Common Wine Faults
If you discover one of these faults we recommend that you replace the cork or screwcap and take it back the place where you purchased it. Particularly in restaurants, you should get a full refund or at least a replacement. They recognise that faulty wine is a fact of life and are nearly always happy to replace the wine. If the sommelier recommends that you try a different wine, take his suggestion. He is politely trying to tell you one of two things: either he considers the wine to be past its best and a new bottle will make little difference or he thinks it is fine and you just do not like it!
Heat damaged wines are often casually referred to as cooked, which suggests how heat can affect a wine. Bottles in storage should be cool to the touch, but not cold: a "cellar temperature" of 15 to 18 degrees C is ideal. Heat damaged wines often become oxidised, and red wines may take on a brick colour.
Cork taint or Corked Wine
Cork taint is the most common fault associated with wine. As it can only occur when cork is used it is becoming less frequent due to recent preference for screwcaps. The cause of cork taint is the presence of 2,4,6-trichloroanisole (TCA) in the wine. Most TCA is produced when naturally-occurring airborne fungi are presented with chlorophenol compounds, which then convert into chloroanisole. Chlorphenols can be a product of the chlorine bleaching process ironically used to sterilise corks, which has led to the increasing adoption of methods such as peroxide bleaching. To recognise it you should expect to smell a damp mustiness rather like the mould on old bread or a wet dog. Sometimes the cork taint is more prevalent when the wine is tasted rather than smelt. A very tainted wine is completely undrinkable - although harmless. Opinions differ on how often cork taint appears but the consensus seems to be that it occurs in 3-10% of bottles.
This is where air has got into the bottle via a faulty seal or where the bottle has been left open for too long. It sometimes occurs where the wine was not correctly protected from exposure to the air when it was made. Whatever the reason, the wine usually has a slightly metallic nose and tastes flat, tired and insipid. Affected white wines also tend to have a rather golden colour.
Refermentation is caused by yeasts refermenting the residual sugar present within bottled wine. The wine style "vinhos verdes" relies on this secondary fermentation in bottle to impart a slight spritziness to the wine.
Happens where the sulphur dioxide, used to protect the wine from oxidation during its making, bonds with hydrogen to create hydrogen sulphide. This is immediately apparent when the wine is opened as there will be an unmistakeable aroma of sulphur or rotten eggs. Leave the wine to breathe for 10-15 minutes as the smell often dissipates and you are left with a perfectly drinkable and pleasant wine.
See also Preservatives in wine
Evident when you get a mass of blackish crystals in the last glass poured from the bottle. This is a result of the wine not being fully stabilised before bottling. It does not affect the taste of the wine and the crystals are harmless. In fact, this can be a sign that the wine was hand made without too many chemicals processes being involved. Decant the wine carefully before drinking, leaving the final residue in the bottle.