More Than Just A Stopper In A Bottle
The Age
Monday September 18, 1995
A CORK is just a stopper to most people. You take your corkscrew and pull it out to get at the good stuff inside the bottle.
But a cork is much more important than most people realise: a good cork can protect a treasured wine for many years, while a bad one can ruin even the highest-quality wine.
The value of cork as a seal for wine bottles was first realised in the late 17th century. Before this, wine spent most of its life in the barrel. The discovery of the cork meant bottles could be sealed tight and, for the first time, people came to appreciate the desirable qualities bottle age could impart to their wine. This discovery also meant wine could be more easily transported and readily stored in small quantities.
Corks are made from the bark of a type of oak that grows around the Mediterranean, particularly in Portugal, where the main cork industry has been located for centuries. Cork oak trees reach maturity at about 25 years, but take about twice that long to produce cork of commercial quality. The cork used is that which grows back after the original bark has been stripped. This regrown bark is then taken off the tree every nine years.
After harvesting, the bark is stacked in the forest for a year prior to being classed for quality. It is then boiled and flattened into long strips from which the corks are punched.
The corks are then bleached and disinfected in a series of processes, including washing with chlorine. Drying, classifying into three grades, packing and distribution follow.
Once in the bottle, a good-quality cork can usually be relied on to provide a good seal for many years. But the wine must be stored laying on its side so the porous cork is swollen by contact with the liquid. If a wine bottle is kept standing up, the cork will dry out and shrink, allowing in air that will spoil the contents.
If you are cellaring wine for any length of time, it is a good idea to inspect the plastic, foil or metal capsule covering the cork from time to time. Look for wine weeping out underneath it or a bulge at the end, which indicates that there is a problem with the cork's sealing properties. Similarly, when buying wine it is worthwhile checking for telltale signs that the cork isn't doing its job.
As wine ages, the cork allows some interplay between the wine sealed inside the bottle and the air outside. Variations in temperature exacerbate this. In warm weather the wine inside expands and tiny amounts of wine seep past the cork and evaporate; in the cooler months the wine contracts a little, allowing in a small amount of air. This is why a constant storage temperature is important for wine. Dramatic fluctuations or too much heat cause oxidation and greatly accelerate ageing in wine, which does not allow complexities of flavor to develop. A sure sign that a wine has been subjected to excessive heat is a cork projecting well beyond the top of the bottle neck, coupled with a lot of sticky residue around the cork end.
Unfortunately, the quality of corks used by many wineries in Australia leaves a lot to be desired. There is no comparison, for instance, between the quality of the cork used in a good French Bordeaux red, for example, and that in a local cabernet.
Good corks are firm-textured, whereas poor ones are very porous and can lead to sealing problems.
Many of the cheap corks tend to be ``agglomerates", made up of cork fragments bonded into a single cylinder. These are usually found only in wines made for early consumption, not the finest bottles.
Eventually even tiny losses of wine past the cork add up, with the result that older wines often have a greater ullage (the air space between the surface of the wine and the end of the cork) than young. Beware of too much ullage in younger wines as this usually means the wines will be in poor condition.
As a rough guide, the further the wine is up the neck of the bottle, the better. If the wine is below the bottom of the neck, you may have a problem. In older wines, say a 20- year-old bottle, wine at the bottom of the neck is much less cause for concern. If you have several older bottles and the level is any lower than the bottom of the neck, it is worth tasting a bottle to make sure it is sound. Remember, corks lose a lot of their elasticity as they grow old. If you want to keep the wine for many more years, it may be worth re-corking each bottle. Seek advice from a home-bottling expert or a good wine merchant before you start as it can be a risky procedure.
A problem with corks that has beome the bane of the wine industry is ``cork taint", which results in a wine tasting ``corked". A corked wine smells of wet cardboard or mouldy cork. At worst, the wine is rank and totally undrinkable. When very slight, cork taint is only detectable with experience.
To most people, slightly corked wine just seems a bit flat in aroma and flavor. The causes of cork taint are complex, but the main culprit seems to be an intensely smelly compound known as 2,4,6 trichloroanisole or TCA. Professor Terry Lee, the director of the Australian Wine Research Institute in South Australia, says the two main contributors to the formation of TCA are mould growth and chlorine. Other sources of TCA can be wooden containers used to ship corks or even the water used to wash them.
The incidence of cork-tainted wine is significant in Australia.
the Uncorked tastings by The Age indicate an incidence of two to five per cent.
© 1995 The Age
