Tuesday, January 01, 2008

To Screw or Not to Screw

There is a misconception in many wine consuming countries that a bottle closed with a screw cap indicates cheap wine. While this may have been true when the screw cap first made its appearance back in the 1970's, nothing could be further from the truth now.
But why would you need to replace cork as a closure for a wine bottle?.
The answer is simple.
Trichloroanisole or TCA, commonly known as cork taint or "corking".
Contamination by this compound leaves the wine tasting musty and dull. It is formed when chlorine used for bleaching reacts with mould already growing in the cork. The average wine drinker is sensitive to the compound and can detect it even at dilutions of six parts per trillion. TCA can occur in several areas of a bottling facility, such as drains and barrels, but corks pose the biggest problem.
It is believed that up to 10% of the world's wine is affected.

The cork industry has failed to address this problem satisfactorily and the search for alternative closures has been initiated.
One answer has been the synthetic ‘cork’, which is already widely used. But some wine tasters complain of ‘plastic taint’ and many consumers find them difficult to remove from the bottle.
The screw cap concept of the 70's has been developed further. The capsule system is made up of a screw cap, a long printable skirt and a liner specifically designed for contact with wine. The glass bottle used with the system has a screw thread beginning at 2.8mm below the neck top and the closure is re-drawn to avoid leakage.
Two types of liner give an element of control over the desired permeability of the seal. The Saranex liner is made from layers of polyethylene, PVDC (polyvinylidene chloride) and expanded polyethylene, whereas the Saran film etain has a layer of tin sandwiched between PVDC, white kraft and expanded polyethylene. This tin layer means that it is much less permeable than the Saranex liner and less oxygen is allowed to enter the bottle.
Wine companies tend to use the Saran film etain liner for wines stored for longer periods of up to 10 years, with the Saranex intended for storage of between two and five years.
It is clear that white wine sealed by a screw cap is protected from oxidation and the threat of cork taint. Comparative tastings of the same white wines under cork and screw cap have shown the latter to be fresher and more consistent.

The question of ageing of red wines under screw cap is one that is regularly raised.
There is a school of thought that minute quantities of oxygen leeching into the wine over years through a cork contributes greatly to the ageing properties of the wine.
Another school thinks that it is the oxygen already in the wine that aids ageing and that any oxygen ingress from outside leads to premature oxidation. It has also been suggested that much of the ageing process takes place anerobically.
Thus it is surmised that a red wine under a screw cap will age at the same rate as a one under a perfectly corked one.........without the threat of "corking".
Because so little premium red wine has been sealed under screw cap so far, practical results are not yet available.
But more and more are becoming available, particularly in Australia and New Zealand, so it is obvious that the wine industries in those countries have full confidence in the screw cap closure.

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