Assessments of Microbial Activity in Wine

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Transcript Assessments of Microbial Activity in Wine

Assessments of Microbial Activity
in Wine
Linda F. Bisson
Department of Viticulture and Enology,
December 13, 2013
Post-Fermentation Microbial Activity
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
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
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
– Liberation of grape flavor components from
• Secondary roles
– Provide chemical reactants
– Enzymatic modification of grape/oak flavors
– Impact Redox status and buffering capacity
Microbial Components Impacting
Wine Flavor
Mannoproteins and Polysaccharides
Direct Synthesis
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
• Breakdown of cellular macromolecular
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
ML Fermentation
Surface films
Brettanomyces spoilage
Yeast spoilage
Monitoring Lactic Acid Bacterial
Activity in Wine
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
• 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
– Interference can be a problem
– Misidentification can occur if unexpected
components are present
Lactic Acid Bacteria Off-Odors
“Poo” off- notes
Animal characteristics: fur, meaty
Floral taints: geranium
Several compounds(oxidation products of
lysine) have been implicated in this offcharacter:
Lactic Acid Bacteria Off-Tastes
• Enhanced sourness
• Bitterness
Monitoring Lactic Acid Bacterial
Activity in Wine: Best Practices
Microscopic analysis
Aroma analysis
Taste analysis
Monitor malate levels
Surface Films
Bacteria or Yeast
Most Often Both
Off-Character Production
Film Microbiota Can Produce Copious
Amounts of Off-Characters Due to Availability
of Oxygen
• 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
Use residual sugar
Turbidity and effervescence in bottle
• 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