The time-honoured way of sealing bottles is with a cork. Cork is remarkable, It’s got a bit of give, it’s mostly waterproof, and has insulating properties. It’s also used in floor tiles, insulated table mats, the cores of cricket balls and even the soles of shoes.
Botanist, Dr Peter Valder explains more about this fascinating tree.
Where does cork come from?
Cork is the bark of a tree called the cork oak, Quercus suber. “Quercus” is what the Romans called oak trees and “suber” is what they called cork. It’s a native of the Mediterranean region with Portugal producing the most cork. It’s an evergreen tree, and perhaps not what you would expect an oak tree to look like. If you look amongst the leaves, you can see the yellow male catkins that produce the pollen, that fertilizes the inconspicuous female flowers that develop into the acorns, which fall to the ground.
How is cork harvested?
Breaking a small piece of bark from the Cork oak will reveal recognisable cork. Cork harvesters cut right round the tree horizontally at the bottom and at again at about two metres up the trunk. Then they make two vertical cuts on opposite sides of the truck, so that they can peel the two halves off yielding a nice, thick layer of cork. This does not ring bark the tree, however, it takes eight to ten years for it to grow back and be thick enough to be worth harvesting again. (Ring barking is a process that can kill trees or hinder growth above the ring barking point).
Can you grow your own cork tree?
Cork trees are a lovely tree to have in bigger backyard as well as being somewhat of a curio. Cork Trees are evergreen and grow up to 15-20meters tall and equally as wide, making them wonderful shade trees that are best suited to rural gardens. They require a full sun position, are very hardy once established and will grow in the cool, temperate and the warmer temperate areas of Australia. They are available from specialist growers.
How is cork used in wine and champagne bottles?
With the wine industry booming in Australia, California, South Africa, Chile, and everywhere else, it’s getting hard to find enough cork thick enough to cut solid corks from. Consequently, many corks these days are made from granular cork, often with a disc of solid cork on either end. More commonly these days, wine bottles have metal screw top seals instead of a cork. Most champagne corks are reconstituted. The upper swollen part is made of reconstituted granulated cork and there are a couple of discs on either end.
Why should wine bottles should be kept on their side?
Because if you leave them upright, the cork may partially dry out and shrink, letting air in, enabling the bacteria that can convert alcohol to vinegar to grow and spoil the wine. But if you leave it lying on its side, the cork is kept wet, and the air can’t get in, and the bacteria can’t grow. Like us, bacteria need oxygen to be able to get on with the job.
