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.