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Testing for Cork Taint
© Sue Courtney
15 July 2001

Kumeu River winemaker Michael Brajkovich, Master of Wine, quotes Stephen Henschke as saying "All wines closed with natural cork are tainted - it's just a matter of degree".

And what degree is too much? "Any more than 1-3%". Unfortunately a figure as low as this is almost impossible to reach so until now the acceptable limit has had to be higher.

Every batch of corks that comes into the Kumeu River winery is rigorously tested.

Fifty corks from each batch of 10,000 are fully immersed and sealed into individual plastic vials containing a solution of neutral (untainted) white wine for 24 hours at a temperature of 25C.

Corks are removed and the soaking liquid is poured into wine glasses to be given the MW nose test. Some batches have had over 30% taint. Any batch that returns over 4-6% taint is rejected. "If we didn't accept batches with as low as 4-6% taint, we would have a problem" says Brajkovich.

One time they were very excited. A batch from France was free of cork taint but this elation lasted only until the next batch arrived from the same source - it was one of the worst ever tested.

But it is not only cork taint that is being tested. The results of these experiments show that corks impart colour to the wine too. These results have been followed up with water testing, which has seen the water change to a watery white to a 10-year old chardonnay colour.

The tainted corks are retested over and over - the taint does not go away.

Jeffrey Grosset in the Clare Valley found that microwave techniques do not solve the problem, either.

What these winemakers find hard to accept is that the batches of cork they reject will be sold to someone else.

"Price of cork has never been an issue" says Brajkovich. "We went for quality but the quality wasn't always there".

There has been unacceptable corkage taint in Kumeu River Chardonnay from the 1998 and 1999 vintages, but for the 2000 vintage, one of the best on record, rigorous testing has found batches with a maximum 1-3% taint. These will the batches of corks used on the 2000 production.

As for 2001, well - the winner is the screwcap. Kumeu River will bottle all of their Kumeu River Pinot Gris 2001 in Stelvin screwcap closures on the first bottling run this coming August. I'll be there with my camera.

Other 2001 vintage wines, including the reds, will follow suit with some in Stelvin screwcap and some in corks that come from low cork tainted batches.

© Sue Courtney 2001

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