Transcript Assessments of Microbial Activity in Wine

Assessments of Microbial Activity
in Wine
Linda F. Bisson
Department of Viticulture and Enology,
UCD
December 13, 2013
Post-Fermentation Microbial Activity
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Turbidity
CO2 Production
Film Production
Polysaccharide Production
Positive Character Production
Negative Character Production
– Odor
– Taste
– Color
– Sediment
– Haze
Mechanisms to Assess PostFermentation Microbial Presence
• Microscopically
• Appearance of Wine
– Turbidity
– Effervescence
– Films
• Analysis of Metabolic Activity
The Types of Impacts of Microbial
Metabolites
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Positive character synthesis
Negative character synthesis
Modify existing character
Enhance or amplify perception of existing characters
Diminish or buffer perception of existing characters
Matrix effects: change in chemical properties
Positive Contributions to Aroma
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Direct synthesis
Release of bound molecules
Autolysis factors
Indirect (chemical) effects
Matrix effects
Types of Microbial Transformations of
Flavor 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
Microbial Components Impacting
Wine Flavor
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Metabolites
Enzymes
Catalysts
Mannoproteins and Polysaccharides
Direct Synthesis
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Esters
Alcohols
Aldehydes
S-volatiles
Acids
Release of Bound Molecules
• Thiols in Sauvignon blanc
– Cysteine conjugates
– Carbon sulfur lyase activity
• Terpenes
– Β-Glucosidase activity
• Norisoprenoids
– Β-Glucosidase activity
Autolysis Factors
• Release of active enzymes: hydrolases
• Release of cellular macromolecular
components
• Breakdown of cellular macromolecular
components
Indirect (Chemical) Effects
• Creation of reactive molecules
– S-containing compounds
– Diacetyl
– Aldehydes
• Alteration of pH
• Alteration of Redox status of juice
Matrix Effects
• Alteration of solution chemistry
• Production of flavor enhancers
– Dimethyl sulfide
• Production of masking factors
– Fusel family
– Hydrogen sulfide
Post-Fermentation Microbiota
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ML Fermentation
Surface films
Brettanomyces spoilage
Yeast spoilage
Monitoring Lactic Acid Bacterial
Activity in Wine
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Measure decrease in malate levels
Assess change in pH
Note presence of effervescence
Follow increase in wine turbidity
Evaluate aroma profile
Monitoring Lactic Acid Bacterial
Activity in Wine
• Measure decrease in malate levels
– Will tell you when it is done
• Assess change in pH
– Something is happening, will not tell you it is complete
• Note presence of effervescence
– Something is producing CO2
• Follow increase in suspended wine turbidity
– Something is growing in the wine
• Evaluate aroma profile
– Characteristic compounds of lactic acid bacteria
• Diacetyl
• Acetic acid
• Off-characters
ML Fermentation
• Monitor disappearance of malate
– Paper chromatography
– Enzymatic
• By hand
• Automated
– Spectroscopy
• UV/VIS
• FTIR (Fourier Transform Infrared)
– Photometric analysis
Note on Measurements
• Some methods are direct
– Interference is minimal
– Misidentification of compound rare
• Some methods are indirect
– Need to make sure peak is correctly being
identified
– Interference can be a problem
– Misidentification can occur if unexpected
components are present
Lactic Acid Bacteria Off-Odors
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Mousiness
“Poo” off- notes
Animal characteristics: fur, meaty
Floral taints: geranium
Metallic
Vomit
Rancidity
Mousiness
Several compounds(oxidation products of
lysine) have been implicated in this offcharacter:
2,4,6-trimethyl-1,3,5-triazine
2-ethyl-3,4,5,6-tetrahydropyridine
2-acetyl-3,4,5,6-tetrahydropyridine
Lactic Acid Bacteria Off-Tastes
• Enhanced sourness
• Bitterness
Monitoring Lactic Acid Bacterial
Activity in Wine: Best Practices
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Microscopic analysis
Aroma analysis
Taste analysis
Monitor malate levels
Surface Films
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Bacteria or Yeast
Most Often Both
Off-Character Production
Film Microbiota Can Produce Copious
Amounts of Off-Characters Due to Availability
of Oxygen
Brettanomyces
• Problem in barrels
• Can monitor 4-ethyl phenol or 4 ethyl guaiacol
formation by nose or analytically
• Some wines suppress odors from these
compounds; the mechanism is not understood
• Monitor via microscopy; sometimes
Saccharomyces looks like Brettanomyces
• Genomic/molecular monitoring of presence
Spoilage Yeasts
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Use residual sugar
Turbidity and effervescence in bottle
Zygosaccharomyces
Saccharomyces
Advice
• Need to know you have the potential for a
problem before the off-character appears
• Some of these off-characters are transient
• Some characters difficult to remove
– Blending out
– Charcoal fining
• Need to be careful to NOT spread it around
the winery