Volatile Acidity in Wine: Causes, Detection, and Prevention

What Is Volatile Acidity?

Volatile acidity (VA) refers to the steam-distillable acids in wine, with acetic acid being the primary component. Unlike fixed acids such as tartaric and malic acid that provide pleasant tartness, volatile acids evaporate at room temperature and contribute a sharp, pungent aroma that at elevated levels is unmistakably vinegar-like.

Every wine contains some VA — it is a natural byproduct of fermentation. The issue is concentration. At very low levels (below 0.3 g/L), VA adds a subtle lift and perceived complexity. Between 0.3-0.7 g/L, it becomes increasingly noticeable to trained palates. Above 0.7-0.8 g/L, most people detect an unpleasant vinegar or nail polish character. The legal limit for commercial wines in the United States is 1.2 g/L for red wines and 1.1 g/L for white wines.

The Chemistry Behind VA

Acetic acid forms through several pathways. Acetobacter bacteria oxidize ethanol to acetic acid in the presence of oxygen. Certain yeast strains produce small amounts during fermentation. Lactic acid bacteria can produce acetic acid during malolactic fermentation, especially from residual sugar. Additionally, acetic acid reacts with ethanol to form ethyl acetate, an ester that at low levels smells fruity but at high levels produces a harsh nail polish remover aroma.

The interaction between acetic acid and ethyl acetate determines the overall sensory character of VA. A wine can have elevated acetic acid that is partly masked by its ethyl acetate form, or vice versa. Both must be considered when evaluating VA problems.

Detecting Volatile Acidity

Sensory Assessment

The most accessible detection method is your nose. Pour a sample and sniff at the rim of the glass. Acetic acid presents as a sharp, vinegar-like pungency. Ethyl acetate presents as a solvent, nail polish, or varnish-like quality. Both can be present simultaneously.

A useful trick is to warm the sample slightly in your hands — VA becomes more volatile and easier to detect at warmer temperatures. If you suspect VA but are not certain at room temperature, warming the glass may confirm your suspicion.

Laboratory Testing

For precise measurement, test using a Cash still distillation setup or a consumer-level VA test kit. The Vinmetrica SC-200 or SC-300 analyzer can measure VA with reasonable accuracy for home use. These devices distill the volatile acids from the wine and then titrate the distillate with sodium hydroxide.

Aeration-oxidation (AO) testing is the professional standard but requires specialized equipment. For most home winemakers, a combination of sensory evaluation and a basic test kit provides sufficient information.

Distinguishing VA from Other Acidities

VA is distinct from titratable acidity (TA), which measures all acids in wine and is dominated by fixed acids like tartaric and malic. A wine can have high TA and low VA (sharp but clean) or moderate TA and high VA (moderate body but vinegary). Testing both separately gives a complete acid profile.

Causes of Elevated Volatile Acidity

Acetobacter Contamination

Acetobacter is the primary villain in VA production. This genus of aerobic bacteria converts ethanol to acetic acid but requires oxygen to function. Every winery — home or commercial — has Acetobacter present in the environment. It becomes a problem when three conditions converge: the bacteria are present, oxygen is available, and sulfite levels are inadequate.

Fruit flies (Drosophila) are notorious vectors for Acetobacter. A single fruit fly landing on your must can introduce enough bacteria to produce significant VA if conditions favor growth. This is why covering your fermentation vessel during primary is essential even though CO2 production provides some protection.

Oxygen Exposure

Since Acetobacter is an obligate aerobe (it requires oxygen), minimizing oxygen exposure during and after fermentation is the most effective prevention. Headspace in carboys, leaky seals, dried-out airlocks, and prolonged exposure during racking all provide the oxygen Acetobacter needs.

Lactic Acid Bacteria

Lactic acid bacteria (LAB), particularly species of Lactobacillus and Pediococcus, can produce acetic acid as a byproduct of their metabolism, especially when fermenting residual sugar. This is distinct from the desirable malolactic fermentation carried out by Oenococcus oeni, which primarily converts malic acid to lactic acid with minimal VA production.

If LAB contamination occurs before or during primary fermentation — or if the wrong species dominate during MLF — VA can increase significantly. Wines with residual sugar are particularly vulnerable because LAB can ferment sugar via a heterolactic pathway that produces acetic acid alongside lactic acid and CO2.

Yeast-Derived VA

All yeast produces some acetic acid during fermentation. Most strains produce well under 0.3 g/L, but stressed yeast, high-sugar musts, and extreme temperatures can increase production. Wild yeast species, particularly certain strains of Kloeckera and Hanseniaspora, can produce elevated VA during the early stages of spontaneous fermentation before cultured Saccharomyces takes over.

Stuck Fermentation

A stuck fermentation with residual sugar creates an ideal environment for VA production. The sugar feeds bacteria, the wine lacks the protective effect of active CO2 production, and if the winemaker does not maintain sulfite levels, spoilage organisms flourish.

Treatment Options

Blending

The most practical home remedy for moderate VA is blending the affected wine with a clean, low-VA wine. The goal is to dilute the acetic acid and ethyl acetate below the sensory threshold. Conduct bench trials to determine the required ratio. A wine at 0.8 g/L VA blended 1:1 with a wine at 0.3 g/L VA yields approximately 0.55 g/L — potentially acceptable.

Reverse Osmosis and Membrane Technologies

Commercial wineries use reverse osmosis and evaporative pernerstorfer systems to physically remove acetic acid from wine. These technologies are generally not available to home winemakers, but some custom crush facilities offer the service for a fee. If you have a large batch of otherwise excellent wine with excessive VA, it may be worth investigating this option.

Microbial Stabilization

Regardless of other treatments, you must stop further VA production by eliminating the organisms responsible. Add potassium metabisulfite to maintain free SO2 at 35-50 ppm based on pH. If the wine is finished fermenting, adding potassium sorbate at 1/2 teaspoon per gallon in conjunction with sulfite prevents refermentation of any residual sugar by bacteria or yeast.

What Does Not Work

Do not attempt to neutralize acetic acid with bases such as potassium bicarbonate or calcium carbonate. These neutralize fixed acids, not volatile acids, and adding them will raise pH without effectively addressing the VA, potentially making the wine more vulnerable to further spoilage.

Prevention Protocol

Sulfite Management

Maintain appropriate free SO2 levels from the moment fermentation ends. At pH 3.4, target 30-35 ppm free SO2. At pH 3.6 and above, target 40-50 ppm. Test regularly and replenish as needed. SO2 is the single most effective tool against both Acetobacter and problematic LAB.

Oxygen Exclusion

Fill vessels completely, keep airlocks filled and functioning, and minimize the number of times you open or transfer wine. Use inert gas (CO2, nitrogen, argon) to blanket wine surfaces when topping up is not possible. Rack with the siphon outlet below the surface to prevent splashing.

Fruit Fly Exclusion

Cover all fermentation vessels with fine mesh or cloth secured with a rubber band during primary fermentation. Use fruit fly traps (apple cider vinegar in a jar with a paper funnel) in your winemaking area. Never leave wine exposed to the open air for longer than absolutely necessary.

Sanitation

Clean and sanitize all equipment meticulously. Acetobacter forms biofilms on surfaces, particularly in scratches, seams, and crevices. Replace scratched plastic equipment. Soak tubing, racking canes, and valves in Star San or a similar no-rinse sanitizer before every use.

Temperature Control

Keep finished wine at cool temperatures (55-65°F / 13-18°C) during aging. Warm temperatures accelerate both microbial growth and chemical VA production. A cool cellar or temperature-controlled environment is a significant advantage.

Frequently Asked Questions

Can I make vinegar from wine with high VA?

Yes. Wine with excessive VA that is beyond rescue can be deliberately converted to vinegar by exposing it to air and adding a vinegar mother (a culture of Acetobacter). Wine vinegar takes 3-6 months to mature and can be an excellent culinary product.

Does malolactic fermentation increase VA?

When conducted properly with Oenococcus oeni on dry wine, MLF produces minimal VA (typically less than 0.1 g/L increase). However, if MLF occurs in wine with residual sugar or is dominated by Lactobacillus species, significant VA can result. Always ensure primary fermentation is complete before initiating MLF.

How do commercial wineries deal with VA?

Commercial wineries use reverse osmosis, strict sulfite protocols, inert gas systems, and sterile filtration. They also have laboratory testing capabilities that allow them to detect VA rises early and intervene before the problem becomes severe. Home winemakers can achieve comparable results with good sulfite management and oxygen exclusion.

Is any amount of VA acceptable?

Yes. VA below 0.3-0.4 g/L is normal and can even enhance wine by adding a sense of lift and aromatic complexity. Some wine styles — like certain traditional Barolos and natural wines — are prized for a hint of VA that adds character. Problems begin when VA exceeds 0.6-0.8 g/L.

Can I test VA without lab equipment?

Precise measurement requires a distillation setup or electronic analyzer, but you can perform a rough sensory assessment. If you can detect vinegar or nail polish character in a room-temperature sample, VA is likely above 0.7 g/L. If you can only detect it in a warmed sample, it is likely in the 0.5-0.7 g/L range.