Oxygen Treatments Pre- and During Fermentation

1
Oxygen Treatments Pre- and During Fermentation

• Linda F. Bisson
• Department of Viticulture and Enology
• University of California, Davis

2
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

3
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

4
Unintended Goals of Aeration

• Stimulation of spoilage organisms
• Loss of aromatic characters
• Creation of off-characters due to oxidation
  reactions

5
Mixing

• Avoid stratification
• Enhance extraction
• Remove inhibitory Carbon Dioxide
• Provide oxygen for metabolism

6
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

7
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

8
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

9
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

10
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

11
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

12
Color Maturation

• Formation of stable pigments
• Browning reactions

13
Tannin/Mouth Feel Maturation

• Anita to cover

14
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

15
Loss of Aroma Characters

• Loss due to volatility
• Loss due to chemical reactivity
• Loss due to microbial activity
• Loss due to enzymatic activity

16
Creation of Off-Characters

• Aldehydes from chemical reactions
• Off-colors from oxidative reactions
• Stimulation of oxidative organisms

17
Timing of Aeration

• Pre-fermentation
• During fermentation
• Post-fermentation ML
• Post-fermentation aging

18
Pre-Fermentation Aeration

• Fates of oxygen in Juice
• Microbial consumption
• Enzymatic consumption
• Chemical consumption

19
Fates of Oxygen During Fermentation

• Microbial consumption
• Ethanol inhibition of PPO, not of laccase

20
Aeration Winery Trials

• Impact of aeration during pumpover in Grenache
• Impact of oxygen treatments in commercial
  Chardonnay

21
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

22
Confounding Variables

• Impact of oxygen versus simple mixing (thus the
  Nitrogen control)
• Impact of microbes stimulated in control and
  aeration treatments (secondary effects)

23
Grenache Juice Analysis
Initial Must Analysis Initial Must Analysis

Brix 22.2
pH 3.4
TA 5.08 g/L
24
(No Transcript)
25
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

26
Commercial Chardonnay Trial

• Five Treatments
• Control
• Nitrogen-sparged juice
• Aeration pre-inoculation
• Aeration at 18-20 Brix
• Aeration of wine as control

27
Fermentation Curves
28
Fermentation Curves
29
Conclusions

• Yeast strains showed differences
• No differences noted by treatment of fermentation
• Wines available on side table

30
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