A wine is corked when it has been in contact with a cork infected with a fungus that produces trichloroanisole, otherwise known as TCA. It is this chemical, rather than the fungus itself, that imparts the unpalatable flavours to the wine. Cork taint spoils up to 5% of all bottles of wine. Screw caps have gone some way to alleviating this problem. A corked wine is not one with bits of cork in it, corked wine may appear fruitless, a little unbalanced, uninteresting, but without any definite signs of cork taint. More obviously corked wine has aromas of wet cardboard, mushrooms or mould.
When a wine is exposed to high temperatures, the liquid expands and several things can happen. It may force the cork from the neck of the bottle, pushing it up under the capsule. Or the wine may expand and leak around the cork. In either case, when the liquid cools it will contract, and this may result in air seeping in around the cork leading to a further problem, oxidation. Cooked wines won't have any freshness to the fruit aromas or flavours - instead you'll get a stewed, prune-like profile. If you're getting blackcurrants and fresh summer fruits, for example, then you haven't got a cooked wine. On the palate, the wine often seems thin, lacking body and character.
Oxygen is important in the development of wine. The interaction between the wine and the small amount of air behind the cork, over many years, is one of ways wine develops in the bottle. It may even involve minuscule amounts of air seeping past the cork over time. Should the wine come into free contact with oxygen, however, whether during careless winemaking, or due to a faulty cork, oxidation will rapidly ruin the wine. Oxygen is an aggressive element, and will interact with most substances, resulting in their degradation. Fruitless wines with a flavour resembling old and worn out Madeira or Sherry may well be oxidised.
A commonly used preservative, the addition of sulphur dioxide is practiced by manywinemakers. It can help stabilise the wine during and after the winemaking process. An excessive amount of sulphur will produce fairly characteristic aromas and flavours, giving a wine that reminds you of mothballs, burnt matches or burnt rubber.
Sediments and Crystals
Neither of these are true faults, but both have the potential to spoil the experience unless they are understood. Sedimentation in the bottle is a natural occurrence in many wines, generally those designed to withstand some ageing, and it simply reflects the solid matter settling out of the wine. These wines should be decanted (see our founder, John Frazier show you how).
The most common crystals found in wine are tartrate crystals, and these are often found on the underside of the cork, or in free suspension. Wines that have been cold-stabilised by the winemaker have been chilled in order to bring these crystals out of solution so that they can be removed. If this is not done, they may form later in the bottle, especially if kept in a cold cellar. They are of no concern, although they are again unpleasant if taken into the mouth, particularly if large when they may be mistaken for shards of glass.