1. Negative Impacts of Oxygen in Wine
Linda F. Bisson
Department of Viticulture and Enology
University of California, Davis

2. When Is It Over-Oxygenation?
Defects associated with excessive oxygen exposure appear
Dependent upon wine composition

3. Issues With Over-Oxygenation
Chemical
Enzymatic
Microbial

4. Chemical Issues Organic acids become keto acids
Alcohols become aldehydes
Organic acids become keto acids
Reaction with thiols and loss of
varietal character
Off-Color formation
Extensive loss of color and wine becomes sherry-like

5. Aldehydes in Wine Aldehydes
Acetaldehyde from oxidation of Ethanol
Fusel Aldehydes from oxidation of Fusel Alcohols
Benzaldehyde from oxidation of Benzyl Alcohol
Formed chemically from grape/yeast precursors or directly synthesized by microbes
Perception can be enhanced by acetic acid

6. Acetaldehyde Low concentrations: apple, unripe apple
Higher concentrations: oxidized apple, nutty, pungent, chemical
Appearance indicates ethanol is being oxidized and wine should be protected from further oxygen exposure

7. Fusel Aldehydes
Fusel alcohols (oils) are made during amino acid degradation
Fusel alcohols can be reoxidized to aldehydes during aging
Recent experiments suggest fusel aldehydes may be important “impact” compounds in wine

8. Fusel Aldehydes Isobutyraldehyde: banana, acrid, pungent
Isovaleraldehyde: nutty, fruity, cocoa, pungent, acrid
2-Methyl butyraldehyde: aldehydic, berry, cocoa, musty

9. Benzaldehyde Characteristic of oxidized wines
Bitter cherry at low concentrations
Chemical taint at higher concentrations
Can be made microbially

10. Off-Colors
Browning
Pinking
‘Going Orange’

11. Enzymatic Issues
Laccase

12. Microbial Issues Spoilage Organisms Acetic Acid Bacteria Brettanomyces
Staphylococcus
Flor Yeast

13. Staphylococcus pasteuri
Isolated from MOX wine
Normal grape flora resident
Obligate aerobe – sign of beyond excessive oxygen exposure

14. Oxygen Treatments of Wine
Need to know the amount of exposure and its consequences and impact on wine, which will vary by the wine
Monitor for signs of excessive oxygen
If push wine to edge of oxygen consumption, will shorten shelf life