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 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 O 2 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 22.2⁰ pH 3.4 TA 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 Brix Aeration of wine as control

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