Cork taint is the most common problem with wine, but sometimes other things go wrong. This usually means one of two things. Either the wine has ‘cooked’ through exposure to excessive heat, or it has oxidised prematurely. If either of these things happen, the wine may turn brown and taste sour, excessively ‘stewed’, or even of vinegar. However, not all wines that taste oxidised or cooked are faulty. Traditional white Rioja, Sherry, Madeira and many natural wines (to name just a few examples) are deliberately oxidised, heated or made without preservatives, specifically to produce an unusual flavour. Like the mould in a blue cheese, this is an integral part of the wine’s character. Similarly, as a wine ages it slowly oxidises. An old wine that is past its peak may taste tired, but it is not faulty. A wine is only faulty when the ‘fault’ causes it not to taste as it should, given its style and age.