The lottery that is cork

It was reported recently that 90 per cent of Australian wine is now sold in screw-capped bottles. One reason for this massive swing is cork-related taints such as TCA; the second and less-known reason is random oxidation. Because of variability in natural cork’s porosity, wines under cork age at an irregular, and unpredictable, rate.

I’ve opened a dozen bottles of the same five-year-old white wine (all aged in the same box in the same cool cellar) and found almost every bottle different: some oxidised and gone, some corked, some perfect and the others all at varying rates of advanced maturity. If they’d all been screwcapped, they would likely be all as good as the bottles with perfect corks. That is, pristine and fresh. I recently saw this scenario repeated, albeit on a small scale.

I opened a six-pack of McWilliams Mount Pleasant Elizabeth Semillon 1997, which had been in its unopened box in my cellar since it was released. The accompanying picture shows the variation in colour, which reflects the varied speed of aging, due to cork variation. I chose the fourth bottle from the left to serve to special overseas guests. I could see from the colour that it was likely to be the best. It was superb. But I could also tell from the colours that one of the bottles is completely oxidised, and two or three others are probably going to be tired and prematurely old.

This is the problem with cork. Delicate white wines such as Hunter Valley semillon are most vulnerable. Full-bodied reds, less so – and the advanced development is not nearly as detrimental to the taste.

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