Some minor changes in the condition of a wine are of a nature that do not detract from the aroma or flavour. The most common example is the precipitation of tart rates, yeasts or colouring substances which form a sediment
in the bottom of the bottle. More serious defects due to contamination alter the taste and odour. The most common are: 

	Taste/smell of cork: a mouldy smell of mushrooms or damp earth caused by corks made from raw material infected by a parasitic fungus, Armillaria Mellea. Another source of contamination is a mould which can form under the corks of bottles left standing upright and which has a smell reminiscent of wet cardboard. It can be avoided by storing bottles horizontally so the wine is always in contact with the bottom of the cork.
	Taste/smell of dry wood: is the result of the neglect of barrel hygiene. Left empty without cleaning with sulphur, barrels may transmit odours of dry wood and astringent flavours to wine aged in them.
	Smell of sulphur: an acrid odour similar to that of a struck match, caused by the excessive use of s ulphur dioxide. Also leaves a bitter, prickly sensation at the back of the throat.
	Oxidation: is a serious defect which mainly affects dry white wines. Also known as maderization. Oxidized wines have an unhealthy dark and lifeless colour and an unpleasant odour like burnt caramel.