Even though wine making technology allows the production of quality wines, sometimes it can be possible to find some faults that can compromise in a relevant way both the evaluation and quality. Talking about faults in wines, even serious ones, can be seen nowadays as a rather unusual subject as it seems to happen less and less frequently, however a wine taster should be able to recognize the many faults, at least the most common ones, and subsequently determining the quality of wine. Quality of wine, as it is clearly and obviously known, is also defined by means of the absence of faults and, in particular, with the presence of all those factors that promote quality.

 Finding a wine which has faults in its aspect is nowadays rather rare. Thanks to the modern and proper wine making practices, wines produced are limpid and crystalline, with a total absence of “substances” or conditions that would compromise its aspect. It can be said that certain faults and certain wine diseases that could seriously compromise wine's aspect and its aesthetical pleasantness have practically disappeared, their presence in wine, besides being a rather exceptional fact, are also the sign of an approximate and coarse wine making.

 A wine, that can be considered of quality at least in its aspect, must always be limpid and the presence of suspended particles is always and however a negative factor that compromise its quality. However it must be remembered that sometimes the presence of suspended particles in the bottle, never in the wine glass, is to be considered as normal and do not compromise wine's quality in anyway. Sometimes can happen that a layer of sediment can develop in the bottom of the bottle and this usually is to be considered as a natural consequence or reaction related to specific events.

 In red wines, particularly the ones which are destined to a long aging and rich in tannins and extracts, it is absolutely normal that in the bottom of the bottle can be found some sediment and they are formed by polymerized tannins and, by getting more and more heavier and less soluble, they finally deposit to the bottom. This cannot be considered as a fault because, besides being absolutely a natural consequence of the aging of such wines, a proper decanting will give a perfectly limpid wine.

 Another factor that can be cause of sediment is related to the precipitation of the so called “tartrates”, which can be mainly found in white and rose wines, and is caused by a thermal shock as a consequence of a sudden and prolonged cooling of wine. The deposit of tartrates can be recognized by the presence of transparent crystals on the bottom of the bottle, pretty heavy, and they will hardly be in suspension in wine. No matter this is a “forgivable” fault, the precipitation of tartrates is however a factor that compromise the aesthetical pleasantness of wine and therefore must be avoided.

 Causes that really compromise the aspect of wine, particularly wine's limpidity, are all related as a consequence of a scarce stabilization of wine or because of refermentations occurred in the bottle. This phenomenon is rather rare to find, however there are cases where it can be still found. This condition is mainly originated by two distinct causes: alcoholic refermentation and malolactic refermentation, both occurred in the bottle. Alcoholic refermentation in bottle takes place when the wine is bottled when it is not perfectly stabilized and it still contains some non fermented sugar. Malolactic refermentation is instead caused by the presence of microorganisms which transform malic acid into lactic acid. Both phenomena can make wine turbid because, in case of alcoholic refermentation, saccharomyces transform sugar into alcohol, and as a byproduct, carbon dioxide, whereas in case of malolactic refermentation, lactic bacteria transform malic acid into lactic acid and, as a byproduct, carbon dioxide. In both cases, at the end of the refermentation, microorganisms die and deposit to the bottom of the bottle and they can be recognized as a grainy and sandy layer making wine turbid. In both cases the wine, besides being cloudy or turbid, according to the origin of the phenomenon, also has some slight effervescence.

 There also are other causes which compromise wine's appearance, such as the so called “casse” (breaking) and other diseases which are now very rare and therefore very, if not impossible, hard to find. Another fault that can be detected in wine's appearance is the wrong correspondence of its color, showing brownish colors both for white wines and red wines, which is the sign of a strong oxidation or a condition of wine's life that passed its best state and it is not pleasing to drink anymore, in other words, a wine which is very old and died. The cause for this fault is to be found in the bad keeping of bottles or because wine was aged for too long in bottle. In this specific case it is more likely that wine, besides not being pleasing at sight, is also disgusting both at mouth and nose. Moreover it should be noticed that oxidation, when it is found in young wines, is a grave fault that can be originated by producer's negligence in keeping.

 As opposed to wine's appearance faults, olfactory faults are more frequent and, in case they are present, they seriously compromise wine's quality. Among the main and most feared ones which affect wine's aromas, there is the so called “corky smell”, a fault that affects about 5-7% of the total quantity of wine sold and is exclusively found in bottles sealed with corks. This fault develops because of 2,4,6--tricloroanisole, or simply tricloroanisole, abbreviated as 246--TCA or TCA, which can be found in some corks as a consequence of causes hardly foreseeable. Describing corky smell is rather hard, however once this smell is detected for the first time it is rather hard to forget. The smell of this fault can be described as a set of odors that can resemble mold, wet cardboard or newspaper and putrefying organic substances.

 Corky smell is certainly the most common and recognizable olfactory fault, however there also are other faults, to be honest not very common because of the modern wine making techniques, and it is however important being able to recognize them when present in wine. The origin of these faults is related to organic chemistry and therefore the explanation of such chemical phenomena responsible for these smell is not covered by this article. It must be however noticed that some bad smells, and therefore olfactory faults, when are present in small quantities can be considered as pleasing to some individuals and, in this specific case, it seems to be true the renowned Latin saying “De Gustibus Non Est Disputandum”, there is no dispute about tastes. Moreover it should be remembered that perception of any smell, and therefore of any fault, is subjective and also depends by the minimum threshold of perception of every individual.

 The following list mentions the most common olfactory faults, as well as the cause which originate them and the characteristics that allow their recognition.

• Banana - No matter this aroma is considered as pleasing in certain white wines, it can be considered as a fault when it is excessively present and, even worse, when it is detected in red wines. The cause of this defect, also remembering that the aroma of banana is a typical characteristic of many grape varieties, such as Chardonnay, is usually a byproduct of malolactic fermentation.
• Band-Aid, Manure, Horse blanket - It is a sign of the presence of brettanomyces, a family of yeasts which usually have the effect of spoiling wine. It must be noticed this smell, in tolerable quantity, can be a wanted characteristic by the producer, in particular in Californian Syrah or in some red wines from Burgundy.
• Burning match, Sulfur - It is the sign of an excessive presence of sulfur dioxide. It should be however noticed that this component is always present in wine, both because it is a byproduct of fermentation and because it is used in the wine making in order to stabilize wine. When present in little quantity its smell is imperceptible and does not disturb other aromas.
• Canned asparagus - This fault can be mainly found in wines made of Sauvignon Blanc and it usually is the sign of a bad or approximate cultivation of vine or a grape not perfectly mature.
• Sweat, Dirty socks - This fault is usually the sign of a spoilage from bacteria of dirty casks
• Butter - This aroma is usually considered as a fault when present in excessive quantities, however it is a pleasing characteristic of certain white wines. The cause of this fault is to be found in the excessive presence of diacetyl that is usually developed during the alcoholic fermentation as well as during malolactic fermentation.
• Mold - It is always the sign of a bacterial spoilage, mouldy grapes or dirty casks.
• Enamel, Acetone - It is the sign of the presence of ethyl acetate, whose smell is rather pungent, and is the result of the combination between acetic acid, usually present in wine, and ethanol, that is the main wine's alcohol.
• Rotten eggs - It is the sign of the presence of hydrogen sulfide, a gas that can develop at the end of the fermentation and resembles the smell of rotten eggs. The development of this gas can also be cause of sulfur applied late to grapes, or in case the grape juice is poor in nitrogen, such as the one of Chardonnay, Riesling and Syrah.
• Alcohol - Alcohol is naturally present in wine, however when its smell is clearly perceivable and in a predominant way, it is considered as a fault.
• Sauerkraut, Boiled cabbage - It is usually developed as a byproduct of malolactic fermentation.
• Marsala, Sherry - The typical and loved aroma of these wines can be sometimes perceived in other wines and when this happens it is always sign of an excessive and sudden oxidation that affects, moreover, the aspect of wine as well.
• Garlic - It is the sign of the presence of mercaptans and sulfur compounds. This odor is usually the result of the combination of many sulfur components and they usually develop after the fermentation.
• Vinegar - It is the result of an excessive presence of acetic acid and it is caused by acetic bacteria present in wine in case alcoholic fermentation was not done in a proper way or in case alcohol, oxygen and acetic bacteria combine one to each other.
• Wet cardboard, Dog fur - It can be clearly perceived in case the cork is faulty and originated the so called “corky smell”.

 Faults that can be found is wine's taste are usually anticipated by olfactory analysis: a wine having bad smells will certainly and probably have a bad taste as well. This gets more evident with all those bad smells, such as vinegary smell, that can be easily confirmed in mouth. It must be however noticed that a wine which is very tannic or has some bitter flavors will never be anticipated by the nose or by its aspect. It should be remembered that in case of tannins, this can be a wanted characteristic by the producer who especially created that wine with the explicit idea goal it should be aged for sometime before being uncorked. In this specific case it is not right to talk about faults, indeed that bottle of wine was opened in advance and therefore the wine is “unripe”. A prolonged aging of the wine in the bottle will certainly make the same wine less aggressive and more balanced. The huge presence of tannins, or of any other gustatory element, such as acidity or alcohol, directly affects the determination of balance; a wine having a scarce balance can be considered as faulty, that is lacking of a fundamental quality factor.

 Even persistence, that is the quantity of time in which the gustatory-olfactory sensations of wine are perceivable after it has been swallowed, can be considered as a fault when it is not sufficiently long and it disappears within few seconds. It must be noticed this characteristic is to be considered as a lacking instead of a real and proper fault, what is certain is that when wine is short, that is lacks in persistence, it is disappointing and therefore this can be also considered as a fault even though of lesser gravity. In case a wine is short, it does not mean it was made with arguable or approximate wine making techniques, it is also true that persistence is created, as to say, both in the vineyard and in cellar, however it should be remembered that the quantity of time wine's taste lasts in the mouth and it is clearly perceivable after it was swallowed also depends by grapes varieties used to make the wine as well as the meteorological condition of the year, lastly, by the yields per hectare harvested in the vineyard.