What is "corked" wine?
A "corked" wine is one that has been spoiled by a cork contaminated by "Trichloranisole", or TCA, which can be detected at concentrations of just a few parts per trillion. It affects the wine, giving it a musty, dank, mouldy smell and an off taste. Chlorine solutions used to sterilise corks have been found to encourage the production of TCA. This is the most common wine fault and can occur at the rate of one in 20 bottles opened (not at such a high rate for fine wines). This has stimulated the development of stoppers made from types of plastic, agglomerate cork and even screw tops. Cork floating in the wine does not mean it is corked. It is a sign of a dried out cork or it could simply be that the bottle has been opened poorly. Mould on top of the cork is nothing to worry about either.
How do you tell if a wine is too old to drink?
Contact with air, or "oxidisation", spoils wine and is caused when a wine has been open for too long, has an ill-fitting cork or is simply too old. It is easy to spot; on the nose the wine will have a sherry-like smell and will taste dull and lifeless. Red wines will be dull brown in colour, and White wines will turn a tawny or brown colour. Opened bottles of wine have a very limited life span. See Drinking Wine for information about how long you should keep opened bottles of wine.
Are the crystals found in some wines harmful?
You will quite often spot clear crystals that look rather like sugar in the bottom of a bottle or glass. Sometimes the crystals attach themselves to the cork if the bottle has been stored on its side. They are "Tartaric Acid Crystals" (also known as "Tartrates") and are neither harmful to the drinker or the wine. Tartaric Acid is a natural component found in grapes, and therefore wine, that crystallises when wine becomes very cold, or if the wine is old. Tartrates are usually a sign of a quality wine that has not been over-treated during vinification. It is possible to ensure that the Tartrates do not form by filtering the wine prior to bottling. However such aggressive filtration is a more common practice in the making of bulk-produced wines because it can also strip a wine of its flavour.
What does it mean when a still wine is cloudy or fizzy?
Cloudiness usually indicates the growth of yeast or bacteria; fizziness that the wine has undergone an unintentional second fermentation in its bottle. Both of these are definitely faults, often due to bad winemaking. It is likely the wine will be unpleasant, albeit harmless, to drink.
What is wrong with a wine that smells and tastes of vinegar?
The smell and/or taste of vinegar indicates that a wine has either been badly made or the bottle has been open for too long and has been attacked by a bacteria, called "Acetobacter". Acetobacter reacts with oxygen and this reaction changes the taste of a wine to a vinegary flavour. In fact, this is how vinegar is made. This fault is also described as "volatile".
Why do some wines smell of "struck matches"?
Sulphur Dioxide (SO2) is the most common chemical used in winemaking. Almost every wine is made using this compound because it helps prevent oxidisation and stabilises wine. Careful winemakers use it judiciously because excessive amounts of SO2 causes disagreeable aromas in the wine. Within the EU there are maximum permitted levels that may be used. SO2 is detected by a smell reminiscent to struck matches or bad eggs and may cause an unpleasant tingling sensation in the nose. However these wines will not be harmful, just unpleasant.