Welcome to Wine Flavor 101B: Recognizing Defects During Aging January 14, 2011

Overview of Potential Problems During Aging Linda F. Bisson Department of Viticulture and Enology University of California, Davis, CA

Off-Characters Found in Wine  Can originate in vineyard  Can derive from microbial activity  Can arise from conditions of aging

Defects Arising During Aging  Microbial activity  Chemical reactions  Contaminant transfer

MICROBIAL ACTIVITY

Microbial Off-Characters During Aging  Lactic acid bacteria  Acetic acid bacteria  Spoilage yeasts –Film formers –Residual sugar utilizers –Survivalists

Microbial Off-Characters During Aging  Off-odors, off-tastes, off-colors, hazes, films, precipitates and sediments  Direct synthesis  Loss of aroma characters: microbial suppression or buffering  Microbial modification of grape characters  Microbial end products as reactants

Microbial Off-Odors  S-compounds  Aldehydes  Vinyl phenols  Amino acid derivatives  Grape compound metabolites

Microbial Off-Tastes  Sourness  Bitterness  Slimy (okra) finish

Microbial Off-Colors  Pink  Orange

Hazes, Films, Precipitates and Sediments  Result of microbial biomass/biofilm  Production of polysaccharides  Production/modification of tannin-interacting components  Visual or gritty

CHEMICAL REACTIONS

Chemical Off-Characters During Aging  Unmasking vineyard defect  Dependent upon microbial end products  Oxidation-reduction driven

Unmasking Vineyard Defect  Loss of aromatic esters  Degradation of grape glycosides and loss of volatiles and aging potential

Off- Characters Dependent Upon Microbial End Products  Masking due to aldehyde/higher alcohol formation  Production of chemically reactive components: diacetyl  Production or modification of redox reactants or redox potential

Oxidation-Reduction Condition  Redox reactions refer to transfer of electrons  Chemical reactions can both consume or release electrons  The impact of oxygen in wine is due to chemical reactivity and the tendency to pick up electrons

CONTAMINANT TRANSFER

Contaminant Transfer  From corks  From oak  From winery flora

Contaminant Transfer from Corks AWRI:  Trichloroanisole (TCA; cork taint)  2-Methoxy 3,5-dimethylpyrazine (MDMP)  Host of other off-characters can be derived from cork

Contaminant Transfer from Oak Chatonnet:  TCA  2-Methoxy 3,5-dimethylpyrazine (MDMP)  Host of other compounds depending upon how barrel is made and oak is treated

From Winery Flora  TCA  MDMP  Geosmin  Compounds made by winery flora (molds and bacteria) can be absorbed into the wine

Today’s Program  Chemical Issues During Aging  Spoilage by Acetic Acid Bacteria  Yeast Spoilage  Emphasis: Brettanomyces