VA listed 12April 2004

Acetic acid production

Kramer, E. L., & Noonan, M . J. (2004). Sources leading to development of acetic acid in wine - And potential options for its control. The Australian and New Zealand Wine Industry Journal, 19(1), 39-44.

In a recent study of 3000 Australian wines analysed for volatile acidity 30% of the red wines had a VA in excess of 0.7 g per litre and 20% of the white wines were in excess of 0.6 g per litre.

In this paper the authors surveyed a number of American and New Zealand winemakers
regarding volatile acidity. While the main area of concern was post MLF barrel storage
significant levels of VA were also found in must pre fermentation and during the primary
fermentation. Lower levels were also found during MLF and due to other winemaking practices.

There are many wild yeast capable of producing acetic acid, some to quite high levels, during fermentation. These include Candida krusei, Candida stellata, Kloekera apiculata, Hansenula anomala. Other spoilage yeast include Zygosaccharomyces balii and Brettanomyces species.

The VA producing wild yeast are most likely to contribute to the development of VA early in the fermentation process.

Zygosaccharomyces balii can be a problem due to its high tolerance to ethanol and sulfur dioxide and its ability to establish itself in the winery. There is some question as to the amount of VA produced by this organism.

Brettanomyces while it is best known for the vinyl phenol content it produces in wine it is also capable of producing extremely high levels of acetic acid as well. It requires oxygen for the production of acetic acid.

Spoilage Lactic acid bacteria – Latobacillus . These are organism are normally associated with high pH musts and wines. pH levels below 3.5 are toxic to these organisms.

Acetic acid bacteria. Gluconobacter oxydans has a low tolerance to ethanol and prefers high sugar environments whereas Acetobacter aceti and A pasteurianus are highly ethanol tolerant. These organisms can be found at quite high levels in damaged fruit.

They are also capable of surviving under low concentrations of dissolved oxygen and are capable of growing rapidly when the wine is aerated.

In addition there is some evidence of non-microbiological acetate production in wine.

To minimise VA problems winemakers need to be aware of the risk factors and take steps to
minimise damage. These can be broadly categorised as high-risk musts, risky winemaking
techniques and post fermentation cellar storage

"High risk" musts are those with elevated sugar levels and pH > 3.5

Strategies to handle these would include:

monitoring pH and sugar concentrations during the growing season
applying sulphur dioxide to high-risk grapes during transport
reducing the pH to below 3.5 upon receipt at the winery
cold setting 24 hours with enzyme addition
juice pasteurisation
treating the juice with lysosyme if MLF not required

Risky winemaking techniques

Spontaneous and low-temperature fermentations may be more likely to experience higher rates of VA development than where cultured wine yeast are added.

The winemaker should consider using a wine yeast culture in the following:

botrytis infected grapes
in overripe must where Lactobacillus contamination is likely
if Candida krusei, Candida stellata are likely to grow at low temperatures.

In the cellar

As spoilage organisms will be present in the winery, hopefully at low numbers, steps
should be taken to prevent their proliferation. These would include:

thoroughly cleaning equipment after use
having a regular topping program
either cleaning or refilling empty barrels immediately
maintaining humidity level of around 70% to prevent the barrels drying out
minimising oxygen uptake during cellar activities.

Measuring dissolved oxygen levels during processing will help identify risky operations.

References