Noemie Breton, œnologist
What is it?
In the world of œnology, there is much debate about Volatile Acidity. Some have learned to live with it while others would much rather avoid it. Through this article, learn more about Volatile Acidity.
Volatile Acidity is an essential parameter in œnology. It has a strong influence on taste and wine aroma. As its name implies, it refers to acids which have a tendency to evaporate easily. In small amounts, it adds freshness and vivacity to wine but if present in high concentrations, it quickly becomes a fault as the wine is turning into vinegar.
In wine, acetic acid is the main constituent of Volatile Acidity. Ethyl Acetate is also a component of Volatile Acidity but in very small quantity. Increasing amounts of acetic acid will lead to Ethyl Acetate formation. This will cause nail polish and glue-type aromas.
Acetic acid and Ethyl acetate concentrations are influenced by many factors such as the type of winemaking, winery hygiene and aging conditions.
Legal limits may vary from country to country. In Canada, the legal limit for Volatile Acidity in wines is 0.98 g Sulfuric Acid eq/L and up to 1.64 g Sulfuric Acid eq/L in ciders.
Enzymatic analysis of acetic acid is an excellent way to measure Volatile Acidity. Our colleagues, Laboratoires Dubernet, showed that there is no significant differences in the results obtained by enzymatic analysis and the OIV distillation method.
Volatile Acidity, where does it come from?
1-Fermentation
During alcoholic fermentation, Saccharomyces cerevisiae yeasts generate acetic acid in low quantities as a natural by-product of sugar transformation to ethanol. However, if the alcoholic fermentation is poorly controlled, acetic acid can be produced in undesired higher levels.
Several factors must be considered and monitored to prevent an increase in Volatile Acidity:
- Nitrogen deficiency : Nitrogen deficiency will cause undue stress to yeasts and will lead to yeasts producing more acetic acid.
- Uncontrolled temperature : High temperatures during alcoholic fermentation will favor growth of spoilage bacteria which are high producers of acetic acid.
- Sluggish fermentation : A sluggish fermentation often occurs when levels of bacteria are high compared to yeasts levels. Spoilage bacteria will ferment sugars giving rise to high level of acetic acid and acetaldehyde.
2-Lactic Bacteria Developpement during Alcoholic Fermentation : Lactic Spoilage
Lactic bacteria are normally involved in malolactic fermentation as they convert malic acid into lactic acid. However, during uncontrolled alcoholic fermentation, bacteria can develop more rapidly and transform fermentable or residual sugars into acetic acid. This results in an undesired increase in volatile acidity. This is known as lactic spoilage.
Lactic spoilage occurs when various parameters are poorly controlled during alcoholic fermentation:
- - Presence of residual sugars during an incomplete or sluggish fermentation.
- - pH higher than 3.5
- - High temperature (around 25 degrees Celsius)
- - Poor cellar hygiene leading to bacteria developpement
3-Presence of acetic bacteria during ageing : Acetic Spoilage
Acetic bacteria need oxygen to thrive. In presence of oxygen, acetic bacteria will convert ethanol in acetic acid and acetaldehyde (ethanal). Volatile acidity will increase as a result. This is Acetic Spoilage.
To limit acetic bacteria growth, cellar hygiene is critical. Exposure of wine to oxygen must be kept at a strict minimum. It is important to note that acetic bacteria are less sensitive to SO2 than lactic bacteria.
How to prevent appearance of Volatile Acidity?
Regular monitoring during each winemaking step is critical to prevent Volatile Acidity apparition and to ensure wine quality.
Maintaining good control during winemaking, keeping oxygen exposure to a minimum and managing SO2 levels consistently are key factors to keeping Volatile Acidity to a minimum.
The OENOSCIENCE Laboratory professionals can assist you through regular monitoring during the winemaking process. This will help you manage risks and avoid costly situations. You have comments or suggestions? You would like to discuss specific topics in œnology?
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