Cork
The material we call cork is simply the thick outer bark of the cork oak, Quercus velaris. Light and springy, it repels water, resists heat and flame, and serves an enormous variety of uses. People have relied on it for thousands of years: Phoenician traders pressed slabs of it into their storage jars to keep the contents dry, while later Mediterranean peoples shaped it into everything from net floats to shoe soles.
The tree that yields it is no less extraordinary. A cork oak's bark can reach thirty centimetres in depth, and, wrapping the trunk and branches like a heavy coat, it holds the interior at a steady eighteen degrees Celsius whatever the season. This protective layer most likely evolved to shield the tree from forest fires, and it owes its qualities to an unusual cellular make-up – close to sixty million tiny cells in every cubic centimetre – that no laboratory has so far managed to reproduce. Each of those cells is packed with gas rather than liquid, which lets cork float so readily. The same structure lends it a springiness: crush a piece, release it, and it recovers its original shape at once.
A scattering of warm-climate countries is home to the cork oak – among them Algeria, Tunisia, Sardinia, southern France and parts of Anatolia. What the tree asks for is a mild, sunny setting whose yearly rainfall runs to at least five hundred millimetres yet stays below nine hundred. Poor ground suits it well; much as grape vines do, it drives its roots deep in the hunt for water and nourishment. Because every one of these conditions is met in the Sendra highlands of southern Sardinia, that district had become the world's foremost source of cork by the 1920s, and even now supplies close to forty-five percent of the global total.
The cork forests tend to stay in family hands, and a good many of these enterprises – like a good many of the trees – have stood for well over a century and a half. If anything is learned from cork-growing, it is patience. Thirty years will pass before a newly planted sapling gives its first harvest, and, once a tree is in production, no fewer than nine years must separate one stripping from the next. Cork of the very highest grade asks longer still – another two decades or so. Even the choice of day matters: should the bark be taken when the weather has turned cold, or when the air hangs damp, the tree is left the worse for it.
Harvesting is skilled work of a very particular sort. Because no machine has ever been devised for stripping the bark, the task falls to teams of seasoned labourers. Small, sharp axes in hand, they cut downward through the bark and then prise it off in the largest pieces they can lift; the ablest of them can free a single curved slab that runs the whole length of the trunk, from close to the ground up to the lowest branches. For roughly six months the bark is left to dry in the open, after which it travels to the factories to be boiled – a step that kills off any insects still lodged within. Around seventy percent of what emerges becomes the familiar bottle stopper, while most of the rest is claimed by the building trade, serving as board and tiles that deaden heat and noise, or granules stirred into concrete.
Cork's near-total grip on the bottle-stopper market has slipped in recent times, the worry being what it can do to whatever a bottle holds. Behind the trouble lies a compound the trade calls trichlorocresyl ether, which appears when plant phenols, chlorine and mould react with one another. Quantities almost too small to picture – no more than five parts in a trillion – are already enough to ruin the flavour of the drink inside. Little by little, then, producers have shifted first to plastic stoppers and, more lately, to aluminium screw caps. Alternatives of this kind are inexpensive to manufacture, and a screw cap, at least, is a good deal simpler for the buyer to use.
For all that, a great deal can still be said for the classic cork stopper. Its familiar look sits easily alongside the reputation of the premium products it has long been tied to. More telling still, cork is a renewable material, one that can be reused without the slightest trouble. The forests, besides, are an asset in themselves: they sustain the local wildlife and hold erosion in check across the districts where they grow. And so, with public attention now fixed firmly on the environment, the prospects for this age-old material look bright once more.
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Question 1 - 5
Choose TRUE/FALSE/NOT GIVEN
1.
In ancient times, cork was used to protect stored goods from damp.
True
False
Not given
2.
Scientists have produced a man-made material that copies the way cork's cells are arranged.
True
False
Not given
3.
Cork oaks require more rainfall than vines do.
True
False
Not given
4.
Bark should be removed from the tree only in dry weather.
True
False
Not given
5.
The bark of cork oaks is now stripped by machine.
True
False
Not given