oxygen treatments pre- and during fermentation linda f. bisson department of viticulture and enology...
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Oxygen Treatments Pre- and During
FermentationLinda F. Bisson
Department of Viticulture and EnologyUniversity 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 non- Saccharomyces 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
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 consumptionEnzymatic consumptionChemical 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)
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
Conclusions
• Yeast strains showed differences•No differences noted by treatment of
fermentation•Wines available on side table