Chances are that you have sipped a wine and thought that it did not taste quite right, but you were not able to pinpoint why. That's because the wine may have suffered from a fault affecting the aromatics or taste.
The modernisation of winemaking, improvements in hygiene, and tighter quality control measures mean that faulty wines occur less often. But a small percentage of wines may still have faults. This is not generally a food safety issue, but the wines don't make for a pleasant drinking experience. Some of the problems include:
Oxidation is probably one of the most common problems. It affects the colour of the wine. Young whites may have turned from a bright gold to dark lemon with tints of brown. A ruby, purple red wine will appear to have an orangey/ brown tint. The fresh fruit aromatics may be dull and the wine may be lacking in freshness on the palate.
You can try an oxidised wine by re-tasting a wine from a open bottle after a few days. The aromas will have lost the fresh and vibrant fruit character and it may taste stale.
Oxidation can happen at any stage of the process. It may be traced back to the winemaking stage when insufficient antioxidants were added. It may be due to improper temperature conditions during transport or storage. High temperatures will increase the rate of oxidation. Or it may happen during bottling, when too much oxygen comes into contact with the wine.
If at a tasting you hear the exclamation 'the wine is corked', the taster is alluding to it smelling musty or damp. It robs the wine of its fresh fruit aromas. Not everyone is sensitive to cork taint. The problem is due to a chemical compound found in cork called TCA (2,4,6-trichloroanisole). Producers have addressed this problem by switching to other forms of closures, such as plastic corks, screw caps and by using better quality cork.
Microbes play a positive role in wine. Without yeast there would be no fermentation and no wine. But microbes can adversely affect quality. For example, a yeast called Brettanomyces is responsible for adding savoury, meaty aromas to the wine. This makes the wine more interesting and complex. But in excessive amounts, the yeast creates extremely earthy tastes which flatten any fruity aromatics. So what one person may like is perceived as a fault by another. It all comes down to personal taste. But with better hygiene in the cellar, microbial spoilage in wines is less common.
Tartrate crystal issues
Most wines are supposed to be clear and bright. If you spot some crystals that look like tiny glass fragments in your wine, do no not panic. This may be due to tartrate crystals (potassium bitartrate), which have not been removed during the winemaking stage. They are harmless and will not have any impact on the taste of the wine.
Perhaps there is nothing wrong with the wine - the problem may be with the glassware. Glasses that have been kept in cardboard boxes may cause a wine to taste musty. When cleaning glassware, reduce the amount of detergent to a minimum, as soap residue may affect the flavour and quality of the wine.