Transcript Yeast Impact on Wine Composition: Overview

Yeast Impact on Wine
Composition: Overview
Linda F. Bisson
Department of Viticulture and Enology
University of California, Davis
Role of Yeast in Wine Composition
Conversion of sugar to ethanol
Production of aromatic compounds
Effects on mouth feel
Modification of plant components
Consumption of nutrients and prevention
of growth of other microorganisms
Creation of reductive environment
impacting a range of subsequent chemical
reactions
Yeast Components Impacting Wine Flavor
Metabolites
Enzymes
Catalysts
Mannoproteins and Polysaccharides
Yeast Production of Aromatic Compounds
Synthesize positive characters
Synthesize negative characters
Modify existing grape characters
Intensify perception of existing characters
Reduce perception of existing characters
Alter wine matrix: change in chemical and
sensory properties
Types of Yeast Impact on Aromatic
Compounds
Primary roles
– Production of flavor compounds de novo from
nutrients
– Liberation of grape flavor components from
precursors
Secondary roles
– Provide chemical reactants
– Enzymatic modification of grape/oak flavors
– Impact Redox status and buffering capacity
Major Classes of Yeast Flavor Compounds
Esters
Sulfur Compounds
Alcohols
Aldehydes
Acids
Carbonyl Compounds
Esters
Ethyl esters of acids
Acetate esters of alcohols
Generated from the reaction of acyl~CoA
with an alcohol
Generally described as generic fruity
characters
Can boost perception of grape varietal
characters
Can mask grape varietal characters
S-Compounds
Derived from sulfate reduction
Derived from catabolism of S-containing
amino acids
Derived from catabolism of glutathione
Derived from degradation of vitamins
Degradation products of grape thiol
precursors: release of varietal character
Alcohols
Ethanol
Amino acid degradation products
Fatty acid-derived alcohols
Role of Alcohols: Buffering of Aroma
Increased solubility of aroma compound
(less volatile)
Creates “ethanol pockets” areas of
enhanced solubility
Affects physical interactions with other
wine components
Decreases perception?
Converted to aldehydes during aging
Aldehydes
Acetaldehyde
Amino acid degradation
Fatty acid derived
Alcohol precursors for oxidation
Acids
Central carbon metabolism
Amino acid degradation
Fatty acid derived
Carbonyl Compounds
Derived from carbon catabolism
Reactive components
Other Compounds
 Sterol metabolism: terpene and terpenelike components
Amino acid derivatives
Take-Home Messages
Roles of yeast in wine aroma and flavor
are varied
Impact depends upon starting juice
composition
Impact depends upon genetic constitution
of the yeast strain
Impact is difficult to predict
Today’s Program
Diversity of Yeast
Discussion of Commercial Yeast Strains
Impact of Nutrient Additions
Nutrient Suppliers Panel
Impact of Solids Level