Anybody who drinks wine is familiar with the popping sound of a cork being removed.
Corks are those cylindrical things which keep the wine in the bottle. However, most of us don't give a moment to consider where those little corks come from or why we use them.
Where Do Corks Come from?
There are two types of cork: the new-fangled plastic variety and the traditional one made from that spongy stuff known as cork. Cork is actually the bark of a tree called the cork oak (Quercus suber). These grow in plantations, mainly in Portugal and Spain. The bark is stripped off the tree and used to make the corks. This does not damage the tree, as it regrows new bark. After nine years, it has recovered enough to be stripped again. A mature tree can produce 200kg of cork every nine years for as long as 200 years. The trees are so accustomed to having their bark stripped that they have serious problems if the bark is not removed.
Normal corks are just cylinders cut from the bark. Sparkling wine corks are much more complicated. They have to be much stronger so that they can withstand the pressure of all those bubbles. They are also cylinders, but much wider and the cork is layered to provide extra strength. The cork is compressed laterally before being inserted into the bottle, but it retains a sense of its original shape, apparent in the familiar mushroom shaped heads of such corks.
How Do Corks Work?
Natural cork is a material with an unusual property: it does not expand laterally when it is compressed. This means that a cork stays more or less the same width when it is squashed lengthways, making it possible to push it into the bottle neck. Most materials swell outwards as they are compressed, so they would jam in the neck. There's just enough outward expansion in a cork to make a good seal. Technically speaking, cork has a Poisson's Ratio very close to zero, which is just a more obtuse, scientific way of saying the same thing.
Corked Wine
Although corks made of cork are considered the sign of traditional values and quality, they have a major problem. About 5-8% of wine bottles are tainted with a chemical called trichloroanisole (TCA for short). This comes from the cork, but nobody seems to have a definitive conclusion as to why this taint comes about . Such wine is known as 'corked'. In small amounts, it can make the wine taste flat and flavourless. In larger amounts, it has an obnoxious musty taste likened to wet carpets, which makes the wine undrinkable. Obviously, this is a major problem for wine manufacturers, since they must bear the cost of 8% of their wine being undrinkable.
Corked wine is the reason for the little ritual in restaurants, where one person is asked to taste the wine. Don't worry, if the wine is corked, you will know! Send it back and get another.
