Drink enough wine and you'll soon discover that wine is subject to faults that affect its taste. The most obvious of these are the bottle taint caused by a faulty cork and oxidisation which turns a white wine to an almost Madeira-like colour. Many other faults turn out to be benefits, depending on your point of view. Dom Perignon spent much of his time trying to cure the problem of secondary, or bottle fermentation. In the end though it was agreed that this fault in the wine could be quite attractive, and so the empire that is Champagne was born. So we could say that if the secondary fermentation is achieved on purpose, then it makes an expensive wine. If it happens by accident, then it's a fault.

It wouldn't be stretching credulity to suggest that for centuries wine-makers rejected the bunches of grapes on their vines in late autumn that had succumbed to to the fungus botrytis. A bunch of grapes that has been attacked by this fungus isn't an attractive sight. The grapes shrivel and grow a hairy fungal mould on their skins. But someone, somewhere looked at those grapes and thought 'I'll make some wine out those.' That's in the same league as the first person who opened an oyster, looked at it, and thought 'I'll eat that.' Of course we now know that wine made from botrytis grapes makes those wonderfully intense and heady dessert wines that cost so much. The shrivelling carries with it the benefit of concentrating the flavours to maximum effect.

Wine writers often write of 'volatile acidity', which like other faults need not always be harmful. Basically there are two chemicals in this category, acetic acid and ethyl acetate. Acetic acid is the taste we all know as vinegar and it can be present in small amounts, or in sufficiently large amounts that we call the liquid 'vinegar'. The ethyl acetate is the chemical that gives rise to that 'pear drops' smell, and in more exreme cases gives us the smell of nail-polish remover. With a hint of these volatile acids present, their quick evaporation brings with it other elements into the bouquet, an effect that's readily noticeable in a vintage port.

So when is a fault a fault? The simplest answer is to say that anything becomes a fault if it becomes noticeable. If its presence makes the enjoyment of the wine impossible, then it's a fault. Most of these chemicals are not simply there or not there, they're always present, but it's the quantity that determines our discernment of taste. A wine that's just begun its path to bottle taint might escape our notice, but one that's well down the road probably won't make it to our lips once it's been smelt.

Wine of the Week

Le Jaja de Jau Rose 2002

Jaja is local French patois for quaffing wine, and this quaffing wine comes from Chateau de Jau in the Rousillon. It's funky label design is determinedly unpretentious as is the wine inside the bottle. The rose has a very dry finish, with some fruity overtones. A perfect sunny afternoon wine.
Available from Bubble Brothers Cork, €9.95