Volatile Acidity (VA): Causes, Detection, and Fixes

Volatile acidity (VA) is the term for acids in wine that can evaporate — primarily acetic acid (vinegar) and to a lesser extent ethyl acetate (nail polish remover). At low levels VA contributes complexity; at high levels it's a wine-killing fault. Understanding it, preventing it, and catching it early is one of the most important skills in winemaking.

What Is Volatile Acidity?

Acetic acid (CH₃COOH) is the main component of vinegar. In wine it is produced by:

• Acetobacter bacteria, which oxidise ethanol to acetic acid in the presence of oxygen
• Lactic acid bacteria (LAB), which can produce acetic acid during fermentation or MLF
• Yeast — all yeast produce trace amounts of acetic acid as a normal fermentation byproduct

Ethyl acetate is produced when acetic acid reacts with ethanol (an esterification reaction). It has a nail polish remover / solvent smell. Ethyl acetate forms when acetic acid levels rise.

The fix relationship: VA is measured as "volatile acidity" in g/L of acetic acid equivalent. Ethyl acetate is separate but related — you smell it at low VA levels before the vinegar smell becomes apparent.

Legal and Threshold Levels

EU legal maximum: 1.2 g/L for reds, 1.08 g/L for whites (as acetic acid).

Note: tannins, sugar, and fruit concentration can mask VA somewhat. A very rich, fruity red might tolerate 0.7 g/L where a delicate white would be ruined at the same level.

Causes of Elevated VA

1. Acetobacter

The most common culprit. Acetobacter requires oxygen to produce acetic acid — it is an obligate aerobe. It enters wine via:

• Unclean equipment surfaces
• Fruit flies (which carry acetobacter on their bodies) — keep vessels covered
• Extended exposure to air during slow fermentation
• Poorly fitted airlocks or bungs

Prevention: Full sanitisation, sealed airlocks, avoiding oxygen exposure, and molecular SO₂ kept at or above 0.5 mg/L.

2. LAB (during fermentation)

Under some conditions, particularly with wild LAB or very low-YAN musts, bacteria produce significant acetic acid from residual sugars. Most likely in:

• Stuck fermentations with residual sugar (LAB love sugar too)
• Very low-acid musts (high pH, which favours LAB growth)
• Wines with insufficient SO₂

3. Yeast stress

All fermentations produce some acetic acid — typically 0.2–0.4 g/L. Yeast under stress (nutrient deficiency, temperature shock, high alcohol, high osmotic pressure) produce significantly more:

• High-sugar musts without adequate nutrients
• Fermentation starting very warm
• Temperature spikes during active fermentation

4. Brett (Brettanomyces)

Brett produces both acetic acid and ethyl acetate as part of its metabolic activity. A wine showing "barnyard" and "nail polish" together may have a brett problem rather than pure acetobacter.

Testing for VA

Smell

The most immediate indicator. Sniff the airlock gas during fermentation — if it smells vinegary, check immediately. In finished wine, swirl and smell: acetic acid is sharp and rises from the glass. Ethyl acetate smells like acetone/nail polish and is usually detected first.

Taste

Volatile acidity creates a sharpness on the back palate and nasal passage during swallowing (the "volatile" part — it literally evaporates through the nasal passages).

Titration test

Volatile acidity is measured by steam distillation — the acetic acid is separated from the wine's fixed acids in a Cash still and the distillate is then titrated with standardised NaOH. Home VA test kits (e.g. CHEMetrics VA test kit) are available and give reasonable accuracy (±0.05 g/L). Results are expressed in g/L of acetic acid.

There is no reliable way to measure VA with a simple bench titration at home: because VA is only a small fraction of total acidity, you have to physically separate it by distillation first. If you need a number, use a distillation-based lab test or the dedicated VA test kit above rather than trying to infer it from an ordinary acidity titration.

Can You Fix High VA?

The honest answer: high VA is essentially irreversible at home. There are commercial treatments that can reduce it slightly, but none are practical for home winemakers.

Commercial interventions (not available at home)

• Reverse osmosis (RO): VA molecules pass through membranes and are removed. Used in commercial wineries.
• Ion exchange: removes acetic acid. Complex equipment.
• DEAE-cellulose filtration: experimental, rarely used.

What you can actually do

If VA is below 0.6 g/L:

• Add SO₂ to inhibit further acetobacter activity
• Rack immediately to remove any lees that may be harbouring bacteria
• Seal the vessel tightly and eliminate all headspace
• Consider blending with clean wine at a ratio that brings VA below the detection threshold

If VA is 0.6–0.8 g/L:

• Same as above
• The wine may still be acceptable in a blend or if the style can accommodate it (some aged natural wines, some oxidative styles)
• Consider using for cooking if the flavour profile doesn't suit drinking

If VA is above 0.8 g/L:

• The wine is probably a vinegar. The realistic options are:
  • Let it finish converting to vinegar (actually make proper wine vinegar)
  • Distil it (if legally permitted in your jurisdiction) to recover alcohol
  • Discard it

Blending for dilution

If VA is marginal (0.6–0.7 g/L), blending with a large proportion of low-VA wine can reduce the combined VA to below threshold. This is a legitimate commercial technique.

Prevention Is Everything