Corked wine is the bain of the wine drinker. The wine smells of damp cardboard, and will often lose some or all fruit character. The intensity varies, at times only a lack of fruit can give it away and it can go unnoticed. Other times the damp cardboard / musty aroma can put off even the most inexperienced drinker.
The aroma is caused by the presence of the chemical 2,4,6 trichloroanisole, (or TCA for short). The exact number of Corked (or TCA tainted) bottles of wine ranges between 5 and 8% as measured in large competitions such as the International Wine Challenge.
The chemicals that cause it (often called precursors) are found in the bark of the tree, and more likely to be close to the ground. Some cork producers discard the bottom 10-12.5cm of the cork oak tree (a member of the Beech family). Drying now also occurs on concrete keeping the cork away from the soil, concrete is the greatest preventative measure against TCA according to Carlos de Jesus, of Amorim which has 25% of the global cork market. Cross infection is minimised by removing all wood to store and transport, such as pallets. The cork is then boiled to drive out any TCA. Other improvement has been to stop using chlorine to clean the cork, as TCA likes the presence of Chlorine. Amorim, who now have the equipment to measure TCA (with Gas Chromatography- mass spectrometry) consider that these new measures have improved TCA incident's by 80%.
Diam, another leading cork manufacturer has taken a different approach. Cork granules are cleaned by super critical carbon dioxide. Super critical means that carbon dioxide is held in a state of both a gas and a liquid. In this state it becomes a brilliant solvent cleaning out the TCA from the cork. Diam claim a 98% efficiency which has been backed by the Australian Wine Research Institute. This technology has been around for 20 years and is used to remove caffeine for high quality de-caffeinated coffee.
The work of removing TCA is not always 100%, however if the amount of TCA is reduced then it may exist in undetectable levels in many wines and simply dulls the fruit flavours. Our noses detect TCA at a certain trigger level, which means it can be present we are just not aware of it. But once that trigger level is reached we become acutely aware of the off-smell.