Common Wine Faults and flaws and How to Identify Them

By Sara Cranmer

We all enjoy tasting delicious wines, but what if they don’t taste quite right? It’s helpful to be able to spot wine faults and understand why they occur as this can help enhance the customer’s experience overall.

By definition, wine faults are unpleasant characteristics of wine and may include elements of smell, taste or appearance. Most faults have a chemical or microbial origin and can be naturally present in wine at undetectable levels. When the concentration of these compounds becomes too much, they can overwhelm the desired aromas and flavours of the wine, rendering it undrinkable or faulty. And while no wine fault is harmful to human health, but some people are more sensitive to these undesirable characteristics. But wine is complicated, and there are more things that can go wrong than those listed here, but these are the main offenders.


Oxidised wine is potentially the most common wine fault. It occurs when wine is exposed to too much oxygen, either due to a faulty closure or if a wine has been open too long. As a result, the wine starts to turn brown, the aromatics fade, and a nutty, bruised apple character evolves. It’s exactly the same thing that happens when sliced apple turns brown.

Some wines such as sherry are deliberately made in an oxidative style and will display these characteristics. However, when found in young wines that are meant to be fresh and fruity, such as Pinot Grigio and Sauvignon Blanc, it is seen as a fault. White wines are much more susceptible to oxidisation than reds because the tannins in a red wine act as a buffer. Most oxidation is easily prevented by proper wine storage, using either with vacuum pumps or inert gas. 

Cork Taint

Did you know that about 2% of all wine bottled under real cork is affected by cork taint? Commonly referred to as corked wine, this doesn’t mean pieces of cork floating in your wine, but instead it refers to a chemical compound called TCA that contaminates the wine. Whilst this compound can usually be found in natural corks, it can also be present in the winery.

Cork tainted wines have a musty smell reminiscent of wet newspaper, mouldy cardboard, or wet dog, and any fruit flavours will be muted. The pungency of these aromas and flavours can vary from barely noticeable to overpowering. Cork taint cannot be removed from wine, so careful selection of quality bottle closures is important.

Heat Damage

Wines can be heat damaged during transportation or storage. This typically happens when wine is left in hot environments for prolonged periods of time, like wine cases cooking in the sun or bottles in direct sunlight in a shop window.

When this happens, the wine loses its fresh fruit characteristics and tastes dull and stale. It might have jammy, cooked fruit, nutty roasted sugar-type aromas. Heat damage often compromises the seal of the bottle (the expansion from the heated air pushes the cork out) and oxidisation can occur as well. To avoid this, wine should be stored a consistent, cool temperature around 12 degrees and out of direct sunlight. 

UV Light Damage

UV light damage or light strike damage occurs in wines that have had excessive exposure to ultraviolet light, most commonly from storing bottles under direct sunlight or near fluorescent tube lighting. The UV light reacts with components in the wine and creates sulfur-smelling compounds like rotten cabbage, or egg. Delicate wines such as Champagne or whites like Pinot Grigio are more at risk than reds, as these contain phenolic compounds that help protect it.

The French have even had the term "goût de lumière", which translates to a ‘taste of light’. To mitigate light, strike some producers will use dark coloured glass to protect the wine, and wine should always be stored out of direct sunlight.

Faults vs Flaws

In wine tasting, there is a big distinction made between what is considered a fault and a flaw. Wine flaws are minor attributes that are not normal wine characteristics, but the wine is still considered drinkable by most people and can actually add complexity and enhance the wine. However, when a flaw becomes so pervasive that it is all you taste, that flaw is now considered a fault. Here are a few examples of common wine flaws.   


Brettanomyces, sometimes referred to as ‘brett’, is a type of wild yeast found in wineries and has the potential to cause significant wine spoilage. It is most commonly associated with barrel-aged red wines, although it can also occur in white wines. Brettanomyces can be introduced to a winery by being naturally present on grapes or from Brett-contaminated barrels that then spread throughout the winery.

Brett dulls the fruitiness of wine, gives a metallic aftertaste and has a range of aromas like antiseptic, farmyard, horse, bacon and cloves, which vary in intensity. The sensory threshold for Brett differs between individuals and at low levels some people love these flavours, whilst others hate it. However, when the concentration is too high it is perceived as a definite fault.  Once a wine is affected by Brett, it cannot be removed so diligent winery hygiene is of upmost importance.

Reduction or Volatile Sulphur Compounds

Reduction is the term used to describe the presence of volatile sulfur compounds in wine and is a complicated issue. It can occur during fermentation when the yeast doesn’t have enough nutrients or oxygen. Usually, it can be rectified by the winemaker at this stage by aeration or adding nutrients, however reduction can sometimes re-appear when a wine is bottled.

There are variable characteristics of reduction. At higher levels, the aromas are very pungent and unpleasant and can range from rotten eggs, sewage, cooked cabbage, burnt rubber, garlic, and cat urine. Whilst at low levels the aromas may be described as smoky or gunflint and be reminiscent of struck matches which many people enjoy. It is thought that some volatile sulfur compounds are important components of the varietal character of Sauvignon Blanc. Reduction is most commonly detected when a bottle of wine has just been opened, but with exposure to air, the unpleasant aromas start to dissipate after a few minutes. However, if it doesn’t disappear then there’s perhaps a more complex disulphide problem which will spoil the wine.

(NB; Sulfur dioxide (SO2) is not to be confused with these volatile sulfur compounds and is not part of the reduction syndrome).

Volatile Acidity

Volatile acidity (VA) or vinegar taint, is a common wine fault and involves the formation of acetic acid and other related compounds by bacteria during the fermentation or storage of wine. Acetic acid can contaminate wine from damaged fruit, fruit flies and poor winery sanitation and will then proliferate with exposure to oxygen.

VA is undetectable at low levels and is used as a tool by some winemakers to develop complexity in their flavour profiles and ‘lift’ a wine, although there are different opinions as to what level of VA is appropriate for premium wine. At high concentrations it can make wine smell like vinegar and is sure to deem the wine faulty. Acetic acid and alcohol can then further metabolise into a serious wine fault called ethyl acetate which smells like nail polish remover.

What to do if a wine is faulty

If a wine doesn’t taste as it should then an alternative should be offered to your guest. At the end of the day, no wine faults are actually bad for your health and whilst cork taint, oxidation, light strike and heat damage are definite faults, others may be enjoyable! It's all down to personal preference.