Oxidation Management in White Wines: Prevention and Correction

Problem Definition

Oxidation in white wines causes browning, loss of fresh fruit character, development of stale/flat aromas, and premature aging. Unlike red wines where moderate oxidation can be beneficial, white wine quality typically depends on preventing oxygen exposure from crush through bottling.

Particularly susceptible styles:

Aromatic whites requiring fresh, varietal character (Grüner Veltliner)
Low-sulfur or “natural” wines
Wines with elevated phenolic content (skin-contact whites)
High-pH whites with reduced SO₂ efficacy

Deliberately oxidative styles (traditional Vouvray sec, Jura vin jaune) require different protocols not addressed here.

Technical Context

Oxidation Chemistry

White wine browning proceeds through enzymatic and non-enzymatic pathways:

Enzymatic oxidation (pre-fermentation):

Polyphenol oxidase (PPO) and laccase (from Botrytis) catalyze phenol oxidation
Substrates: Caftaric acid, catechins, other hydroxycinnamic acids
Products: Quinones → brown polymeric pigments
Prevention: Inactivate enzymes (SO₂, heat) or exclude oxygen

Non-enzymatic oxidation (post-fermentation):

Metal-catalyzed (Fe²⁺, Cu²⁺) oxidation of phenols
Direct oxidation by molecular oxygen
Products: Acetaldehyde, quinones, brown pigments
Slower than enzymatic; cumulative damage over time

Key Substrates

Compound	Role in Oxidation	Typical Concentration
Caftaric acid	Primary PPO substrate	50-200 mg/L
Catechins	Secondary substrate; contribute to browning	10-50 mg/L
Glutathione	Antioxidant; reacts with quinones	10-30 mg/L
Ascorbic acid	Antioxidant; regenerates glutathione	Added: 50-100 mg/L

Protective Compounds

Sulfur dioxide:

Inhibits PPO enzyme activity
Reduces quinones back to phenols
Binds acetaldehyde (prevents stale aromas)
Molecular SO₂ is active form; dependent on pH

Glutathione:

Grape-derived tripeptide
Reacts with quinones to form colorless adducts (GRP: Grape Reaction Product)
Higher glutathione = greater oxidation resistance
Can be lost during pressing and processing

Ascorbic acid:

Reduces quinones; regenerates glutathione
Requires SO₂ to prevent pro-oxidant cycling
Used as adjunct, not primary protection

Oxygen Exposure Points

Operation	Typical O₂ Exposure	Risk Level
Crushing	2-4 mg/L	High
Pressing	4-8 mg/L	High
Racking	1-3 mg/L	Moderate
Filtration	0.5-2 mg/L	Moderate
Bottling	0.5-3 mg/L	Moderate-High
Cork closure	1-4 mg/L/year	Cumulative

Options and Interventions

Protective Handling (Crush to Press)

SO₂ addition at crush:

30-50 mg/L for clean fruit
75-100 mg/L for Botrytis-affected fruit
Inhibits PPO; reduces quinones
Timing: Immediately upon crushing

Inert gas protection:

Blanket receiving hopper, press, tanks with N₂, CO₂, or Ar
Reduces dissolved oxygen in must
Critical for premium aromatic whites

Hyperoxidation (deliberate oxidation):

Expose must to oxygen before fermentation
Saturate and precipitate oxidizable phenols
Rack off brown sediment; ferment cleaner must
Produces stable but neutral wines; not for aromatic styles

Cold settling:

Chill must to 5-10°C; settle 12-24 hours
Reduces phenolic content (phenols settle with solids)
Cold also slows oxidation reactions

Fermentation and Aging

Reductive fermentation:

Minimize headspace; inert gas overlay
Fermentation CO₂ provides natural protection
Sur lie aging: Yeast release glutathione and reduce oxidation products

SO₂ management:

Add SO₂ immediately post-fermentation (30-50 mg/L)
Maintain free SO₂ at target (25-40 mg/L for whites)
Check frequently; consumption rate varies with wine chemistry

Temperature control:

Oxidation rate doubles per 10°C increase
Store whites at 10-14°C
Cold stabilization period also reduces oxidation

Bottling

Dissolved oxygen minimization:

Sparge wine with N₂ before bottling
Inert gas blanket in bottling line
Target: <1 mg/L dissolved oxygen at fill

Headspace management:

Minimize headspace volume
Inert gas flush (N₂, CO₂) before closure
Target: <2 mg/L headspace oxygen

Closure selection:

Screwcap (Saran or Saranex liner): Very low oxygen ingress
Technical cork (DIAM, Nomacorc): Controlled ingress
Natural cork: Variable; higher oxygen transmission

Trade-offs and Risks

High SO₂:

Effective oxidation protection
Legal limits apply (150-200 mg/L total for dry whites)
High bound SO₂ from aldehyde binding
Consumer preference for “low sulfite” in some markets

Hyperoxidation:

Stabilizes wine against future browning
Strips varietal aromatics and freshness
Not suitable for aromatic varieties or premium styles

Ascorbic acid:

Effective short-term protection
Without adequate SO₂, becomes pro-oxidant
May promote accelerated browning post-bottling if SO₃ depleted

Screwcap closures:

Excellent oxidation protection
May exacerbate reductive faults (VSCs)
Select appropriate liner oxygen transmission for wine style

Glutathione supplementation:

OIV approved additive in some jurisdictions
Effective when combined with inert handling
Cost consideration for large volumes

Practical Implications

Variety-specific considerations:

Chardonnay: Style-dependent. Reductive handling for Chablis minerality; controlled oxidation acceptable for barrel-fermented Bourgogne blanc. Bâtonnage redistributes lees antioxidants.
Chenin Blanc: High acidity provides pH advantage for SO₂ efficacy. Vouvray dry styles require careful protection; demi-sec and moelleux have residual sugar antioxidant effect.
Viognier: Prone to rapid oxidation; low natural acidity (high pH) reduces SO₂ efficacy. Requires rigorous inert handling and early bottling.
Grüner Veltliner: Wachau DAC style depends on freshness and minerality. Reductive handling standard; screwcap increasingly common.

Appellation-specific implications:

Chablis AOC: Reductive winemaking preserves mineral, flinty character. Stainless steel or neutral oak; minimal oxygen exposure. Screwcap adoption increasing.
Bourgogne AOC (white): Barrel fermentation introduces controlled oxygen; bâtonnage integrates lees protection. Oak tannin also provides antioxidant capacity.
Wachau DAC: Steinfeder and Federspiel styles require fresh aromatics. Smaragd (richer style) can tolerate more structured approach.

Chardonnay — style-dependent oxidation management
Chenin Blanc — high acidity aids SO₂ efficacy
Viognier — highly oxidation-prone
Grüner Veltliner — requires reductive handling
Sauvignon Blanc — aromatic preservation critical

References

Singleton, V.L. (1987). “Oxygen with Phenols and Related Reactions in Musts, Wines, and Model Systems: Observations and Practical Implications.” American Journal of Enology and Viticulture, 38(1), 69-77. AJEV Link
Waterhouse, A.L., & Laurie, V.F. (2006). “Oxidation of Wine Phenolics: A Critical Evaluation and Hypotheses.” American Journal of Enology and Viticulture, 57(3), 306-313. DOI: 10.5344/ajev.2006.57.3.306
Oliveira, C.M., Ferreira, A.C.S., De Freitas, V., & Silva, A.M. (2011). “Oxidation Mechanisms Occurring in Wines.” Food Research International, 44, 1115-1126. DOI: 10.1016/j.foodres.2011.03.050
Kritzinger, E.C., Bauer, F.F., & du Toit, W.J. (2013). “Role of Glutathione in Winemaking: A Review.” Journal of Agricultural and Food Chemistry, 61, 269-277. DOI: 10.1021/jf303665z
AWRI (2024). “Oxidation in White Wines.” Australian Wine Research Institute. https://www.awri.com.au
UC Davis (2024). “Wine Oxidation: Causes and Prevention.” Department of Viticulture and Enology. https://wineserver.ucdavis.edu