Wine Faults

From the time wine grapes are harvested until the moment the wine reaches your glass, wine is subjected to various environments and processes, all of which will have some influence on the quality and taste of the wine. Despite the development of screwcaps and synthetic corks, temperature-controlled storage and improvements in hygiene and sanitation in wineries, it is still occasionally possible for wine faults to occur. Faults may be detected at any stage of the tasting process. If you've ever opened a bottle of wine and found that it 'tasted funny' or 'didn't smell quite right', but weren't entirely sure why, read on.

Visible faults

As a rule, wine should be clear, and free from any haziness. A visible haze in wine may be an indication of poor stabilization or fining, which has led to yeasts or other residues remaining in the wine. This will be a very fine, persistent haze, and is not to be confused with sediment or precipitates, which slowly fall to the bottom of the bottle. Sediment is in fact sometimes seen as a positive thing, as it is a sign that a wine has received little or no filtration, preserving as much of the wine's character and as many flavour compounds as possible. It may also indicate a degree of bottle-age.

Although sediment is most commonly found in red wines, unfiltered white wines may also throw a sediment of harmless tartrate crystals (resembling tiny grains of glass or frost). These are most common in sweet wines, or other unfiltered whites, especially when they have been stored chilled for a period of time. Sediment can be removed by allowing the wine to settle and then decanting, or by gentle filtration through a wine strainer.

Bubbles are another fault which may be detected visually. Visible, persistent bubbles in what ought to be a still wine, may indicate that the wine has undergone a secondary fermentation after bottling, and will usually be accompanied by an unpleasant flavour. However, a few wines such as Vinho Verde are deliverately bottled with a very slight sparkle.

Smellable faults

Your nose is the most useful tool for detecting faults in wine, as most wine faults will result in some kind of perceptible aroma. The four most common faults to be detected on the nose are:

Cork taint: This is caused by a chemical (TCA) that can occur naturally in cork bark which leads to contamination of the wine. A wine which has become 'corked' will have an unmistakably musty smell, similar to mould or damp. The wine is unfortunately irretrievable, and the odour only gets worse with exposure to the air. One point to note is that traces of mould on the outside of a cork may be a result of damp cellaring conditions (good for maintaining an effective seal where traditional corks are concerned), and is not necessarily an indication that the wine inside is corked, so always rely on your nose!

Oxidation: This is when a wine has been allowed to react with oxygen, possibly due to unsuitable storage conditions or a faulty closure allowing air to enter the bottle. The wine will have a stewed prune or sherry-like aroma, and may also have developed a brownish appearance. A small degree of oxidation is to be expected for many older wines (such as aged red Bordeaux or Rioja), but is undesirable in young wines, in which fresh fruit flavours and vibrant colour are important.

Acetic acid: In simple terms, the smell of vinegar. A small amount of acetic acid is nearly always present in wine, as it is a natural by-product of the fermentation process. A vinegary smell or taste is common in wine which has been left open for a few days, especially if stored un-refrigerated. However, any acetic characteristics should be virtually imperceptible from a newly opened bottle. A strong smell or taste of vinegar may suggest the presence of bacteria or active yeasts in the wine.

Sulphur: Sulphur dioxide has been used in winemaking for centuries for sterilising barrels and for killing yeasts, hence helping maintain the freshness of a wine once bottled. Provided its use is carefully managed in the winery, only a slight sulphurous odour, redolent of eggs or struck matches, will ever be noticeable in a wine, but occasionally it may be unpleasantly strong. The smell is usually most prominent in white wines, especially those sealed with screwcaps or other synthetic closures which preserve aromatic compounds very effectively. Mild sulphurous odours can often be reduced with exposure to air or by aggressive swirling of the wine.

Tasteable faults

It is rare to experience wine faults which are only detectable on the palate, the vast majority of faults having already come to light with a good sniff of the bouquet. The wine's flavour or texture will usually only serve to confirm what is suggested by the smell.