Botrytis infected fruitMarch 8, 2019
Volatile acidity – What are the effects on my wine?
Dealing with a high volatile acidity wine? A brief summary of what volatile acidity is, why it is present in your wine and what steps should be taken to minimize the effects follows.
What is volatile acidity and why is it in my wine?
Volatile acidity is an important sensory parameter, with higher levels indicating wine spoilage. The main component of volatile acidity is acetic acid, which has a vinegar-like aroma. Under normal winemaking conditions yeasts produce acetic acid at levels ranging from 0.3 – 0.5 g/L during alcoholic fermentation. Levels of 0.15 – 0.30 g/L are then further produced by lactic acid bacteria during malolactic fermentation. VA levels after the successful completion of both alcoholic fermentation and malolactic fermentation are generally lower than 0.60 g/L.
Elevated levels of volatile acidity are frequently attributed to the presence of spoilage bacteria; such as Lactobacillus, and Acetobacter.
Lactobacillus may use residual sugar, tartaric acid and glycerol to produce acetic acid. Lactobacillus populations present during primary fermentations may utilize residual glucose and fructose in the wine to produce acetic acid, sometimes to the point where it is toxic to yeast resulting in a stuck fermentation.
In aerobic environments, acetobacter and surface film yeasts can utilize sugars or oxidize ethanol to produce acetic acid. Acetobacter require oxygen for growth and will continue to grow in environments containing even the slightest bit of oxygen, including oak barrels. Half full tanks are highly at risk of acetobacter growth, where growth may occur on the surface of the wine and contaminate the whole volume of wine. Acetobacter growth can, therefore, be prevented by keeping wine storage containers full and by following strict barrel topping regimes.
When should I test for volatile acidity?
Volatile acidity can be measured at various stages of the winemaking process. The following are guidelines of when to test volatile acidity levels in wine, as this is when fluctuations in concentrations may occur;
- When tanks are not full
- After alcoholic fermentation
- After malolactic fermentation
- During stuck alcoholic and malolactic fermentations
- Periodically through wine storage
- When a film is found on a specific wine
How is volatile acidity tested?
Volatile acidity is generally measured as the steam distillable acids present in the wine, which includes acetic, butyric, formic and propionic acid. Acids other than acetic acid have a negligible contribution towards the volatile acidity levels present in the wine. Volatile acidity at Vinlab is either measured via FTIR (winescan) or distillation, with volatile acidity being expressed as g/L. Acetic acid can be measured enzymatically or via HPLC. Although this should yield the same result as volatile acidity, certain countries insist on the volatile acidity result expressed as only acetic acid.
My wine has a high volatile acidity, now what?
High volatile acidity wines are easier to prevent than remediate, as it is often the result of over-exposure to oxygen and poor sulphur dioxide management. Management of most wine-tolerant micro-organisms is possible through proper sulphur dioxide treatments, adequate temperature control, good cellar sanitation practices, and appropriate oxygen management strategies.
Spoilage microbes are less tolerant to lower pH levels with growth being encouraged at pH levels above 3.60. Low pH wines also ensure free molecular SO2 is most effective. Making acid adjustments early in the winemaking process aid in maintaining a wine that has optimal microbiological stability, encouraging wines with lower pH’s and ensuring the effectiveness of the free molecular SO2 present.
If intervention throughout cellaring was not taken, and volatile acidity levels continued to rise, blending with a lower volatile acidity wine is an option. Both the wine used for blending and the “contaminated” wine should be sterile filtered before blending preventing any further microbial spoilage resulting in increases in volatile acidity.
When volatile acidity levels cannot be rectified with blending, reverse osmosis is always an option to remove these high concentrations of acetic acid. Following reverse osmosis, the wine can be blended with a low volatile acidity wine. This low volatile acidity wine must be sterile filtered before blending, as well as, the “contaminated” wine.
Will volatile acidity levels present in my wine be sensorially detected?
VA can be sensorially detected
at concentrations above approximately 0.8 g/L
. Limits of volatile acidity are legally defined. Legal limits
defined by SAWIS can be seen in the table that follows (table 1).
Table 1: Legal limits of Volatile acidity (SAWIS)
|Noble late harvest||<1.8 g/L|
|Wine from naturally dried grapes||<1.8g/L|
|Bulk wine for export||<0.8g/L|
|All other wines||<1.2g/L|