Collective term for defects or undesirable and unacceptable faults in the wine, which are expressed mainly by unpleasant to disgusting smell and/or taste or "only" in appearance (haze, turbidity, crystals, etc.). They are determined, among other things, during a wine evaluation and wine appeal, whereby such wines then fall out of the evaluation in the case of certain faults or to a certain extent. Sometimes a distinction is made between wine faults (wine defects) and wine diseases. The latter are changes in wine caused by micro-organisms(bacteria, fungi, viruses), which can increase in intensity if appropriate countermeasures are not taken.
Whether a certain smell and taste is already perceived as a fault is subjective in some cases. For there are some borderline cases where a certain smell or taste is pleasant and positive for one person, but unpleasant or even faulty for another. Examples of this are the typical petroleum tone of a Riesling or the earthy smell and tone of a red wine known as horse sweat. In addition, however, there are objectively identifiable general defects that deviate from a specific standard. They range from barely or weakly perceptible to unpleasant and spoiled and also depend on experience and sensitivity. A good example is the notorious cork taster, which can be recognized by trained persons even at the slightest degree. With appropriate experience, wine faults can be detected or identified quite accurately. This can also be learned, various manufacturers offer aroma sets for this:
In most cases, however, sensory evaluation is not sufficient for accurate identification. The causes of wine defects can occur already during the growth of the grapes and then during the entire processing chain from harvesting to bottling, but also afterwards during bottle ripening. In most cases, they are chemical and microbiological processes triggered by microorganisms such as fungi or bacteria or complex reactions of various substances. Causes can also be of a physical nature, such as too much contact with oxygen.
The smell and taste of a wine is composed of many chemical compounds. The total extract of a quality wine is between 17 and 30 g/l. Of this, the aromatic substances account for 0.8 to 1.2 g/l. For almost all wine faults, the substances causing them are now known. These mostly extremely small quantities are indicated in milligrams (mg = thousandth), micrograms (µg = millionth) to nanograms (ng = billionth) per litre. For the latter, this means a single grain of ten tons of wheat. They are perceived from a certain amount, which is called the perception threshold: