Transcript VEN124 Section III - University of California, Davis

Lecture 11:
Stuck Fermentations:
Diagnosis and Rectification
In this lecture we will learn how to
recognize an arrested
fermentation, how to diagnose the
cause of the problem and how to
re-initiate fermentation
Normal Fermentation Profile
Glucose is consumed faster than
fructose
Arrested fermentations will be
high in fructose relative to
glucose
Sugar Consumption
300
Sugar (g/L)
250
Glucose
Fructose
Total Sugar
200
150
100
50
0
0
20
40
60
80
100
120
140
Fermentation Time (hours)
160
180
200
Problem Fermentation Profiles
Types of Problem Fermentations
30
Normal
Long Lag
25
Becoming Sluggish
Sluggish Throughout
Brix
20
Abrupt Arrest
15
10
5
0
0
50
100
150
200
-5
Time (hours)
250
300
350
Types of Sluggish Fermentations
• Long Lag
Types of Problem Fermentations
30
Normal
Long Lag
25
Becoming Sluggish
Sluggish Throughout
Brix
20
Abrupt Arrest
15
10
5
0
0
50
100
150
200
-5
Time (hours)
250
300
350
Causes of Long Lag
• Poor health of starter culture
• Presence of inhibitors
• Poor grape quality
– Mold infestation
– Premature initiation of fermentation
Poor Health of Starter Culture
• Active Dry Yeast:
Past expiration date
Not hydrated properly
Not stored properly
• Natural Fermentation: Yeast numbers
low
Inhibitory microbes
present
Poor yeast strain
present
Presence of Inhibitors
•
•
•
•
Sulfur dioxide concentration too high
Sulfur dioxide added improperly
Microbial activity resulting in inhibition
Pesticide/fungicide residues on grapes
at harvest
• Temperature of must/juice too high/low
Poor Grape Quality
• Infected grapes: loss of micronutrients
• Infected grapes: high microbial loads
• Loss of free oxygen
Types of Sluggish Fermentations
• Long Lag
• Slow Rate Over Entire Course of
Fermentation
Types of Problem Fermentations
30
Normal
Long Lag
25
Becoming Sluggish
Sluggish Throughout
Brix
20
Abrupt Arrest
15
10
5
0
0
50
100
150
200
-5
Time (hours)
250
300
350
Causes of Slow Rate Over Entire
Time Course
•
•
•
•
Failure to reach maximum cell density
Nutrient (growth factor) limitation
Strain a poor choice for conditions
Inhibitory fermentation conditions:
temperature, pH, ionic
imbalances
Types of Sluggish Fermentations
• Long Lag
• Slow Rate Over Entire Course of
Fermentation
• Rapid Rate Becoming Slow
Types of Problem Fermentations
30
Normal
Long Lag
25
Becoming Sluggish
Sluggish Throughout
Brix
20
Abrupt Arrest
15
10
5
0
0
50
100
150
200
-5
Time (hours)
250
300
350
Causes of a Decrease in Rate
•
•
•
•
•
Poor ethanol tolerance
Loss of viability
Loss of fermentative capacity
Nutrient (survival factor) limitation
Poor strain
Types of Sluggish Fermentations
• Long Lag
• Slow Rate Over Entire Course of
Fermentation
• Rapid Rate Becoming Slow
• Abrupt Stop
Types of Problem Fermentations
30
Normal
Long Lag
25
Becoming Sluggish
Sluggish Throughout
Brix
20
Abrupt Arrest
15
10
5
0
0
50
100
150
200
-5
Time (hours)
250
300
350
Causes of an Abrupt Stop
• Temperature shock
• Rapid build up of inhibitors:
acetic/organic acids
• pH decreases too much
• Strain very ethanol sensitive
Most Common Causes of
Stuck/Sluggish Fermentations
•
•
•
•
•
•
Nutrient deficiency
Temperature extreme
Presence of a toxic substance
Microbial incompatibility
Deficient yeast strain
Poor fermentation management
decisions
Why are stuck fermentations difficult
to treat?
• Cells adapt to adverse conditions by reducing
fermentation capacity
• Biological adaptation difficult to reverse
• Diagnosis of cause of fermentation problem
difficult
• Conditions that cause stuck fermentations are
also conducive to cell death
• New inocula respond to cell death by
arresting activities
Fermentation Variables Impacting
Progression and Rate
• Oxygenation
Oxygenation
• Oxygen is a micronutrient electron
acceptor
• Oxygen is a survival factor
• Oxygen can lead to color changes
(brown, pink, orange)
Fermentation Variables Impacting
Progression and Rate
• Oxygenation
• Mixing: natural or assisted
Mixing
• Separates yeast from end products
• Brings yeast in contact with new
nutrients
• Can facilitate skin extraction in reds and
solids extraction in whites and reds
Fermentation Variables Impacting
Progression and Rate
• Oxygenation
• Mixing: natural or assisted
• Type of Fermentation Vessel
Fermentation Vessel
•
•
•
•
Stainless steel can be cooled
Stainless steel easier to sanitize
Stainless steel is inert
Wood: Can impart positive flavors and
aromas
• Wood: Difficult to clean; impossible to
sterilize
• Wood: Develops stable biofilm of microflora
Fermentation Variables Impacting
Progression and Rate
•
•
•
•
Oxygenation
Mixing: natural or assisted
Type of Fermentation Vessel
Inoculation Practices
Inoculation Practices
• Spontaneous Fermentation
• Inoculated Fermentation
Fermentation Variables Impacting
Progression and Rate
•
•
•
•
•
Oxygenation
Mixing: natural or assisted
Type of Fermentation Vessel
Inoculation Practices
Temperature of fermentation
Temperature
• Affects presence and persistence of
wild flora
• Affects fermentation and growth rates
• Extremes are inhibitory
• Impacts spontaneous chemical
reactions
Fermentation Variables Impacting
Progression and Rate
•
•
•
•
•
•
Oxygenation
Mixing: natural or assisted
Type of Fermentation Vessel
Inoculation Practices
Temperature of fermentation
Supplementation/Juice treatments
Supplementation
• Prevents nutritional deficiency
• May impact spectrum of yeast end
products
• Residual nutrients encourage growth of
spoilage organisms
• Unwanted byproducts may be made
Juice/Must Supplements
• Diammonium phosphate (0.96 g/L;
8 lbs/1000 gal)
• Yeast nutritional supplements (varies by
producer)
• Yeast autolysates (3lb/1000 gal)
• Thiamin hydrochloride (0.005 lb/1000
gal)
Other Juice Treatments
•
•
•
•
Fining
Centrifugation
Aeration
Clarification: settling/filtration
Fermentation Variables Impacting
Progression and Rate
•
•
•
•
•
•
•
Oxygenation
Mixing: natural or assisted
Type of Fermentation Vessel
Inoculation Practices
Temperature of fermentation
Supplementation/Juice treatments
Lees contact
Grape Lees Contact
• Extraction of nutrients
• Extraction of grape characters
• Function as solids
Fermentation Variables Impacting
Progression and Rate
•
•
•
•
•
•
•
•
Oxygenation
Mixing: natural or assisted
Type of Fermentation Vessel
Inoculation Practices
Temperature of fermentation
Supplementation/Juice treatments
Lees contact
Presence of solids
Presence of Solids
• Natural (grape material) or added
(bentonite, yeast hulls)
• Stimulate fermentation
• Stimulate growth
• Source of nutrients
• Removal of inhibitory components
Re-initiation of Stuck Fermentations
• Correct diagnosis of nature of the
problem important
• If re-inoculating, make sure inoculum is
adapted to conditions of stuck wine
• Serial re-inoculation
• May need to remove existing biomass
Serial Re-Inoculation
Arrested Wine
Fresh
Juice
Serial Re-Inoculation
Transfer initial 50:50 blend to second tank
when it is 2-4 Brix above the arrested
Brix level of the stuck fermentation
Do not let any of the intermediate steps in
the series go dry, transfer them at the
equivalent or slightly higher Brix than
the arrested wine
This concludes the
section on the alcoholic
fermentation.