Chapter 19

Juice and Wine Acidity

Volatile Acidity in Wine

Volatile acidity (VA) is a measure of all volatile acids in wine and is measured and reported separately from TA because it is an important sensory quality parameter, with higher levels indicating wine spoilage. These acids can include: acetic acid (the main volatile acid in wine), lactic acid, formic acid, butyric acid, propionic acid, sorbic acid, carbonic acid, and sulfurous acid. Because acetic acid comprises the majority of the VA, it is expressed as acetic acid. From a qualitative standpoint, this value has always been, quite justifiably, linked to quality.

Sources of Volatile Acidity

The sources of volatile acidity in wine are the grapes from which it is made, the fermentation process, the maturation process, and yeasts and/or bacteria which may play a role during this process. Diseased grapes affected by Botrytis will have a higher volatile acidity. Native or wild yeasts such as Hansenula and Kloeckera can produce high concentrations of acetic acid before and during the early stages of fermentation.

Threshold Levels

The question of how much VA is normal and acceptable in a wine is subjective, largely influenced by wine style and consumer acceptance. Ribereau-Gayon et al. (2006b) indicate that VA is not easily detected below 0.72 g/L, but above this level wine aroma starts to be affected and flavor starts to deteriorate, such that at acetic acid levels of 0.90 g/L and above, the wine has a noticeable harsh, bitter, and sour aftertaste. Volatile acidity is more easily detected if a small amount of ethyl acetate is also present, and in some cases ethyl acetate aroma can dominate.

Analyzing Volatile Acidity

There are several techniques of varying complexity that are used to measure the concentration of volatile acidity in wine. Some of the methods include team distillation (using a Cash still), enzymatic assay, and high-performance liquid chromatography (HPLC).

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