. A wine sealed with an inelastic, shrunken cork is much more likely to let a bit of air transfer occur when there's a fluctuation in temperature than one sealed with a young, elastic cork. This is why knowing the 'provenance' (how the wine has been cellared) is absolutely critical if you are thinking about buying older wines.

What's happening? I hear regular readers ask. Is this the same writer who has until recently crusaded for the cause of the synthetic cork? (Yes.) Have I suddenly entered the pay of the cork manufacturers? (Not at all. Never.) What I'm suggesting is that when corks work well, we like the way they work. I'm very happy to see everyday drinking wines that aren't intended for long-term cellaring sealed with synthetic corks and screwtops. This is a good thing. Am I happy to see my fine wines sealed with such alternative closures. No, not yet. Here's why.

Quite simply, I'd rather risk cork taint in a few bottles than risk ruining my entire cellar. People who cellar wine do it in the hope that the wine will evolve with age in a certain way, presumably because they like the way that similar wines have aged in the past. And no one has yet demonstrated how intrinsic the cork is to this ageing process. The question is, how do we want synthetic corks and screwtops to perform over the long-term? Do we want as close to a hermetic seal as possible? I'd argue that what we want is for alternative closures to mimic as closely as possible the performance of a good natural cork—no better and certainly no worse. While it's clear that corks don't allow very much air transfer (if they did the wine would rapidly disintegrate), they may allow just a tiny amount. And this may be a factor in the normal the ageing process. We just don't know.

Repeated claims have been made that Australian Rieslings and New Zealand Sauvignon Blancs sealed with screwcaps taste fresher than those sealed with conventional corks. This should be a cause for alarm when it comes to thinking about using these closures for fine wine. For fresh white wines and even some lighter reds, this may be seen as an improvement. But most fine wine buffs don't want their favoured tipples 'improved' in this way. They're quite happy with them the way they are, and would see it as a disaster if the character of Grand Cru Burgundy or classed growth Claret was to be altered by using a different closure.

What are currently lacking are independent, statistically robust data showing how alternative closures perform over extended periods. The best current data are those from the Australian Wine Research Institute, who published the results from the first two years earlier this year. Interestingly, there already seems to be a difference in the data between conventional corks and screwcaps; I'll be following this study with interest over the next few years. Proponents of screwcaps argue that some Australian Rieslings have been sealed with these for a couple of decades, and the wines age very well, retaining a high degree of freshness. The problem with these sorts of anecdotal data is that there are just too few data points and no controls. The worry is that what's good for Aussie Riesling might not be so good for classed growth claret. Until the data show that the performance of the various alternative closures closely tracks that of natural cork over extended periods, I'll probably stick with the latter for sealing wines I'm intending to cellar for more than a couple of years.