Oxygen Treatments
Pre- and During
Fermentation
Linda F. Bisson
Department of Viticulture and Enology
University of California, Davis
Oxygen During Juice Fermentation
• Low level exposure in juice during
pressing operation
• Hyperoxygenation to get rid of
browning potential
• Deliberate addition to fermentation
to stimulate yeast
Intended Goals of Aeration
• Mixing
• Providing oxygen as nutrient for yeast
or ML bacteria
• Stimulation of non-Saccharomyces
organisms
• Aroma maturation
• Color maturation
• Tannin/mouth feel maturation
Unintended Goals of Aeration
• Stimulation of spoilage organisms
• Loss of aromatic characters
• Creation of off-characters due to
oxidation reactions
Mixing
• Avoid stratification
• Enhance extraction
• Remove inhibitory Carbon Dioxide
• Provide oxygen for metabolism
Mixing
• Avoid stratification
• Distribute Ethanol Levels
• Mix Yeast
• Bring in new nutrients
• Distribute inhibitory non-volatile end
products
• Enhance extraction
• Remove inhibitory Carbon Dioxide
• Provide oxygen for metabolism
Providing Oxygen as a Nutrient
• Oxygen enables adaptation
• Allows aerobic organisms to make
energy for adaptation of cell to juice
conditions
• Oxygen is a survival factor
• Allows formation of desired
lipid/phospholipid composition
• Enables formation of sterols
• Maintains cytoplasmic redox status
• Catalyst in biochemical reactions
Timing of Oxygen Addition
• Grape surface microbes tend to be
aerobes and will deplete oxygen
• Organisms need oxygen to survive
• Organisms need oxygen to metabolize
• Grape and mold oxidases will consume
molecular oxygen as substrate
• Phenolic compounds in juice will react
with oxygen
Timing of Oxygen Addition
• To benefit yeast:
• Need to add oxygen once fermentative
yeast populations are established
• Use of sulfite to inhibit enzymatic
consumption of molecular oxygen
• Use of heat treatments to inhibit
enzymatic consumption of molecular
oxygen
Stimulation of nonSaccharomyces Organisms
• Acetic Acid bacteria on fruit
• Lactic Acid bacteria on fruit
• Non-Saccharomyces yeasts
• Aerobes on surfaces of winery
equipment
• Enables transition to fermentative
modes of metabolism
• Generation of complexity
Aroma Maturation
• Manipulation of juice chemistry
• Challenging because of multiple
possible fates of added O2
• Redox reactions difficult to predict
and control
• Loss of volatile aromas
Color Maturation
• Formation of stable pigments
• Browning reactions
Tannin/Mouth Feel Maturation
• Anita to cover
Stimulation of Spoilage Organisms
• Oxygen is essential to most organisms
• Needed for oxidative metabolism or
respiration
• Needed as electron acceptor in many
reactions
• Chemical catalyst
• Can enable survival not just growth
Loss of Aroma Characters
• Loss due to volatility
• Loss due to chemical reactivity
• Loss due to microbial activity
• Loss due to enzymatic activity
Creation of Off-Characters
• Aldehydes from chemical reactions
• Off-colors from oxidative reactions
• Stimulation of oxidative organisms
Timing of Aeration
• Pre-fermentation
• During fermentation
• Post-fermentation: ML
• Post-fermentation: aging
Pre-Fermentation Aeration
• Fates of oxygen in Juice:
Microbial consumption
Enzymatic consumption
Chemical consumption
Fates of Oxygen During Fermentation
• Microbial consumption
• Ethanol inhibition of PPO, not of
laccase
Aeration Winery Trials
• Impact of aeration during pumpover
in Grenache
• Impact of oxygen treatments in
commercial Chardonnay
The Grenache Trial
• Pumpovers were twice daily with sufficient
time to pump over one tank volume
• Three treatments
• Normal Pumpover with no added air
• Pump with constant aeration via insertion
of air into stream
• Insertion of nitrogen instead of air in to
the stream
• Used different closures on the three
treatments
Confounding Variables
• Impact of oxygen versus simple
mixing (thus the Nitrogen control)
• Impact of microbes stimulated in
control and aeration treatments
(secondary effects)
Grenache Juice Analysis
Initial Must Analysis
Brix
pH
TA
22.2⁰
3.4
5.08 g/L
Impact of Aeration During Pumpover in Grenache
25
20
Brix
15
Control - No Sparge
10
Air Sparge
Nitrogen Sparge
5
0
1
-5
2
3
4
5
6
7
Time (Day)
8
9
10
11
12
Findings
• All fermentations completed
• Nitrogen-sparged sample fermented
slightly faster
• Air-sparged sample showed a lag
consistent with growth of other
organisms
• Air-sparged sped up as ethanol
increased, consistent with oxygen as
survival factor
Commercial Chardonnay Trial
• Five Treatments:
• Control
• Nitrogen-sparged juice
• Aeration pre-inoculation
• Aeration at 18-20 Brix
• Aeration of wine as control
Fermentation Curves
Fermentation Curves
Conclusions
• Yeast strains showed differences
• No differences noted by treatment of
fermentation
• Wines available on side table
Grenache Tasting
• Glass 1: Control, no sparge
• Glass 2: Air sparge
• Glass 3: Nitrogen sparge
• Glass 4: Cork closure
• Glass 5: Synthetic Closure
• Glass 6: Synthetic Closure