Santa Margherita

Sometimes it may happen that you notice disagreeable odors, which are caused by faults in the wine. There are certain factors that, even they are not the actual cause, favor the onset of problems, because they are symptoms of weakness or instability in the wine. Examples are:

•    a low level of alcohol (<11.5%-12%)
•    low acidity (pH >3.4 in whites and >3.6 in reds)
•    the presence of residual sugars
•    a low levelof tannins (in red wines)
•    incorrect or insufficient use of sulphur dioxide
•    a high level of assimilable nitrogen
•    storage at high temperatures.

The best known odor is that of cork taint, which we perceive on the nose but even more clearly on the palate. This is passed on to the wine from the cork when it is attacked by parasitic fungi (the trichloroanisole or TCA molecule).
Another fault may be a smell of refermentation and dregs (a disagreeable odor rather like drains or flatulence) which comes from the wine having been in contact too long with dirty, oxidized lees or from wines that have undergone an unwanted (and therefore uncontrolled) second fermentation in the bottle. This often happens with wines purchased in demijohns and bottled at home.
A third fault may be caused by bacteria that develop in barrels that have been badly looked after and which have not been cleaned with the proper antiseptics (a smell of dry or rotten wood). Yet another comes from grapes that are not perfectly healthy,  giving off odors that are reminiscent of pharmaceuticals or of a dry-cleaner's. The smell of oxidation (like that of Marsala or Madeira) is due to excessive contact with oxygen. This is an irreversible process and is a serious fault, except for those wines (such as Marsala, for example) whose main characteristic is that they are oxidized.
Another fault one often comes across is reduction (a closed-up, slightly musty odor), which is perceptible in wines that have spent a long time in bottle or at any rate in an environment where oxygen is lacking. Sometimes it disappears or weakens if the wine is allowed to “breathe”.
A smell of sulphur is caused by excessive use of sulphur dioxide. This is noticeable both on the nose and on the palate and is similar to the smell of wax matches or wet wool.
One may also find the smell of rotten eggs (hydrogen sulphide), an irremediable fault caused by adding too much potassium metabisulphite prior to the fermentation; it can also result from a process of reduction during the alcoholic fermentation.
The smell of vinegar, or acescence, is due to the presence – beyond acceptable limits – of acetic acid (volatile acidity). It is particularly perceptible on the nose because of the correlated formation of ethyl acetate because of the activity of acetic bacteria (an aerobic environment, blocked fermentation, etc.)
A fault that one finds increasingly often in wines, and particularly in reds, is the smell of animal sweat or of stables; this is connected to the presence of ethyl phenol from the fermentation of Brettanomyces yeasts (in jargon the fault is referred to as Brett). Wines made from certain varieties (such as Cabernet or Lagrein) are prone to Brett, but especially the contamination of wooden containers (such as barriques) can cause the onset and spread of this fault in wines that are matured in them.
Also, too marked a note of bell peppers, which is characteristic of Bordeaux varieties like Cabernet Sauvignon, Cabernet Franc and Merlot, or a dominant smell of cat’s urine that one finds in some Sauvignons should not be considered – as many people maintain – typical of their respective varieties, but rather as real faults caused, in the vast majority of cases, by the grapes’ failure to reach full aromatic ripeness.