Spotting a faulty wine

It is important to know when a wine is faulty, as opposed to just not to your taste, so that you can return it - either to the supplier or in a restaurant. There are several important faults that are easy to spot, but wines can also be atypical rather than faulty. Faults tend not to be absolute, but rather along a continuum. At some thresholds a fault can actually enhance a wine whereas a little more will make it undrinkable (brettanomyces or volatile acidity). Different people have different detection thresholds of potential faults in wine, but also there are some problems that are just plain wrong.

Visible faults

A wine should always bear clean, clear and bright, occasionally opaque but never cloudy. Wines can be hazy or cloudy, and this is usually because it is in some way, unstable. It is usually due to growth of yeasts or bacteria, but may, more benignly be due to unfiltered proteins in the wine. These wines should all be sent back.

Occasionally clear crystalline precipitates can be seen on the bottom of the cork, or in the bottom of a bottle of white wine. These are totally harmless and are the result of excess potassium or calcium tartrates, but they can look a bit like shards of glass. Simply leave these in the bottle as you pour; there is no need to send such wines back.

Wines can occasionally have a slight spritzy bubble to them. In white wines this is often simply because they have been bottled with a little carbon dioxide to make them refreshing, in which case it is not a fault. If there is a slight fizz in an older wine or a red wine this is more of a problem and is usually due to some re-fermentation of the wine in the bottle. It may well be accompanied by off-aromas, or a grapey smell and cloudiness. This is not good.

Cork taint – or the ‘corked’ wine

The most famous and most mis-understood of all wine faults. It is being fast eliminated by the introduction of plastic corks and screw-caps. However it is estimated that between 5-10% of all wines sealed under cork have some degree of taint. It has nothing to do with bits of cork floating in your glass – these simply need fishing out before drinking up. True cork taint makes the wine smell flat and dusty, rather like damp cardboard. Where the taint is slight it may appear simply to lack fruit and be uninteresting, but if left in the glass it will gain aromas of mould and mushrooms. The flavours are much the same and when the problem is really bad it is completely undrinkable. The causes of cork taint are a cork infected with a fungus that produces a chemical called 2,4,6 –trichloroanisole, or TCA. It is this chemical that imparts the off-flavours to the wine and can be detectable at a threshold of only a few parts per trillion.

Oxidation

Oxygen is vital to the development of wine. The interaction between the wine and the small amount of air below the cork, over many years, may be one of the mechanisms by which wine develops when 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, rampant oxidation will rapidly ruin the wine. Oxygen is an aggressive element, and will interact with most substances, resulting in their degradation. It's what makes steel turn to rust, turns butter rancid and freshly cut apples brown. Fruitless, flat wines with a flavour profile resembling old and tired Sherry may well be oxidised. White wines may also become deeper and more golden I colour as they become oxidised. Sherry and Madeira are deliberately oxidised as part of their production process to give them that distinctive ‘rancio’ character.

Sulphur dioxide

This is vital to the winemaker as an all purpose disinfectant and antioxidant for stabilising wines. However when used with abandon, it can be detrimental to a wine and it will produce a burning sensation in the throat and make you cough and sneeze when you smell the wine.

Reduction

Sometimes a wine shows aromas of burnt rubber, garlic, burnt matches and mothballs, and this is due to the formation of hydrogen sulphide in a wine (which in turn originates in a lack of nitrogen in the grapes during fermentation). This hydrogen sulphide in a wine can be removed by swirling the wine around in the glass and aerating it, or by dropping a copper coin in the wine for a few moments - if you want to know the chemistry of this, email us! If the off aromas persist it means that the hydrogen sulphide has bound to the colour components in the wine to form mercaptans and this is a permanent fault in the wine and you should send it back. Reduction is a problem more commonly found in wines under screw cap than cork, because the cork will often absorb the off-aromas, ensuring the wine is clean by the time it is poured.

Volatile Acidity (VA)

All wines have some volatile acids, the most common of which is acetic acid. At low levels this can improve a wine’s complexity but when it is at fault-levels, it can smell positively vinegary. At this point it is probably slowly turning into vinegar due to bacterial spoilage.

Mustiness

Sometimes a wine can smell just a little musty or dusty, but not as bad as cork taint. This can be due to insufficient cleaning of pipes, tanks or barrels. This is more likely in traditional style wines rather than modern style wines that have been fermented in stainless steel.

Cooked wine

This is one of the most common wine faults because it relates to poor storage conditions, in particular, the exposure of the wine to high temperatures. When a wine is exposed to high temperatures, the liquid expands and this 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. Never buy a bottle where the top of the cork doesn't sit flush with, or below the level of, the mouth of the bottle. If you inspect the level of wine in the neck of the bottle, it shouldn't be too low. There's always some slight variation between bottles, but for everyday wines the level should be well into the neck.

Cooked wines taste just like that - as if they've been cooked. There won't be any freshness to the fruit aromas or flavours - instead you'll get a stewed, prune-like profile on the palate, the wine often seems thin, lacking body and character. As with all wine faults, there is a spectrum of severity, and some wines may be borderline, leaving you wondering "Is this a bit cooked?". But if you get a full-blown one, you'll know it.

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