Organic Acids in Wine

At harvest time, the main acids found in the berries are tartaric and malic, and, in minor amounts, citric acid. Succinic, lactic and acetic acids present in wine mainly result from alcoholic or malolatic fermentation. The acid content of grapes should fall in the range from 0.65 to 0.85 g/100 ml (%).
The pH of wine grapes is one of the most important and controversial quality parameters for grape quality and the wine-making industry. The pH value of the wine reflects the amount and the strength of the acids, and the effects of minerals and other materials present in the wine.
Wine pH depends upon three major factors:

• the total amount of acid present
• the ratio of malic acid to tartaric acid
• the quantity of potassium present

The importance of acidity in a wine:

• a wine too low in acid will taste flat and dull
• a wine too high in acid will taste too tart and sour
• acidity allows wine to maintain its freshness
• acidity has an impact on flavour components and color
• acid content in the berries and then in the must affect vinification and wine stability
• high acidity (pH 3-4) avoids the development of contaminating bacteria

The contribution of the various acids in wine:

• tartaric acid contributes the tart taste of wine, as well as to the biological stability and the longevity of wine
• malic acid is the most fragile wine acid and confers a green taste to the fruit and to the wine
• a decrease in malic acid content is achieved during malolactic fermentation (ML), when bacteria convert malic acid into lactic acid
• present in relatively small amounts, citric acid confers a fresh and slightly acid taste to wines
• the flavour of succinic acid is a complex mixture of sour, salty and bitter tastes
• lactic acid in wines confers a slightly sourish taste as it does in yogurts
• the high volatility of acetic acid makes wines less appealing to consumers, with unpleasant aroma and palate
• vinegar bacteria (Acetobacter) can produce large quantities of acetic acid from ethyl alcohol by an oxidation process, in the presence of large quantities of air

References:
1. Carlos Conde, Paulo Silva, Natacha Fontes, Alberto C. P. Dias, Rui M. Tavares, Maria J. Sousa, Alice Agasse, Serge Delrot, Hernâni Gerós, Biochemical changes throughout Grape Berry development and fruit and wine quality, Food, 1(1), 1-22 ©2007 Global Science Books.