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News special: IWC's wine fault analysis

Published:  23 July, 2008

By Paul White - Anyone who has watched the wine closure debate closely over the past few years will have noticed the almost complete absence of objective statistics available to tell us how corks, synthetics and screwcaps actually behave in real-world conditions.

For this reason alone, the International Wine Challenge's (IWC) recent first attempt at collating data on wine faults is a good start for a worthy cause.

That said, the IWC's analysis stumbles in attempting to separate out faults as either closure caused or native to the wine. Fault identification is one thing, but ascribing faults accurately to a wine or its closure is much more problematic. Short of expensive testing, followed by carefully tracking a wine back through all its processing stages, attribution can't really be done with any degree of accuracy.

There are many documented instances where TCA - which is the easiest wine fault to pick out - was initially blamed on the closure and found later to be endemic to the winemaking or the winery. This problem gets even harder when dealing with faults like oxidation and sulphide reduction.

Let me explain using an example. I recently tasted a Pinot Gris bottled under screwcap which was both oxidised and seriously stinky from sulphide reduction. A second bottle showed the same problems. I have no idea whether the wine was oxidised during winemaking, at bottling or after. The same would be just as true for an oxidised wine found under cork or synthetic.

I also have no idea whether the same Pinot Gris wine was bottled dirty' with serious sulphide problems or was bottled clean' and then developed sulphide problems under anaerobic conditions post-bottling. There are five variables at play here and both faults could sit side by side under various permutations of each. Sam Harrop's belief that sulphide reduction derived from inappropriate winemaking techniques when using screwcap closures' can somehow be separated out from excessive sulphides not directly linked to closure' ignores the chemistry of sulphide behaviour. It is humanly impossible to know the origin of these faults purely from sensual evaluation.

And this reflects back to the core problem with the IWC's results. Unless the IWC has done some eloborate behind-the-scenes analyses of these wines to further corroborate their stats - which isn't clear to the reader - then its analysis is deficient. The reasons for separating faults out as closure or wine related don't make sense, while the current references, couched in percentages of percentages, obscures a clearer association between oxidation, reduction and closures.

It seems to me it would have been more useful to have sectioned out TCA, sulphide reduction and oxidation as percentages of natural cork, technical cork, pro-cork, synthetic, plastics, zorks and screwcap. Any likely association would have been instantly clear, and any further qualification could have been added to clarify issues. It would also have generated useful figures for oxidation under screwcap or synthetics, wine-related TCA generally, and reduction under synthetics and cork.

Picking up on Harrop's surprise that sulphide reduction is a bigger issue than previously suspected, I'm not at all suprised. My belief is that it is a much bigger issue than most people realise. Recently, while judging with a panel of five at Mondial du Bruxelles, I ran across several wines with serious sulphide issues. After bringing these to the attention of the panel leader, a winemaking academic from the University of Bordeaux, he agreed they had sulphide problems and that he had already tossed them out of contention. Assuming all bottles would be equally bad he saw no reason to draw up a second bottle for a retaste, so those wines never showed up in the fault statistics.

Going hand in hand with this is another common problem. Few judges are able to accurately identify sulphide reduction. They may feel its negative impact on fruit and a palate bitterness, but fail to peg the fault for what it is, marking instead as a poorly made wine. I've noticed this happening at many wine competitions; sulphidic wines, unlike TCA tainted or oxidised, are rarely identified, and when they are, rarely given a second look. Expect to see a lot more of it.

Apart from this quibble, the IWC deserves to be commended for a good start. With a little tweaking, it should be able to deliver some fairly precise and accurate information in the future.