Understanding Volatile Acidity

One of the things I've noticed about wine makers is that when they taste a wine they tend to evaluate it for faults, not for merits. To me, this seems a little backwards. My philosophy is that a wine, like people can have faults, but still be worthwhile, even enjoyable. Then again, its their job to asses wines in order to produce the best possible product. But every so often I come across a wine that is, in fact, faulty. Most often it's "cork taint", or TCA. But there are other, less common faults in wine. I recently came across a wine that I thought had a touch of Volatile Acidity on the nose. I was a turned off, and sadly I could not recommend what could have been a great wine. Everything else was fetching, but the nose was unpleasant.
So what is VA? Where does it come from? Volatile Acidity is primarily acetic acid, as in vinegar, and ethyl acetate, which smells like nail polish remover or paint thinner. It can develop throughout the wine production process though aerobic yeasts. That means that excess oxygen during fermentation can encourage microbial activity that causes VA. Jamie Goode's site, the Wine Anorak gives a good description of VA's role in a wine:

Volatile acidity (VA) is caused by naturally occurring chemicals in wine, produced by the actions of acetic bacteria. It can be shown that there are measurable levels of VA in all wine. (Emphasis mine) VA is split between two types of chemical – acetic acid and ethyl acetate. Rightly or wrongly, I tend to think of the acetic acid affecting the taste with the sourness or edge to a wine which recalls vinegar, with the ethyl acetate leading to various volatile traits from a mild ‘lift’ to the nose which isn’t directly noticeable, through a boot polish kind of aroma, to nail varnish remover in the worst cases. The fact is that acetic acid and ethyl acetate are formed together and such a distinction may not in fact be so straightforward. But then that’s wine for you – it is more than likely that a complex picture of elements are involved in whether we perceive an issue or not. In the case of VA, it’s not just the level – but also the wine style and type. The richer, bigger wines (Port, for example) can carry greater amounts of VA without detriment. In fact, the sweet dessert wines styles affected by noble rot actually seem to need high levels of VA in order to help form the nose. Without these more volatile elements, the heavy, sugary wine would not give much on the nose at all, and the VA provides an essential ‘lift’ to bring the less volatile elements to our nose.

Whats important to note is that acetic acid and ethyl acetate are produced during fermentation and therefore present in all wines. Perception thresholds are different from person to person, and from wine to wine. It is when these elements are in excess, i.e. out of balance with the rest of the wine, that they becomes perceptible and unpleasant. Think of wine as a harmonious, yet complex network of elements, each must be weighted proportionally to the others.

In this light, VA is not a fault, it is an integral part of the wine. Rather, the fault is that the wine is not in balance. The wine I came across suffered from this problem. What I experienced on the palate was a wine that displayed interesting fruit and development, but on the nose had excess VA in proportion to its other aromas.