Collective term for defects or undesirable and unacceptable faults in wine, which manifest themselves primarily through unpleasant to disgusting odour and/or taste or "only" in appearance (haze, cloudiness, crystals, etc.). They are detected, among other things, during a wine evaluation and wine address, whereby then with certain faults or a certain extent such wines are dropped from the rating. 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 defect is subjective in individual cases. 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 petrol tone of a Riesling or the earthy smell and tone described as horse sweat of a red wine. Beyond that, however, there are objectively ascertainable generally valid defects that deviate from a certain norm. They range from barely or faintly perceptible to unpleasant and spoiled and also depend on experience and sensitivity. A good example is the notorious cork taint, which is recognised by trained persons even at the slightest level. With the appropriate experience, one can recognise or identify wine faults quite accurately. This can also be learned; various manufacturers offer aroma sets for this purpose:
Mostly, however, sensory evaluation is not sufficient for accurate identification. The causes of wine defects can already occur during the growth of the grapes and then during the entire processing chain from the grape harvest to bottling, but also afterwards during bottle ageing. In most cases, these are chemical and microbiological processes triggered by microorganisms such as fungi or bacteria or complex reactions of different substances. Causes can also be of a physical nature, such as too much contact with oxygen.
The smell and taste of a wine is made up of many chemical compounds. The total extract in a quality wine is between 17 and 30 g/l. Of this, the aroma substances make up 0.8 to 1.2 g/l. For almost all wine faults, the causative substances are now known. These mostly extremely small amounts are given in milligrams (mg = thousandths), micrograms (µg = millionths) to nanograms (ng = billionths) per litre. In the latter case, this means a single grain of wheat out of ten tonnes of wheat. They are perceived above a certain amount, which is called the perception threshold: