Transcript Overview of Problem Fermentations

Overview of Problem
Fermentations
Linda F. Bisson
Department of Viticulture and Enology
Issues in Fermentation Management,
2011
Problem Fermentations
Slow (sluggish) fermentation
 Stuck (incomplete, arrested) fermentation
 Off-character production

– Hydrogen sulfide
– Sulfur volatiles
– Acetic acid
– Undesired Esters
Stuck and Sluggish
Fermentations
Stuck and Sluggish
Fermentations
Characterized by failure of yeast to
consume sugar
 Multiple causes
 Difficult to treat
 Leads to reduced wine quality

Fermentation Profile
5
1
Brix
2
3
4
Time
1: lag time; 2: max fermentation rate; 3: transition
point; 4: post-transition fermentation rate; 5:
overall time to dryness
Fermentation Profile

Lag time
– Duration?

Maximum fermentation rate
– Rate value?
– Duration?

Transition point
– At what Brix level?
– How sharp?

Post-transition fermentation rate
– Value relative to max fermentation rate?
– Length of time?
– Brix/ethanol/nitrogen level at which it occurs?

Overall time to dryness
Fermentation Capacity Is a
Function of:
Yeast Biomass Concentration
 Fermentative Ability of Individual Cells

Causes of Stuck/Sluggish
Fermentations

Nutrient limitation
Nutrient Limitation

Nitrogen: most often limiting
 Phosphate can also be limiting
 Depending upon circumstances, micronutrient
limitation may also be a problem
–
–
–
–
Pitching yeast
Deficiency in vineyard
Microbial blooms prior to fermentation
Loss during rehydration
Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Ionic imbalance

Ionic Imbalance
Ratio of K+:H+
Must be at least 25:1
Needs to be adjusted early in
fermentation
Probably important in building an ethanol
tolerant membrane
Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Nutrient imbalance
 Substrate inhibition

Substrate Inhibition
Transporters with a high substrate affinity
can get “jammed” at high substrate
concentrations
F
G G
FG
F
Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Nutrient imbalance
 Substrate inhibition
 Ethanol toxicity

Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Nutrient imbalance
 Substrate inhibition
 Ethanol toxicity
 Presence of toxic substances

Presence of Toxic Substances
Toxins may arise from the metabolic
activity of other microbes
 Toxins may arise from metabolic activity of
Saccharomyces
 Toxins may have arisen in vineyard, but
are not inhibitory until ethanol has
accumulated

The Most Common Toxins

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Acetic acid
Higher organic acids (C2 – C4)
Medium chain fatty acids/fatty acid esters
Acetaldehyde
Fungicide/Pesticide residues
Higher alcohols
Higher aldehydes
Killer factors
Sulfur dioxide
Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Nutrient imbalance
 Substrate inhibition
 Ethanol toxicity
 Presence of toxic substances
 Poor adaptation of strain

Poor Adaptation of Strain
Strain may not display ethanol tolerance
 Strain may have high nitrogen/vitamin
requirements
 Strain may be a poor fermentor, but
capable of dominating the fermentation
 Temperature effects

Causes of Stuck/Sluggish
Fermentations
Nutrient limitation
 Nutrient imbalance
 Substrate inhibition
 Ethanol toxicity
 Presence of toxic substances
 Poor adaptation of strain
 Low pH

pH
pH is reduced by metabolism of
Saccharomyces
 Low pH musts (below pH 3.0) may drop to
an inhibitory level (pH 2.7)
 Dependent upon K+ concentration

Causes of Stuck/Sluggish
Fermentations
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Nutrient limitation
Nutrient imbalance
Substrate inhibition
Ethanol toxicity
Presence of toxic substances
Poor adaptation of strain
Low pH
Temperature shock
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:

Natural Fermentation: Yeast numbers
low
Inhibitory microbes
present
Poor yeast strain
present
Past expiration date
Not hydrated properly
Not stored properly
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
Temperature extreme
 Ethanol intolerance
 Nutrient deficiency
 Deficient yeast strain
 Microbial incompatibility
 Presence of an inhibitory substance
 Poor fermentation management decisions

Why are stuck fermentations
difficult to treat?
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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