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Real Cork, Plastic & Screw-Caps

Many wines are now sealed with closures other than cork. Various forms of plastic cork have been around for some time, and the screw-cap is also increasingly popular.

In response to your questions we have put together a few facts.

Why Use Plastic Corks?
Plastic corks eliminate the problem of “corked” wine and exclude oxygen from the bottles efficiently (at least in the short-term). Unlike real cork they do not dry out and shrink allowing wine to leak out and oxygen to leak in.

What is “Corked” Wine?
This is a fault caused by a defective cork which has reacted with the wine. Traditional corks are made from the bark of cork oaks. This is stripped off and stacked on the forest floor where it leaches naturally with rain. It is then allowed to mature for 12 months and steamed to remove lignins and tannins which increases its elasticity. If traces of chlorine were present in the water, either in the rain or steam, there is a chance that minute quantities of Tri-Chloro Anisole (TCA) may form. It is this compound that causes “corked” wine.

How Serious Is The Problem?
Estimates indicate that 8-10% of all wines are affected to some degree. At one New Zealand tasting 36% of the Riesling samples were corked.

If One Bottle In A Case Is Corked Will The Rest Also Be Corked?
No. TCA infects corks indiscriminately so the defect is purely random.

Is “Corked” Wine Easy to Detect?
It depends. Some people can detect it more easily than others. There are also varying degrees of corkiness: a badly corked wine will have an obvious “musty” smell of damp cardboard while a less affected bottle will merely taste flat and lifeless. Corked bottles should always be replaced by your Wine Merchant. The main concern of many Winemakers & Merchants are those bottles where the fault is unidentified by the consumer, who merely concludes that they don’t like the wine and, quite reasonably, decides not to buy it again.

Can Corked Wine Be Prevented?
Yes. We know what the problem is and we know what causes it. Good quality corks and good hygiene during production go a long way towards eliminating the problem. However, the problem can be eliminated entirely by using a material other than cork.

Are There Any Environmental Issues Here?
Yes. A widespread switch away from cork would threaten the existence of the cork forests and the ecosystems that depend on them. Cork is also biodegradable whereas synthetic alternatives are not. Plastic corks could be recycled though. These are important considerations but the fact remains that without cork, there would be no corked wine.

Why Don’t All Producers Use Plastic Corks?
Many people recognise that there is a certain “theatre” involved with wine drinking. In the minds of traditionalists plastic will never take the place of real cork – it is difficult to imagine paying a lot of money for a top claret to then discover that it has a plastic cork. The jury is also still out on the long term effect on the ageing of wines with plastic corks. As with everything in life, you get what you pay for and, if a winemaker buys cork of sufficient quality to start with, he is arguably less susceptible to problems caused by TCA. The dangers of corked wine would appear to be greater where costs have had to be shaved and corners cut to achieve particular price points.

Is There Any Difference In The Types Of Plastic Corks?
Maybe. They are designed to be inert and seal the bottle efficiently. Some are made to look like real cork in an attempt to win over more traditional drinkers. We have seen wines that have black plastic corks in them – the Winemaker says this is a deliberate move to not try and hide the fact that the cork is plastic. Other Winemakers report some problems with plastic corks losing their elasticity over the long term and either letting air in (oxidising the wine), or not being able to get the cork out (almost too serious for words)! Plastic corks would appear to be best suited to wines intended for early drinking.

What Other Alternatives Are Available?
The screw-cap is increasingly used in its updated form, the “Stelvin“ closure. Its initial introduction in the 1970’s was a marketing disaster since, despite the capsules’ technical merits, the public perceived screw-capped wine as cheap and low quality. But this is changing. Many producers in Australia and New Zealand are now bottling their wines under “Stelvin” where it has been welcomed by a more informed and discerning public as a guarantee of fresh wine.

What’s Special About a Screw-Cap?
The aluminium capsule houses a liner/seal consisting of a layer of expanded polythene, a tin foil layer and a further thick layer that is in contact with the wine. The bottle is sealed by a tight compression of the seal liner against the mouth of the bottle.

How Will Wines With Screw-Caps Age?
Many of the wines bottled in the 1970’s experiment with screw-caps were still drinking beautifully over 30 years later, so the omens are good. However, most producers seem to be restricting their use of screw-caps to wines that are for early drinking where freshness is essential. It will be interesting to see if anybody is brave enough to bottle some big sturdy red that requires several years to age in screw-capped bottles.

What do Wines of Interest think?
Whilst we do not feel ready to consign the traditional cork to the spitoon of history, we do welcome the introduction of the screw-cap as a means of eliminating corked wines. Centuries ago cork was the most modern and innovative material with which to seal bottles of wine, and it is quite reasonable that in the 21st century more up to date alternatives are being tried.

Our experience in tasting samples indicates that screw-capped wines are always fresh and this is the most important thing. The bottles are also easy to re-seal if required. While many of the plastic corks come out easily some can be hard to get back in – the only solution to this is to finish the bottle of course!

We do acknowledge that there is a certain aesthetically pleasing quality to drawing a real cork, but do not anticipate that more modern closures will distract us, or our customers, from what really matters – the stuff that you drink!

Plastic corks seem good for wines that are intended for early drinking, where the loss of any elasticity in the seal is not an issue. However, given the recent developments in screw-cap technology, these would appear to be the way forward in the battle against corked wine. The only problem is convincing the Traditionalists!

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