White Wine Oxidation: Why Your Chardonnay Turned Brown (And How to Prevent It)

Your Chardonnay looked golden in the carboy. Now it is brown. Oxidation has struck—the most common problem in white wine production. Here is why it happens and how to prevent it.

Why White Wine Oxidizes

White wines lack the protective antioxidants present in red wines. Red grape skins contribute tannins and anthocyanins that absorb oxygen. Whites, pressed before fermentation, have no such protection.

Polyphenol oxidases (enzymes) in grape must catalyze browning reactions when oxygen is present. The same chemistry that turns a cut apple brown turns your Chardonnay amber.

When Oxidation Happens

At crush: Exposed must browns quickly as enzymes work. This is the most critical time.

During fermentation: Active fermentation produces CO2 that protects wine. Oxidation risk is lower.

Post-fermentation: Once fermentation stops, protection disappears. Wine in half-full carboys oxidizes rapidly.

During racking: Each transfer exposes wine to air.

At bottling: Improper technique introduces oxygen that causes browning over time.

Prevention at Crush

• Add SO2 immediately: 50-75 ppm at crush inhibits oxidative enzymes
• Work quickly: Minimize time between crushing and pressing
• Chill must: Cold temperatures slow enzymatic oxidation
• Consider ascorbic acid: Added with SO2, it provides additional protection
• Avoid aggressive pressing: Gentle pressing limits phenolic extraction

Prevention During Aging

• Top up vessels: Never leave significant headspace
• Maintain SO2: Regular additions keep free SO2 at protective levels (25-35 ppm)
• Minimize racking: Each rack introduces oxygen. Rack only when necessary.
• Use inert gas: CO2 or nitrogen to purge headspace before sealing
• Check airlocks: Dried-out airlocks let air in

Signs of Oxidation

• Color shift from pale yellow to gold to brown
• Loss of fruity, fresh aromas
• Nutty, sherry-like notes (inappropriate in table wine)
• Flat, lifeless palate

Can Oxidized Wine Be Saved?

Mild oxidation: May be masked by blending with fresh wine. The oxidized character does not disappear but can become less obvious.

Moderate oxidation: Wine is permanently compromised. Consider using for cooking or vinegar production.

Severe oxidation: The wine is undrinkable. Learn from it and move on.

The Ascorbic Acid Question

Ascorbic acid (vitamin C) is a powerful antioxidant but reacts with oxygen quickly, eventually producing unpleasant compounds. It should always be used WITH sulfite, never instead of it. And once you start using it, you must continue throughout the wine’s life.

Hyperoxidation: Fighting Fire with Fire

Some winemakers intentionally expose must to oxygen before fermentation, allowing browning reactions to complete before protection. The brown compounds settle out, and the wine ferments cleaner. This counterintuitive technique requires experience to execute properly.