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

Alcohols become aldehydes Organic acids become keto acids Reaction with thiols and loss of varietal character Off-Color formationExtensive 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 OrganismsAcetic 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