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Welcome to Wine Flavor 101B:
Recognizing Defects During Aging
January 14, 2011
Overview of Potential Problems During Aging
Linda F. BissonDepartment 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