Transcript The Impact of Yeast on Wine Aroma and Flavor: The Good, the Bad

Sulfur Compounds in Wine
Linda Bisson
Department of Viticulture and
Enology
Introduction to S-Containing Faults
Why Are Sulfur Compounds a
Problem?
Low thresholds of detection
Negatively-associated aromas
Chemical reactivity
Difficulty in removal
Difficulty in masking
The Classic Sulfur Fault Descriptors
 Rotten egg
 Fecal
 Rubber/Plastic tubing
 Burnt match
 Burnt molasses
 Burnt rubber
 Rotten vegetable: cauliflower, cabbage, potato,
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asparagus, corn
 Onion/Garlic
 Clam/Tide pool
 Butane/Fuel/Chemical
The Sulfur Taints
Hydrogen sulfide
 Higher sulfides
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Mercaptans
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Methyl (Ethyl) mercaptan
Thioesters
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Dimethyl (Diethyl) sulfide
Dimethyl disulfide
Methyl (ethyl) thioacetate
Other S-amino acid metabolites
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Thioethers
Cyclic and heterocyclic compounds
Sources of Sulfur Compounds
Non-biological
• Elemental sulfur
• S-containing pesticides
Biological
• Sulfate/Sulfite reduction and reduced sulfide
reactions
• S-containing amino acid metabolism
• S-containing vitamins and cofactors degradation
• Glutathione metabolism and degradation
• S-containing pesticides degradation
• Elemental sulfur
Timing of Sulfur Fault Formation
Primary Fermentation Early: Hydrogen
Sulfide
 Primary Fermentation Late: Hydrogen
Sulfide
 Post Fermentation: Hydrogen Sulfide or
Sur Lie Faults
 Bottling: S-fault development
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Hypotheses to Explain S-Taint
Formation
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Correlated with H2S formation during the primary
fermentation
Correlated with late H2S formation (peak 2) but not with
H2S formation during primary fermentation
Associated with S-containing amino acid levels during
primary fermentation
Due to degradation of S-containing metabolites during
yeast lees aging, but not related to levels of these
compounds present in the initial juice
Yeast strain most important
Juice composition most important
Problems with Previous Studies
Lack of control of all variables
 Invalid comparisons (too many variables)
 Confounding factors not considered to be
important
 Differences in strains and conditions used
 Driving reactions by having an excess of
precursors, beyond anything found in
juices or wines
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HYDROGEN SULFIDE
Why is H2S formed?
Off-shoot of metabolism
 Reductive environment
 Signaling molecule
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Hydrogen Sulfide Formation: OffShoot of Metabolism
 Due to release of reduced sulfide from the enzyme
complex sulfite reductase
 Reduction of sulfate decoupled from amino acid
synthesis
 Sulfate reduction regulated by nitrogen availability
 Lack of nitrogenous reduced sulfur acceptors leads
to excessive production of reduced sulfate and
release as H2S
 Also a stress response
 Strain variation
Stress Response: Reduction
Pathway Remains Operational
Need cysteine for glutathione (tripeptide
cytoplasmic redox (electron) buffer
 Need methionine for Sadenosylmethionine and one carbon
transfers needed for ethanol tolerance
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Sulfate Reduction Pathway
SO4
SUL1, SUL2
SO4
MET3
Adenylylsulfate
H2 S
MET14
Phosphoadenylylsulfate
Sulfite
Sulfide
Cysteine
CYS3
Cystathionine
CYS4
MET16 (1,8,20,22)
MET10 (1,5?,8,20)
MET17/25/15
Homocysteine
MET6
Methionine
Hydrogen Sulfide Formation:
Reductive Environment
Biological energy is obtained from recapture
of light (carbon bond) energy, from proton
movements and from electron movements
 Cell is dealing with an excess of electrons
that exceeds buffering capacity
 Many electrons can be used to reduce a
single sulfate molecule restoring the proper
balance of cytoplasmic electrons
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Hydrogen Sulfide Formation:
Reductive Environment
Tank dimensions leading to stratification of
electron gradients
 Settling of yeast cells
 Chemical composition of juice
 Oxygen level and content of juice
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Hydrogen Sulfide Formation:
Signaling Molecule
Hydrogen sulfide coordinates population
metabolic activities: shuts down respiration
in favor of fermentation, coordinating
population of cells in fermentation
 Hydrogen sulfide inhibits respiration of a
variety of organisms: allows more rapid
domination of fermentation
 Explains selective pressure for high sulfide
producers in the wild
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Current Understanding of H2S Formation
Nitrogen levels not well-correlated with H2S
formation, but generally see increased H2S
at lower nitrogen
 Tremendous strain variation in H2S
production
 Can get H2S with high nitrogen
 Get more H2S with higher solids content
 Get more H2S with unsound fruit
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Factors Impacting H2S Formation
Level of total nitrogen
 Level of methionine relative to total nitrogen
 Fermentation rate
 Use of SO2
 Vitamin deficiency
 Presence of metal ions
 Inorganic sulfur in vineyard
 Use of pesticides/fungicides
 Strain genetic background
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Timing of Formation of H2S
Brix
H2S
Time
Timing of Formation of H2S
•Early (first 2-4 days): due to N/vitamin
shortage, electron imbalance, signaling
•Late (end of fermentation): due to
degradation of S-containing compounds
•Sur lie (post-fermentation aging): due to
autolysis
•In Bottle: screw cap closures: return
from an altered chemical form
HIGHER SULFIDES
Higher Sulfides
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Emerge late in fermentation and during sur lie
aging
Release of compounds during entry into
stationary phase by metabolically active yeast
Come from degradation of sulfur containing
amino acids
Biological
Chemical
From reaction of reduced sulfur intermediates with other
cellular metabolites?
Formed chemically due to reduced conditions?
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Degradation of cellular components: autolysis
Volatile Sulfur Compounds
Methanethiol: CH3-SH
 Ethanethiol: C2H5-SH
 Dimethyl sulfide: CH3-S-CH3
 Dimethyl disulfide: CH3-S-S-CH3
 Dimethyl trisulfide: CH3-S-S-S-CH3
 Diethyl sulfide: C2H5-S-C2H5
 Diethyl disulfide: C2H5-S-S-C2H5
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Sources of Higher Sulfides
S-Containing Amino Acids
 S-Containing Vitamins and Co-factors
 Glutathione (Cysteine-containing tripeptide
involved in redox buffering)
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Defining Metabolic Behaviors Resulting
in Taint Formation
S-amino acid catabolism
 Vitamin/Co-factor interactions and
metabolism
 Glutathione turnover and reactions
 Metabolic roles of sulfate reduction
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Defining Metabolic Behaviors Resulting
in Taint Formation
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S-amino acid catabolism
Degradation of methionine and cysteine: methional
and methionol
 Chemical reaction products of methionine and
cysteine: stress resistance
 Influence of wine composition and chemistry on
yeast behavior
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Vitamin/Co-factor interactions and metabolism
 Glutathione turnover and reactions
 Metabolic roles of sulfate reduction
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Defining Metabolic Behaviors Resulting in
Taint Formation
S-amino acid catabolism
 Vitamin/Co-factor interactions and
metabolism
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 Role
of thiamin
 Role of S-adenosylmethionine
Glutathione turnover and reactions
 Metabolic roles of sulfate reduction
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Defining Metabolic Behaviors Resulting in
Taint Formation
S-amino acid catabolism
 Vitamin/Co-factor interactions and
metabolism
 Glutathione turnover and reactions
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 Role
in stress response: prevention of
oxidative damage
 Impact of nitrogen level on metabolism
 Biological turnover of ‘reacted’ glutathione
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Metabolic roles of sulfate reduction
Defining Metabolic Behaviors Resulting in
Taint Formation
S-amino acid catabolism
 Vitamin/Co-factor interactions and
metabolism
 Glutathione turnover and reactions
 Metabolic roles of sulfate reduction
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Stress response:
Prevention of oxidative damage
 Role in ethanol tolerance
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Environmental/metabolic detoxification
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Banking on reactivity to inactivate a toxic substance
Metabolic demands
Understanding the Interface between Metabolite
Production and Wine Chemistry and Composition
What environmental conditions impact Scompound metabolic activities?
 Separating a biological response from a
chemical one
 Control the metabolites
 Control the chemistry
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Sulfur Compound Flight #1
Spiked Compounds
Glass 1: Control Wine (Cabernet Sauvignon)
Glass 2: Hydrogen sulfide H2S
Glass 3: Dimethyl sulfide CH3-S-CH3
Glass 4: Dimethyl trisulfide: CH3-S-S-CH3
Glass 5: Diethyl sulfide: C2H5-S-C2H5
Glass 6: Diethyl disulfide: C2H5-S-S-C2H5
Sulfur Compound Flight #1
Spiked Compounds
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G 1: Control Wine (Cabernet Sauvignon)
G2: Hydrogen sulfide: rotten egg
G 3: Dimethyl sulfide: cabbage, cooked corn,
asparagus, canned
vegetable
G 4: Dimethyl trisulfide: meaty, fishy, clams, green,
onion, garlic, cabbage
G 5: Diethyl sulfide:
garlic, onion
G 6: Diethyl disulfide: overripe onion, greasy,
garlic, burnt rubber,
manure
Sulfur Compound Flight #2:
Taints produced late in fermentation
Glass 1: Control Wine (Cabernet Sauvignon)
Glass 2: Ethanethiol
Glass 3: Mercapto -2- methyl propanol
(Methionol)
Glass 4: Methyl thiopropionaldehyde
(Methional)
Glass 5: Mercapto-3-methyl butanol
Glass 6: BM45 French Colombard
Sulfur Compound Flight #2
Spiked Compounds
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G 1: Control Wine (Cabernet Sauvignon)
G 2: Ethanethiol: onion, rubber, natural gas
G 3: Methionol: cauliflower, cabbage, potato
G 4: Methional: musty, potato, onion, meaty
G 5: Mercapto-3-methyl butanol: meaty
G 6: French Colombard: reduced
BM 45:
Isolated in Montalcino
 Produces high polyphenol reactive
polysaccharides = mouth feel
 Has high nitrogen requirements and can
produce H2S
 Aroma characteristics: fruit jam, rose,
cherry, spice, anise, cedar and earthy
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