Wine Faults Explained

Unfortunately, molecules which impart unpleasant olfactory and gustatory characteristics can occasionally be found in a bottle of wine. They are most often the result of poor winemaking practices and bad storage conditions, and the negative characteristics they bring about are known as wine flaws.

Some molecules only become unpleasant above a given threshold. In fact, for certain palates, they can have a positive impact on a wine at low concentrations. Up to certain concentrations, the majority of these molecules will simply mute the wine’s natural aromas and flavours or alter them slightly. At higher concentrations, however, they can render the wine undrinkable, and are then classified as wine faults.

The precise level of concentration at which these transitions occur depends entirely upon an individual’s sensory apparatus and experience. Wine tasting is a subjective exercise, which can be influenced by everything from the drinking environment to the shape of the glass being used. However, certain tastes and aromas, at high enough concentrations, will be considered unpleasant by most people, in any situation.

There are many causes for the development of wine faults. Many of these have their source in the winery. These include poor hygiene, excessive or insufficient exposure of the wine to oxygen, excessive or insufficient exposure of the wine to sulphur, overextended maceration of the wine either pre- or post-fermentation, faulty fining, clarification or stabilisation of the wine, the use of dirty oak barrels, over-extended barrel ageing, poor bottling practices, the use of dirty bottles, and the use of poor quality corks. Outside the winery, causes amount to poor storage and transport conditions in which the wine may be exposed to excessive heat, light, or temperature and humidity fluctuations, be the transport in bottle or in bulk, and be the storage in a warehouse, shop, or private cellar. There are many opportunities for wine faults to develop, and they can occur as a result of carelessness or oversight on the part of the winemaker, the wholesaler, the retailer or even the end user.

The following is a list of the most common wine faults found in wine and the main molecular compounds that give rise to or are associated with them:

Cork Taint



Oxidative Taint

Acetic Acid (Volatile Acidity)


Ethyl Acetate

Sulphur Taint (“Reduction”, Light Strike)

Hydrogen Sulphide

Ethane Thiol

Methane Thiol

Diethyl Disulphide

Dimethyl Disulphide

Dimethyl Sulphide

Ethyl Thioacetate

Methyl Thioacetate

Microbial Taint


• 4-Ethylguaiacol

• 4-Ethylphenol

Lactic Acid Bacteria

• Diacetyl

• Geraniol


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