Looking for Closure: Screwcaps vs. Corks

[Craig Camp]

In the latest newsletter from Amorim, they offer a synopsis of a recently completed Bordeaux study on oxygen transmission rates:

The picture that has emerged puts natural cork into an intermediate position in terms of oxygen transmission rates. The natural corks allowed between 0.1 and 2.7 microlitres a day during the period from 12 months to 36 months. In comparison, over the same period, the synthetic stoppers let in much more oxygen while screwcaps let in noticeably less.

Research by the Australian Wine Research Institute has suggested that reduced or 'rubbery' aromas can develop in wine sealed under screwcap as a result of the closure's low OTR. The same researchers found that wines under synthetic stoppers tend to lose fruit attributes and develop oxidised or 'wet wool' aromas.

Cork, it seems, appears to allow some, but not too much, oxygen into the wine, preserving fruit intensity and minimising the tendency for reduced characters.

Wine experts and consumers already have a layman's appreciation of how a wine develops under cork over a period of years. But the scientific basis for this process is not well described. For example, it is not clear how oxygen actually enters a cork-sealed bottle.

Amorim is funding research to gain a better understanding of oxygen entry — for example, to determine whether oxygen diffuses through the cork from the atmosphere or comes from within the cork itself.

'Impact of storage position on oxygen ingress through different closures into wine bottles,' Journal of Agricultural and Food Chemistry, 54(18), 6741-6746, 2006.

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IMO reduction issues under screwcap are a function of winemaking errors not closure issues. If enough oxygen is in solution the wine will not go into a reductive state. There are certainly plenty of examples around of severely reduced wines in cork finished bottles. I don't believe the amount of oxygen they are referring to in this and other studies can make the difference when it comes to reductive issues.

[kitchensqueen]

Just to throw in my two cents...

At first, I was pretty annoyed with the move towards synthetic corks and screw caps, because I like the ritual of properly opening a bottle of wine and that's the way it's always been done. For some reason, I (and I think a lot of others) are just attached to that.

However, I'm starting to change a little bit. I'm notorious for corking the wine. Nearly without exception, no matter how careful I am, I will pierce the cork. And sometimes that cork (on that expensive bottle) will shatter into dust and no amount of filtering and decanting will get rid of it. That's disappointing. The synthetic cork makes me feel competent, and we end up with drinkable wine.

And there are some times when a corked wine actually isn't convenient - picnics, camping, etc. it's nice to take a minimum of stuff and have minimum effort.