Volatile Acidity

Abstract

The total acidity of a wine is the result of the contribution of nonvolatile or fixed acids such as malic and tartaric plus those acids separated by steam volatilization. A measure of volatile acidity is used routinely as a indicator of wine spoilage (see Table 5-1). Increases are usually attributed to microbial production of certain low molecular weight acids and their esters. Although generally interpreted as meaning acetic acid content (in grams per liter), a traditional volatile acid analysis includes all those steam-distillable acids present in the original wine sample. Thus, significant contributions to the volatile acid content may be made by carbon dioxide (as carbonic acid), sulfur dioxide (as sulfurous acid), and, to a lesser extent, lactic, formic, butyric, and propionic acids. In addition, sorbic acid (added to wine as potassium sorbate), used as a fungal inhibitor, is also steam-distillable and should be taken into consideration when appropriate. The contributions of CO₂, SO₂, and sorbic acid interferences can be seen in Table 5-2.