WinemakerOS

What Is Volatile Acidity?

Volatile acidity (VA) refers to the gaseous acids in wine that can evaporate at room temperature. The primary component is acetic acid — the same compound that makes vinegar smell like vinegar. Ethyl acetate, a related compound that forms when acetic acid reacts with ethanol, contributes a sharp nail-polish or solvent aroma even at lower concentrations.

All wines contain some VA. The question is whether it is at a level that detracts from quality. Legal limits in the US are 1.2 g/L for red wines and 1.1 g/L for whites, but sensory thresholds are typically much lower — most tasters notice VA at 0.6–0.8 g/L in whites and 0.8–1.0 g/L in reds. A well-made wine should sit well below 0.6 g/L.

What Causes High Volatile Acidity

VA is produced by microorganisms — primarily acetic acid bacteria (AAB) and, to a lesser extent, certain wild yeasts and lactic acid bacteria. The conditions that encourage VA production are predictable:

Oxygen exposure: Acetic acid bacteria are aerobic. Any wine sitting with headspace, a loose bung, or a cracked tank seal is at risk. This is the most common cause in small wineries.
Stuck or sluggish fermentations: When fermentation slows or stops with residual sugar still present, wild yeasts and bacteria have time to metabolize that sugar into acetic acid rather than ethanol.
Poor sanitation: Contaminated equipment, dirty hoses, or a barrel that was not properly cleaned after a previous lot can introduce AAB directly into a new batch.
Low free SO₂: Sulfur dioxide inhibits spoilage organisms. Wines that have drifted low on molecular SO₂ — especially at higher pH — are vulnerable even after a clean fermentation.
High pH grapes: AAB and spoilage organisms thrive at higher pH. Grapes coming in above 3.6 give these microbes a friendlier environment and require tighter management throughout winemaking.

How to Measure VA

The standard method for measuring VA is steam distillation followed by titration, often called a Cash still or Segmented Flow Analysis (SFA) in a lab setting. If you are sending samples to an outside lab, VA is one of the most useful panels to run at three points: post-fermentation, at first racking, and before bottling.

For in-winery monitoring without a full lab setup, enzymatic test kits (available from suppliers like Scott Labs and Vinquiry) can give you a directional reading. They are not as precise as steam distillation, but they are fast and good enough to flag a wine that is trending upward between lab checks.

Keep a running log of VA readings for each lot. A single reading tells you where you stand. A series of readings tells you whether a wine is stable or climbing — which is far more actionable information.

Prevention Is Cheaper Than Treatment

Once VA is in a wine, your options are limited and expensive. Prevention is where small winemakers should focus most of their energy.

Maintain SO₂: Test free SO₂ regularly and adjust additions to keep molecular SO₂ at 0.5–0.8 mg/L (the effective inhibitory range). At pH 3.6, you need more free SO₂ to hit that molecular target than you do at pH 3.3. Use a calculator — do not guess.
Minimize headspace: After racking, keep containers full. Use inert gas (argon or nitrogen) to top off before bunging. If you must leave headspace briefly, blanket it with CO₂.
Top barrels on schedule: Wine evaporates through oak. A barrel that drops an inch or two below the bung over a few weeks is an open invitation for AAB. Build a topping schedule and stick to it.
Complete fermentations cleanly: If a fermentation is struggling, address it immediately. Add nutrients, adjust temperature, or inoculate with a fresh yeast starter. Do not let it limp along with sugar sitting around.
Sanitize everything that touches wine: Hoses, pumps, racking wands, tanks, and barrels. Acetic acid bacteria can survive in residual wine films on equipment surfaces. Rinse with SO₂ solution before use.

What to Do If VA Is Already Elevated

If a wine has climbed to a problematic level, you have a few options — none of them perfect:

Blending: Diluting a high-VA wine with a clean, low-VA wine is the most common practical approach. The blended result must be checked to ensure it stays below sensory and legal thresholds.
Reverse osmosis (RO): Commercial wineries use RO to strip VA directly from wine. The process works, but the equipment is expensive. Some custom crush facilities or mobile services offer this.
Vacuum evaporation: Similar principle to RO — removes volatile compounds under reduced pressure. Also requires specialized equipment.
Accepting the loss: If a wine is above 1.2 g/L and cannot be blended down, it cannot be sold as wine in the US. At that point, repurposing as vinegar or distillation stock may be the most honest path forward.

Tracking VA Across Lots

One of the practical challenges in small wineries is keeping VA data connected to lot records over time. A reading taken at pressing is only useful if you can compare it to the reading at six months in barrel. Without a consistent tracking system, those data points live in different spreadsheets, notebooks, or memory — and the trend line disappears.

Building VA tracking into your lot management workflow — rather than treating it as a one-off lab result — is one of the highest-value operational changes a small winery can make. When something goes wrong, you want to know exactly when VA started moving and what happened in the cellar around that time.