Acid and Sugar Acid and sugar are two apparently ‘masking’ components of wine flavour. Wines that have a high degree of residual sugar usually have a high acid level to ’round off’ the flavour, and to leave the mouth ‘clean’. Acid has an essential role in flavour and ‘finish’, and is also a major wine preservative. Acid also gives a wine its bright lustre. As wine ages, its acid and alcohol combine in a process known as esterification, which is responsible for the creation of some of the most desirable characters in older wines. Hence acidity gradually reduces, especially as some of it also precipitates out of the wine with proteins and tannins. Wines that lack acid are generally thin and short on the palate. They do not have the freshness or finish of wines with good acidity. Alcohol Alcohol is another important wine preservative, and makes a contribution to flavour. It is warm, spirity and very slightly sweet. More and more modern wines have alcohol levels in excess of 13.5%, so the effect of alcohol as a wine flavour and structural component is even more noticeable than ever. As for its effects as a stimulant… Sulphur Dioxide (S02) SO2 is both an anti-oxidant and preservative added to wine. When found in excess it makes a wine unpalatable to many, with an asphyxiating effect not unlike burned matches. SO2 is given the Food Additive Number 220. Tannin Tannin is a natural preservative extracted from the skins, the stalks and the seeds. Wood tannin can be extracted from fermentation or maturation in oak barrels. Tannin produces a bitter, puckering effect in the mouth. Good wines display a balance between fruit, acid and tannin level. Oak Oak characters add complexity, depth of flavour and structure to a wine. In barrels wine undergoes a slow oxidation and extracts oak flavours and characters. New casks are the most effective in imparting these features to wine. Most barrels are brought from France or the United States. Wood characters may resemble vanilla, toastiness, butter, biscuits, lemons and other flavours. They are increased with smaller, newer and younger barrels, and higher temperatures produce faster, but not necessarily more desirable, results. Volatile Acidity Volatile acidity refers to the presence of a number of chemicals produced in wine as a results of microbiological spoilage, during or after fermentation. Acetobacter are the bacterial strain most commonly responsible for the problem. Volatile acidity is also recognised as a consequence of less than perfect winery hygiene, i.e. the possible presence and use of a dirty pump, filter, tank, etc. The most noticeable flavours are vinegar (acetic acid), nail polish-remover (acetone), and aeroplane glue (ethyl acetate). Some wines, some vintages of Grange Hermitage for instance, are deliberately oxidised to a small degree in the barrel to generate low levels of volatile acidity in order to ‘lift’ the nose or bouquet of the wine. Hydrogen Sulphide (H2S) Not to be confused with SO2, H2S is another by-product of microbiological spoilage known more commonly as rotten-egg gas. Its presence in wine indicates that it will only get worse. Hydrogen sulphide can result from an over-liberal dosage of elemental sulphur in the vineyard as a fungicide. If fermentation then gets out of control, perhaps through excessive heat, this sulphur can be converted to sulphide compounds. H2S can also occur in wine that has been kept in contact with wine lees or yeast/solids deposits for too long either in tank or in barrel. Winemakers adopting the new Australian trend (which is a traditional French technique) of keeping red wines in contact with the fermentation lees and skins after the fermentation must beware of the danger of H2S . H2S is a precursor of mercaptans, which have strong unpleasant spoilage aromas.
