Corkiness in wine. It’s just a smelly little molecule called TCA

I wonder if those same Canberra CSIRO sleuths who identified methoxypyrozine as the magic ingredient in sauvignon blanc might solve the problem of ‘corkiness’ in wine. There’s a fortune to be made if tainted corks can be sniffed out before they reach the bottle.

The unpleasant, musty-cork smell and flavour permeating so many wines comes chiefly from a compound — 2, 4, 6 trichloroanisole (TCA) — formed, I’m told, when cork is bleached with chlorine. When this nasty little molecule remains in the cork, even in the tiniest quantities, it can be leached into a wine sealed with the cork within a day or two of insertion.

Our noses are sensitive enough to detect TCA in concentrations of around four parts per billion. So sensitive are we to it, tests designed to help Australian winemakers detect problem corks rely on the winemaker’s nose rather than on any laboratory equipment for detection.

Corkiness’ varies in degree. In big concentrations it infects wine with unmistakable and strong mouldy and musty aromas and flavours. If you drink wine regularly, chances are you’ve encountered this problem. I wonder how many perfectly good brands we’ve sent to coventry in our minds because of a cork problem.

Corkiness knows no boundaries. I’ve found it in everything from $2.99 Rieslings to priceless old Granges.

Ian McKenzie, joint Chief Wine Maker for the Southcorp Wine Group and Chairman at last week’s National Wine Show here in Canberra, tells me he systematically surveys Australia’s wine shows for corkiness.

It runs at 4-5% and the worst infestations were recorded in Canberra last year two thirds of wines with conglomerate corks were contaminated. As a result producers appear to be using these corks less.

In smaller concentrations TCA may just dull a wine: the aroma and flavour may seem less lively in a familiar tipple, or a new wine not live up to expectations. As well, we all have different sensitivity to it. This seems partly inducible.

At Penfolds Nuriootpa winery, according to winemaker Mike Farmilo, winemakers are sensitised to TCA by exposure to dilute solutions in pure water. He says an accute sensitivity is necessary because a slight taint hidden beneath the raw power of a young red doesn’t go away and becomes more apparent with time. Hence the need to spot trouble early. And sensitivity is also needed for winemakers to participate in screening potential new cork supplies.

Yet concentrations of TCA repugnant to initiated palates may pass unnoticed with others.

Winemakers and show judges become so attuned they can pick TCA with certainty where, in normal drinking circumstances, the rest of us might notice nothing amiss. This sensitivity rises to the fore in the uncluttered and analytical atmosphere of our wine shows.

In the April, 1986 edition of The Australian Grapegrower & Winemaker, J.M. Amon and R. F. Simpson estimate that cork-taint affects 1-2 per cent of all bottled wine in the world. From my own experience on the tasting bench (based mainly on Australian wines) I would say that is a conservative estimate and McKenzie’s rate of 4-5 % appears to be more likely.

For the industry it is a major problem and considerable resources now study it. Alternative closures might finally be the answer. But a good deal of wine’s appeal comes from the romance and imagery surrounding it — and much of that centres on the cork and its removal.

Wine makers generally seem to believe that despite its shortcomings, cork is still the best. So any move to alternative closure looks a long way off.

As consumers we should be aware that any reputable retailer or restaurateur will take back bottles tainted by TCA. In fact, corkiness gives one of the few legitimate grounds we have for rejecting a bottle in a restaurant. Perhaps it’s the only objectionable fault we’re likely to encounter in a modern Australian wine — because its eradication is largely beyond the control of any one wine maker.