Screwcap or Cork?

Louis Pasteur once described oxygen as “the enemy of wine”.

The problem with cork is oxidation; where the cork simply hasn’t done its job of keeping the air out. A bad cork combined with variations in storage temperatures means the contraction and expansion of the wine will draw oxygen through into the wine. The most damaging temperature changes are those recorded daily, although seasonal changes can also damage the wine.

This stems from the fact that not only are no two corks the same, but also no two bottle necks are the same either. Therefore some corks in some bottles will withstand the hydraulic pressure increases when the wine warms and some will eventually succumb, allowing air (oxygen) into the bottle as well as the escape of remnant sulphur dioxide.

The other “interesting” effect with corked bottles is a loss of wine volume, sometimes referred to as the “angel’s share” (technical term “ullage”).   A volume of the wine itself will slowly be lost as the wine expands and contracts, and a substantial air space will start to develop.

Of all the 6827 wines detailed in James Halliday’s 2012 Wine Companion, reported that 85% used screw caps. Even more telling was that 97% of white table wines were screw capped. The battle in Australia has largely been fought and won by the screw cap - but other parts of the world are clearly not as innovative as Australia and still favour cork.

Screw caps are great at preventing or at least slowing the more obvious changes in wine as it ages. Colour development in all the bottles stored alongside each other will be identical, and there is no wine given up to the angels. Most of the good changes a wine goes through over time are anaerobic (they don’t depend on a constant supply of oxygen – something that screw caps are very good at stopping.

Interestingly wine makers have also experimented with plastic corks, but these failed to keep the oxidation at bay for any real length of time and should be avoided.

So there you go – given a choice between screw cap and cork you should favour the screw cap wherever you can.

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