Negative Impacts of Oxygen in Wine

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

• 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