The problem with cork.
Sadly, there has been many a great wine ruined by cork taint. Most well informed sources agree that at least three percent of wine is affected – probably more. Cork taint, a problem commonly caused by a compound known as TCA (its chemical name is 2, 4, 6 trichloroanisole) is produced by a fungus in the cork developing inside the closure and infusing the wine with a smell that many describe as similar to the smell of wet cardboard and can destroy the taste and aroma of the wine. An equally serious issue for a wine is the potential for 'random oxidation' due to the inherent variability of cork’s oxygen barrier. On the other hand when storing wines under screw cap, the food-grade polymer seal in the cap can virtually eliminate outside air contact, preventing not only leakage but eliminating spoilage due to cork taint.
Effects on ageing.
Storing wines under screw cap, still allows wines to develop and the flavours mature, though many believe it will be at a slower, more controlled rate. Wines age as a result of not only that small amount of air that enters the bottle through the cork. Many of the changes in a wine occur without the presence of oxygen, so will continue unaffected. This in turn means there will be far less variation in wine quality from one bottle to another. Storing wines under a screwcap means you can leave them standing upright or lying down. Normally the only reason to lay bottles down is to keep the cork from drying out. So storing wines under screw cap can offer greater flexibility in where and how you locate your cellar.