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, low SO₂ levels kept above 0.5 mg/L molecular.

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 or the Cashner titration method. 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.

A simple "hot vs cold" titration (Ripper titration before and after heating) provides a rough VA estimate.

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