Wine Faults, from www.wineanorak.com

Acetic Acid
A volatile organic acid often encountered in food, this is the main acid responsible for the flavor of vinegar. From this you'll have gathered that it is not a desirable component of wine. If you leave a bottle of wine open for a couple of weeks, a bug called Acetobacter will turn the alcohol into acetic acid, and you'll have vinegar.

Astringent
Unflattering tasting term describing an unpleasant, dry, mouth-puckering sensation usually caused by excess acidity or bitterness. The excessive tannins in young, overextracted red wines are the usual culprits.

Austere
Wine-buff speak for a wine that is a bit too severe or restrained on the palate. Usually uncomplimentary, although some young wines destined for greater things may be 'austere' in their youth. Commonly used to describe young Bordeaux reds.

Brettanomyces
Have you ever had a wine that tasted of a mixture of farmyards, cheesy feet and animal poop? The chances are, this wine was infected by the yeast-like fungus Brettanomyces (often abbreviated to just 'brett'). It is often encountered in red wines from warm regions such as the South of France. In small doses can add complexity, but in higher concentrations is thought to be a fault. Once present in a winery Brettanomyces is quite difficult to remove.

Clean 
A wine which doesn't have any off-flavors or taints is called 'clean'. Most wines on the market these days are 'clean.'

Corked 
Have you ever opened a bottle, and instead of clean, fruity aromas found that it smells of moldy cellars and damp cardboard? This is what a corked wine smells like. Contrary to popular opinion a corked wine is not one that has bits of cork floating in it (this is totally harmless, fish the bits out and the wine will be fine); instead, it is a wine that has been contaminated by a chemical called trichloroanisole (TCA). The human nose is extremely sensitive to this contaminant (it can be detected at concentrations as low as parts per trillion!), which is a result of a chemical reaction between chlorine and cork. It is a major problem, spoiling between 2% and 7% of all wines, depending on who you listen to. This is why artificial corks are increasingly being used, especially on inexpensive wines not destined for ageing. The degree of cork-taint can vary, but you'll find that almost all retailers will replace a corked bottle without question if you return it.

Flabby 
A word used to describe a wine that doesn't have enough acidity to balance the other elements. Buttery Chardonnays with rich tropical fruit flavors from warm-climate regions are most likely to show this sort of character, especially if they are a few years old.

Gamey 
Imprecise taste term usually reserved for older wines that exhibit smells and flavors associated with damp undergrowth, mushrooms, well hung pheasants and unwashed farmers' feet.

Hard 
A negative tasting term for a wine has a tough tannic structure, perhaps also with high acidity or bitterness, and very little *fruit to provide balance. Such wines are joyless bottles, unpleasant to drink. Hardness can be contributed by unripe grapes, too long a maceration, or overextraction. However, all is not necessarily lost, because some wines destined for long ageing often start out tasting 'hard' in their youth, and then mellow with time. A good example of a hard wine might be a young Barolo, from Piedmont in Italy.

Lean 
Tasting term referring to a wine that has high acidity and not much fruit.

Musty 
Think of damp cellars, think of moldy potatoes at the bottom of the bag, think of railway arches -- these smells can be described as musty, and when you encounter mustiness in a wine, it could well be because it is *corked.

Oxidized 
A term describing a commonly encountered wine fault, caused by the exposure of a wine to oxygen, which eventually turns the alcohol to *acetic acid. Net result is vinegar. Yuk. A mildly oxidized red wine will have a brownish color, with high *volatile acidity. A mildly oxidized white wine will have a deep yellow/gold color and unappealing flavors of butterscotch and coffee, perhaps also with some volatility on the nose. The most common cause of oxidation is cork failure, letting air into the wine, although white wines intended for early consumption that have been cellared for too long will also display these characters to varying degrees.

Reduction
'Reduction' is the term used to describe the presence of volatile sulfur compounds in wine. It’s actually a bit of a misnomer. Let me try to explain why. Reduction and oxidation are two different chemical processes that complement each other. In a chemical reaction, electrons change hands, and as one compound is oxidized another is reduced. If there is plenty of oxygen around, then chemical components in a wine will be gradually oxidized (the electrons are transferred from the chemical components in the wine to the oxygen). The end result is an oxidized wine. During fermentation the yeasts need oxygen, and in the early stages of red wine development a little oxygen is helpful because it allows the oxidation of some ethanol to acetaldeyde (also known as ethanal) which can then help with the development of tannins and pigmented polymers that are important in building structure and colour (this is the theory behind microoxygenation). But after this, wine development is largely reductive: that is, it occurs best in the relative absence of oxygen.

TCA 
An abbreviation for the chemical trichloranisole, which ruins an enormous amount of wine every year (see *corked).

Volatile Acidity
Volatile acidity (VA) is caused by naturally occurring chemicals in wine, produced by the actions of acetic bacteria.  It can be shown that there are measurable levels of VA in all wine. VA is split between two types of chemical – acetic acid and ethyl acetate.  Rightly or wrongly, I tend to think of the acetic acid affecting the taste with the sourness or edge to a wine which recalls vinegar, with the ethyl acetate leading to various volatile traits from a mild ‘lift’ to the nose which isn’t directly noticeable, through a boot polish kind of aroma, to nail varnish remover in the worst cases.  The fact is that acetic acid and ethyl acetate are formed together and such a distinction may not in fact be so straightforward.  But then that’s wine for you – it is more than likely that a complex picture of elements are involved in whether we perceive an issue or not.  In the case of VA, it’s not just the level – but also the wine style and type.  The richer, bigger wines (Port, for example) can carry greater amounts of VA without detriment.  In fact, the sweet dessert wines styles affected by noble rot actually seem to need high levels of VA in order to help form the nose.  Without these more volatile elements, the heavy, sugary wine would not give much on the nose at all, and the VA provides an essential ‘lift’ to bring the less volatile elements to our nose.