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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

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Overview of Problem Fermentations

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  1. Overview of Problem Fermentations Linda F. Bisson Department of Viticulture and Enology Issues in Fermentation Management, 2011

  2. Problem Fermentations • Slow (sluggish) fermentation • Stuck (incomplete, arrested) fermentation • Off-character production • Hydrogen sulfide • Sulfur volatiles • Acetic acid • Undesired Esters

  3. Stuck and Sluggish Fermentations

  4. Stuck and Sluggish Fermentations • Characterized by failure of yeast to consume sugar • Multiple causes • Difficult to treat • Leads to reduced wine quality

  5. Fermentation Profile 5 1 2 Brix 3 4 Time 1: lag time; 2: max fermentation rate; 3: transition point; 4: post-transition fermentation rate; 5: overall time to dryness

  6. 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

  7. Fermentation Capacity Is a Function of: • Yeast Biomass Concentration • Fermentative Ability of Individual Cells

  8. Causes of Stuck/Sluggish Fermentations • Nutrient limitation

  9. 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

  10. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Ionic imbalance

  11. 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

  12. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition

  13. Substrate Inhibition Transporters with a high substrate affinity can get “jammed” at high substrate concentrations G G F F F G

  14. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition • Ethanol toxicity

  15. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition • Ethanol toxicity • Presence of toxic substances

  16. 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

  17. The Most Common Toxins • 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

  18. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition • Ethanol toxicity • Presence of toxic substances • Poor adaptation of strain

  19. 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

  20. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition • Ethanol toxicity • Presence of toxic substances • Poor adaptation of strain • Low pH

  21. 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

  22. Causes of Stuck/Sluggish Fermentations • Nutrient limitation • Nutrient imbalance • Substrate inhibition • Ethanol toxicity • Presence of toxic substances • Poor adaptation of strain • Low pH • Temperature shock

  23. Problem Fermentation Profiles

  24. Types of Sluggish Fermentations • Long Lag

  25. Causes of Long Lag • Poor health of starter culture • Presence of inhibitors • Poor grape quality • Mold infestation • Premature initiation of fermentation

  26. 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

  27. 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

  28. Poor Grape Quality • Infected grapes: loss of micronutrients • Infected grapes: high microbial loads • Loss of free oxygen

  29. Types of Sluggish Fermentations • Long Lag • Slow Rate Over Entire Course of Fermentation

  30. 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

  31. Types of Sluggish Fermentations • Long Lag • Slow Rate Over Entire Course of Fermentation • Rapid Rate Becoming Slow

  32. Causes of a Decrease in Rate • Poor ethanol tolerance • Loss of viability • Loss of fermentative capacity • Nutrient (survival factor) limitation • Poor strain

  33. Types of Sluggish Fermentations • Long Lag • Slow Rate Over Entire Course of Fermentation • Rapid Rate Becoming Slow • Abrupt Stop

  34. Causes of an Abrupt Stop • Temperature shock • Rapid build up of inhibitors: acetic/organic acids • pH decreases too much • Strain very ethanol sensitive

  35. 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

  36. 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

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