A fault is an unpleasant characteristic in a wine resulting from poor manufacturing or storage conditions. Faults can be found in all wine and it is only when they become concentrated that they become noticeable. When the fault becomes the major characteristic of the wine, its quality is reduced and it may even become undrinkable.
Wine faults have many causes, ranging from poor hygiene in the winery, oxidisation (coming into contact with oxygen), contact with sulphur dioxide (or sulphites), winemaking errors, poor quality bottle closures to name a few.
Storage will also affect a wine’s quality, as they can be damaged by extremes of temperature and excessive exposure to light.
Below are the main faults:
Cork taint creates mouldy, musty and earthy aromas that hide the natural fruits. It is a attributed to the compound trichloroanisole (TCA), which originates as a mould on wine corks and barrels. Wines in this state are usually described as ‘corked’. As cork taint has such an infamous reputation, it is often blamed where other faults might be the problem. It is though that approximately 5% of all wines that are closed with a cork suffer this problem.
Sulphur dioxide occurs naturally in wine but in minute amounts, it is also added to prevent oxidation, bacteria damage and in winery sterilisation. Wine with too much sulphur dioxide (sulphitic wine) can taste of matchsticks, burnt rubber, or mothballs.
The oxidation of wine is perhaps the most common of wine faults. Oxidation can occur throughout the winemaking process, and even after the wine has been bottled. When a wine has become oxidised it leads to a loss of colour, flavour and aroma. Sulphur dioxide is used to prevent oxidisation but at the risk of producing the above fault.
Heat damaged wines are often casually referred to as cooked, which suggests how heat can affect a wine. The ideal storage temperature for wine is generally accepted to be 13°C (55°F). Wines that are stored at temperatures greatly higher than this will experience an increased aging rate and may even leak from the bottle. If a track of wine is visible along the length of the cork when opening a bottle of wine, the cork is partially pushed out of the bottle, or wine is visible on the top of the cork while it is still in the bottle, it has most likely been heat damaged. Heat damaged wines often become oxidised, and red wines may take on a brick colour.
Even if the temperatures do not reach extremes, temperature variation alone can allow the wine to become oxidised. All corks allow some leakage of air (hence old wines become increasingly oxidised), and temperature fluctuations will vary the pressure differential between the inside and outside of the bottle and will act to “pump” air into the bottle at a faster rate than will occur at a strictly maintained temperature.
Reputedly, heat damage is the most widespread and common problem found in wines. It often goes unnoticed because of the prevalence of the problem, consumers aren’t aware of the issue, and most would just chalk the problem to poor quality or other factors.
The following are not wine faults, they are prevalent in wine but are natural and do not harm the wine in any way.
In most cases sediment in bottled wine is a side effect of aging. It can mean that the wine hasn’t been filtered or fined before bottling. Many people believe this is positive as the formation of sediment is a naturally occurring process and filtration is said to remove flavour. Although the deposit is a downside to not filtering, the upsides include more flavour, more potential to develop a bouquet and increased ageability.
During fermentation, tartaric acid can react with potassium and be converted into potassium hydrogen tartrate. This compound may crystallise, when conditions are cold, to form small crystals in the wine. These are small, clear or white crystals. The crystals themselves are harmless and natural so the decision is a matter of appearance.
Cork comes from the bark of the cork oak, most of which is harvested in Portugal. Its elasticity and impermeability make it an ideal seal for bottles of wine, cork is also highly buoyant and fire resistance. Although cork has been used to seal wine for generations, it can sometimes adversely affect the wine with ‘cork taint’.
Screw caps (sometimes known as Stelvin caps) are more popular now. Made from aluminium, they thread onto the bottleneck and are generally thought to form a tighter seal and reduce the incidence of cork taint. There is still some disagreement about whether wine ages as well with screw caps as it does with cork.
Synthetic corks are also meant to reduce the risk of cork taint, while still looking and feeling like traditional corks. Unfortunately, some of these artificial corks can let air into the bottle after only 18 months storage, and they can also be difficult to pull out of the bottle and reseal afterwards.
A glass stopper should also prevents oxidation and cork taint, a popular brand is the VinoSeal. The disadvantages with a glass stopper for drinkers is the lack of that all important pop, while their relatively high cost means they are less popular with producers too.
The crown cap is the sort used on beer and cola. Despite the regal name you won’t find many quality wines using the crown, although it does provide a tight seal with no risk of cork-taint. These caps are used however during the process of making champagne and other sparkling wines.