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Volatile Acidity

Volatile Acidity: What is it? and how do I stop it?

Volatile acidity (VA) is defined as the steam distillable acids found in wines. Acetic acid is the biggest contributor to VA, but lactic, formic, propionic and butyric acid can also be culprits. Volatile acidity can plague any wine; changing the characteristics of wine from an award winner to vinegar in a matter of weeks. It not only effects the aroma and the flavor, but can also be illegal in high quantities. The bad news is that removing volatile acidity from a wine is costly and not 100% treatable, but the good news is that it is easily preventable. 

Let’s start with the basic microbiology to learn exactly what is going on in the wine: 

Microbial Level
Acetic acid is typically the largest component of volatile acidity, it is caused by bacteria (Acetobacter aceti) that can be found everywhere: grape skins, fruit flies, barrels, and other surfaces in the cellar. The bacteria converts ethanol to acetic acid and produces ethyl acetate as a byproduct of the conversion. Ethyl acetate has a nail polish characteristic in high quantities, not a nice addition to the vinegar characteristics of acetic acid. 

Microbes in general reproduce rapidly, but with the wrong environment, their growth can increase exponentially. The two conditions that expedite the growth are warm temperatures and oxygen. Depending on what methods and equipment you are using in the cellar, sometimes fluctuation of temperature and oxygen exposure are unavoidable during the winemaking process. This can expose your wine to acquiring volatile acidity in the most delicate steps of the wine's life: receival of grapes, primary fermentation, malolactic fermentation, and barrel aging. The abundance of bacteria found in a high VA wine make it easily transferable from wine to wine. 

As a side note, Brettanomyces also produces acetic acid. To find out more information about Brett, see our previous article about Brett and testing for it through PCR analysis

Prevention
The best prevention is to test your wine for volatile acidity. Monitoring the VA in your wine will allow you to learn if there are any changes in your VA levels. In having your VA results on record, it is easier to pinpoint a problem. 

It is also important to limit the air exposure of your wine to ensure bacterial growth stays at a minimum. Check that your bungs are tightly placed in the barrels and your wine is constantly topped. Be sure all surface areas of the cellar are clean to avoid spreading the bacteria, sanitize all winemaking equipment and consciously clean all surfaces in which wine touches. Dirty racking and sampling valves are easily missed, but can become an issue if not properly cleaned or sprayed with an SO2 or ethanol solution when used. It is also important to stay on top of your sulphur levels, as sulphur acts as a preventative for microbial activity. 


Solutions 
If your wine has unfortunately acquired VA during some point in the winemaking process, there are a few solutions to limit the sensory expression: 

Reverse Osmosis: Reverse Osmosis for VA is a procedure where the high VA wine is passed through a very fine filter, thus separating the water, acetic acid, and alcohol from the remainder of the wine. The acetic acid is then extracted from the water/alcohol solution, and the water/alcohol is added back to the wine. Although expensive, some manufacturers claim that reverse osmosis will eliminate up to 50% of VA found in the wine. 

Blending: Blending a high VA wine with a low level VA wine can help reduce the sensory effect. If proceeding with this route, be sure to limit the conditions that encourage bacterial growth. Limiting acetic bacteria growth will help prevent the volatile acidity from coming back and overpowering your blend. 

Embrace it: In fact, some older Italian wines have high VA levels. Just keep in mind, the US limit of volatile acidity in a wine is 1.4 g/L for red wines and 1.2 g/L for whites. 

For questions or to order a volatile acidity test, contact The Lab Pros today: 




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