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

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

Issues With Over-Oxygenation Chemical Enzymatic Microbial

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

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

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

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

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

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

Off-Colors Browning Pinking ‘Going Orange’

Enzymatic Issues Laccase

Microbial Issues Spoilage Organisms Acetic Acid Bacteria Brettanomyces Staphylococcus Flor Yeast

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

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