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Tasting Wine

Wine faults

  • The information provided by the visual examination is much less important than the aroma. The nose of the wine is analyzed for condition (cleanliness), intensity, development, fruit character and wood treatment.


    The first impression will be one of cleanliness. Off aromas, including corkiness, oxidation, volatile acidity, reduction (hydrogen sulfide and mercaptans), mousiness and sulfur aromas all indicate problems in grape growing, wine handling, storage or stabilization.

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  • TCA taint is the pungent aroma of wet cardboard that indicates a “corky” wine. This is produced by the metabolism of bleach used in cleaning the corks by penicillin bacteria infecting the cork. It can also be present in treated wood used in the winery. TCA can be sensed at very low levels, and tasters vary in their ability to perceive it. It can be sensed at levels as low as 2–3 parts per billion, and is one of the most pervasive wine faults.

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  • Exposure of wine to oxygen is another common problem often detected on the nose. Low levels of oxidation are noted as a lack of fruit and a vapid or flat character. This is caused by a reaction between the oxygen and the alcohol, which produces acetaldehyde. This compound is the distinguishing character of some fortified wines, such as Sherry and Madeira and its presence in table wine is referred to as “maderization.” Higher levels can cause a wine to develop unpleasant meaty or caramel notes.

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  • Volatile acidity is another fault evident on the nose. It is produced when acetic bacteria (acetobacter) infects the wine in the presence of oxygen. The alcohol is oxidized into acetic acid, which reacts itself with the alcohol, producing ethyl acetate, an ester. Ethyl acetate in very small quantities can enhance the fruit character of the wine, but in higher concentrations can give an unpleasant “nail polish” aroma.

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  • In an understandable effort to avoid oxidation and the development of volatile acidity, many winemakers limit the exposure of wine to oxygen. If their efforts are too successful, however, it can lead to the development of reductive odors (such as hydrogen sulfide and mercaptans). Reduction is the opposite of oxidation. Some oxygen is needed in during wine production, and if it is not available, then hydrogen molecules can combine with the sulfur in the wine to produce hydrogen sulfide.

    This is the compound that can give a wine a “rotten egg” smell. This aroma can be dispelled by aeration, but if it is not eliminated, it can combine with carbon molecules in the wine, leading to the development of mercaptans. These skunk-like aromas are nearly impossible to remove. Some tasters do not see low-level presence of mercaptans as a fault, however, and believe that they add to the complexity of the wine.

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  • An unpleasant animal aroma usually described as “mousy” is produced by the action of Brettanomyces (Brett for short), a common variety of wild yeast. This fault can be difficult to detect on the nose, and is usually more apparent on the palate. It is also an element that is thought to add complexity in small doses, although some tasters are very sensitive to it. In larger quantities, Brett destroys the aroma of the wine.

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  • Lactic souring is caused by the action of lactic bacteria consuming the lactic acid in the wine if it has not completed malolactic fermentation. This can give rise to sourdough or fermenting cabbage aromas that can be quite unpleasant.

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  • Sulfur dioxide is an agent commonly used in wine production. It helps prevent oxidation by combining with oxygen before the wine will, and it also kills bacteria and yeast, helping to prevent the formation of acetic acid, lactic souring and Brettanomyces infection. It is widely used by nearly all winemakers, and those who seek to preserve the fruit character above all will be more generous in its application. This can lead to its aroma being present on the nose of a wine as a telltale “burnt match” smell and a burning sensation on the palate. This, again, is a fault to which some tasters are more sensitive than others.

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