Corks, Synthetics, and Screwcaps

Posted by Alan Boehmer Apr 10, 2007

Cork is an amazing substance! It seems to provide an ideal closure for wine bottles. That is, if it is free of TCA (a naturally occurring chemical sometimes found in cork). It's been shown that around 5% of all wine sealed with cork shows perceptible amounts of TCA, usually at levels that result in spoilage. It's been said that one drop of TCA in an Olympic size swimming pool would be perceived by most people.

A great advantage of cork, according to many winemakers (although the jury is still out on this), is that it allows wine to breathe ever so gently. It is now understood that oxygen in excessive amounts will spoil a wine, but in micro amounts can actually prevent certain undesirable qualities from developing. These "cooked vegetable" or "cabbage" aromas and flavors are said to be products of reduction - a chemical process that takes place in the absence of oxygen.

Synthetic corks to the rescue! Well, not so fast. Synthetics, while loudly applauded upon their introduction around 15 years ago, have not stood the test of time. It appears that if you are able to get them out of the bottle at all, they will not protect your wine over more than a few years' time.

Screw caps of various styles are the latest trend. But again, don't be too quick to form your opinion of them. First, the efficacy of a screwcap depends entirely upon the material used for the lining-the part of the closure that comes in contact with the wine. And guess what? The best linings in recent trials have been shown to be made of cork!

The best screwcap closures used in North America and Europe at this time are the Stelvin closures. While not really a screwcap at all (they are machine molded to the neck of the bottle), they are the closure you will find on almost all quality North American wines that do not use corks or synthetics.

How will wines age under Stelvin or other screwcaps? Will wines so cellared be subject to reductive processes over time? We don't know. That's why virtually all producers of great wine intended for long cellaring still use cork. The flip side of the matter is that wines not intended for storage more than a few years will benefit from the superior seal that screwcaps provide.