Gnomon's Guide

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.

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 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 stripped off.

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. Layering of the cork is done for extra strength. The cork is compressed laterally before being inserted into the bottle and it retains some of this when it is removed, giving the familiar mushroom shape.

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 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 knows how it gets there. 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. 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.

Obviously, this is a major problem for wine manufacturers, since they must bear the cost of 8% of their wine being undrinkable.

Plastic corks

The solution to the problem of corked wine is to use corks made of plastic. These are becoming increasingly popular with wine manufacturers, since they do not suffer from the problem of TCA. Unfortunately, they have a very negative image with the wine-buying public. A good wine is a treat for which you pay a good price. People like the idea of tradition when buying a good wine - the image of an old man caring for his vats of wine is a common one in advertising. Plastic corks suggest cheap mass production in steel drums, which puts people off. But wines with plastic corks are in fact more likely to be drinkable. It will be a while yet before the plastic cork is accepted.

A few points against plastic corks:

• 'Wine experts' claim that the plastic cork imparts a very slight plastic taste to the wine, which they can detect. If you are someone who worries more about gooseberries and cat-pee than about grapes, then you may be put off by this, but for the rest of us, the effect is unnoticeable.
• Corks made of cork are better for the environment. They are made from a natural substance which will degrade with time, while the plastic corks will probably lie in rubbish dumps for millennia.
• The cork forests of Portugal are the home to many species of bird. These forests will be cut down if production of cork ceases. This particular argument against plastic corks has the distinctive sound of scraping the bottom of the barrel by the anti-plastic lobby.
• They make a 'quacking noise' when they come out of the bottle. More bottom-scraping.

Things to do with a cork

Gardening

Many people each year injure their eyes while gardening. They place sticks and canes into the ground, and later poke their eyes on the sticks, because they don't see them. Ouch! It is highly recommended that you put a cork on the top of each stick, ideally a sparkling wine cork. You will then notice the stick, and even if you do hit your eye on it, it is unlikely to do any damage.

Stick figure animals

Amusing stick figure animals can be made from corks and cocktail sticks¹. Use corks for the body and head, use cocktail sticks for the legs, neck, tail etc.

Toy boats

Since corks float, you can make little toy boats from them. Cut the cork in half lengthways. Insert a long screw into the curved side to act as a keel. The weight of this will keep the cork upright. Add a sail using a cocktail stick and a piece of paper.

The Two Corks Trick

This piece of sleight of hand is hard to describe, but if you persevere with these instructions, you can really impress or bore your friends, depending on your skill and panache. All you need is two corks.

Place a cork in each hand in the crook between thumb and hand. Grasp the ends of each cork with the thumb and index finger of the opposite hand. Pull your hands apart. The two corks will collide, as you would expect.

Now repeat the process, but with a slight difference. Hold the corks between thumb and hand as before. Turn your left hand palm downwards, your right hand palm upwards. Place each thumb on the end of the cork in the other hand. Bend each index finger around the thumb of the other hand so that it touches the other end of the cork. You are now holding the two corks between thumb and index finger. Pull your hands apart. The two corks should come out cleanly, leaving you with a cork in each hand. Impressive!

With practice you can perform this trick without turning your hands very much, so it is not at all obvious what you are doing. Most people are unable to understand it even when it is done right in front of them in slow motion!

Disposing of blades

If you are throwing out an old blade such as a razor blade or the blade of a Stanley knife, you can push it into a cork first, to make it safe. This means you won't slice yourself open later when pushing more rubbish into the bin.

Burnt cork

Burnt cork makes an excellent black substance which can be used for painting false mustaches on yourself and your friends. You'll be in good company, along with Groucho Marx, that eminent comedian who went through life wearing a painted-on mustache.

Door stoppers

A cork can make a fine impromptu door-stopper.

Hats

You can hang corks from the brim of your hat to keep the flies off. This is likely to make you look like a prat in a hat, unless you really are an Australian.

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