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

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 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)

Grenache Juice Analysis

Initial Must Analysis

Brix 22.2⁰pH 3.4TA 5.08 g/L

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