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