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Introduction to
Oxidation in Wine
Andrew L. Waterhouse
Department of Viticulture & Enology
University of California, Davis
Oxidation Avoidance
Traditional limit to wine preservation
 Current technology can exclude oxygen
 Wine oxidation - a fault?

Manage Wine Oxidation

At crush / press
– Anaerobic press to hyperoxidation

Fermentation
– Add oxygen for yeast, reductive aromas

Post fermentation/s
– Micro-ox, barrels, racking

In bottle
– Affects flavor development
Oxygen Measurement

Standard meter
– Limit of Detection ~0.5 ppm

Orbisphere or other Clark electrode
– LOD ~2 ppb

Nomasense, Mocon, others
– Oxydots, fiber optic measure-contact not
needed! 10 ppb
– Temperature sensitive!
Antioxidants
SO2
 Ascorbic acid
 Glutathione

Wine Oxidation Chemistry
O
OH
O2 +
EtOH
O
OH
Acetaldehyde
+ H2O2
Step 1
Step 2
Oxygen reacts with phenols to yield
quinone and hydrogen peroxide
 Hydrogen peroxide oxidizes ethanol to
acetaldehyde

Known Oxidation Products

Quinones
– Thiol adducts
– Coupling Products

Aldehydes
– Acetaldehyde
– Glyoxylic Acid
• (Tartaric Acid product)
– Flavonoid coupling
OH
O
O
Oxidative Changes in Wine

Formation of quinones from catechols
– React with thiols, SO2, ascorbate,
phenolics

Fenton oxidation of alcohols
– Formation of aldehydes
– Reactions of all other substances
Oxygen Pathway in Wine
RC=O
O2
RC=O
Fe+3
Fe+2
RCOH
5
1
(Hydroperoxyl
radical)
O2
+
H
Fe+3
RCHOH
(Hydroxyl radical)
Fe+3
4
2
Fe+2
(Semiquinone radical)
3
(Quinone)
(Hydrogen peroxide)
Sulfur Dioxide and Oxygen

Sulfite is the sink for oxidation
O2 + 2 SO2
2 SO3
 1 mg of O2 will consume 4 mg SO2


SO3 + H2O
H2SO4
Polyphenols are Pro-oxidants

Generation of quinone and hydrogen
peroxide from dioxygen
OH
Fe+2
HO O
O2
H+
O
O
+
HO OH
+
OH
Catechin + 3-Mercaptohexanol
OH
O
OH
O
HO
HO
O
OH
OH
+
O
S
SH
OH
HO
OH
Nikolantonaki , ACA 660: 102 (10)
 Blanchard, AJEV 55:115 (04)

OH
Catechin dimer in model juice

Poupard, J Chrom A, 1179: 161 (08)
Quinone Options
OH
OH
?
OH
Ascorbate
OH
O
OH
HO
OH
Phloroglucinol
O
RSH
OH
S R
OH
(Quinone)
AA's, Strecker
Degradation
Phenolic Coupling
(polymerization)
SO2
OH
Aldehydes ?
OH
Mercaptan Trapping
Oxygen Pathway in Wine
RC=O
O2
RC=O
Fe+3
Fe+2
RCOH
5
1
(Hydroperoxyl
radical)
O2
+
H
Fe+3
RCHOH
(Hydroxyl radical)
Fe+3
4
2
Fe+2
(Semiquinone radical)
3
(Quinone)
(Hydrogen peroxide)
Peroxide Competition
Fe+3
H2O2
Fe+2
SO2
H2O
·OH
EtOH
CH3CHO
Wine Minor Components
Red Wine Composition, Minor Components
Acetaldehyde
Volatile Acidity
Glycerol
Sugar
Higher Alcohols
Sorbitol & Mannitol
Phenols
Sulfites
Minerals *
Esters
Amino acids
Acid
Oxidation of Wine Acids
(Alcohols) to Carbonyls

Pyruvic
– Observed in wine
– Reacts with
anthocyanins to
make wine
pigments

Glyoxylic
– Observed in wine
– Condenses with
flavan-3-ols
O
OH
O
H2O2
HO
O
Fe+2
CH3
CH3
Lactic Acid
(or Malic)
O
H2O2
HO
OH
O
Pyruvic Acid
O
OH
OH
Fe+2
OH
O
HO
O
OH
O
OH
CH
OH
Tartaric Acid
Hydroxymalonic
Glyoxylic Acid
Aldehyde Pigment Reactions

“D-ring” formation by acetaldehyde and
pyruvate
R1
O
R1
OH
OH
H
HO
O
R2
OH
+
HO
+
O
Glu
O
R2
O
or
OH
O
Glu
O
O
R
R = H,
O
OH
Alcohol Oxidations with ∙OH

Aldehydes known oxidation products
Wine Oxidation
Aroma and color changes
 Can be managed

– A few key steps need better understanding
Many current investigations
 State of the art and practice today
