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Lecture 9: Fermentation Management

Lecture 9: Fermentation Management. Reading Assignment: Text, Chapter 4, pages 102-126. This lecture will describe the enological parameters impacting yeast fermentation performance and strategies for management of the fermentation. First Decision: To inoculate or not to inoculate?.

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Lecture 9: Fermentation Management

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  1. Lecture 9: Fermentation Management

  2. Reading Assignment: Text, Chapter 4, pages 102-126

  3. This lecture will describe the enological parameters impacting yeast fermentation performance and strategies for management of the fermentation.

  4. First Decision: To inoculate or not to inoculate?

  5. Sources of Saccharomyces • Vineyard flora • Winery flora • Inoculum

  6. Inoculated Fermentations • With active dry yeast (ADY) • With a starter culture in juice • With an already fermenting must/juice

  7. Level of Inoculum Typically 105 - 106 cells/ml or 1 to 0.1% on a volume/volume basis

  8. Native Flora Fermentations There is no deliberate inoculation with Saccharomyces

  9. Inoculated Fermentations: The Benefits • Predictability • Control of spoilage characteristics • Yeast Neutrality: enhanced varietal characteristics

  10. Inoculated Fermentations: The Negatives • Neutrality: Reduced overall complexity • Fermentation rates too rapid • Wine too “yeasty”

  11. Native Flora Fermentations: The Benefits • Increased microbial complexity • Slower fermentation rates

  12. Native Flora Fermentations: The Negatives • Off-character formation (non-Saccharomyces organisms) • Lack of predictability • Seasonal variation in microbial populations on fruit

  13. Second Decision: Encourage or discourage grape berry microflora?

  14. Grape Berry Microflora • Bacteria • Bacillus • Pseudomonas • Micrococcus • Lactic Acid Bacteria • Acetic Acid Bacteria • Molds • Yeast

  15. Grape Berry Microflora • Bacteria • Molds • Aspergillus • Penicillium • Rhizopus • Mucor • Botrytis • Yeast

  16. Grape Berry Microflora • Bacteria • Molds • Yeast • Kloeckera/Hanseniaspora • Metschnikowia pulcherrima • Hansenula species • Candida species • Saccharomyces

  17. Grape Berry Microflora • 95-98% of total organisms are molds and bacteria • 2-5% are yeast, principally Hanseniaspora and Metschnikowia • Non-Saccharomyces yeasts present at levels of 105 - 106 organisms/mL, Saccharomyces present at 10-2 - 10-3 cells/mL

  18. Factors Affecting Grape Berry Microflora • Rainfall/ Humidity • Insect vectors • Altitude • Temperature • Vineyard fertilization practices • Varietal factors: tightness of cluster • Vineyard practices: inoculation of fruit with soil microbes

  19. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Low pH ( 3.5) inhibits many bacteria • Yeast not pH sensitive at normal juice pH values (2.8-4.2)

  20. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Low temperatures inhibit bacteria • Low temperature enriches for non-Saccharomyces yeasts

  21. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Lack of O2 inhibits all molds • Lack of O2 inhibits aerobic bacteria • Oxygen stimulatory to yeast: not clear how different species are affected

  22. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Nutrient Levels • Must/Juice composition • Supplementation • Timing of addition

  23. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Nutrient Levels • Presence of Inhibitors • Fungicide/pesticide residues • Sulfur dioxide

  24. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Nutrient Levels • Presence of Inhibitors • Microbial Interactions

  25. Types of Microbial Interactions • Production of inhibitors • Acetic acid • Ethanol • Fatty acids • Killer factors • Competition for nutrients • Stimulation • Removal of inhibitor • Release of micronutrients

  26. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Nutrient Levels • Presence of Inhibitors • Microbial Interactions • Inoculation Practices

  27. Inoculation Practices • Early inoculation minimizes impact of wild flora • Higher levels of inoculation limit impact of wild flora

  28. Factors Affecting Persistence of Grape Berry Microflora in Must/Juice • pH • Temperature • Oxygen • Nutrient Levels • Presence of Inhibitors • Microbial Interactions • Inoculation Practices • Winery Practices

  29. Winery Practices Impacting Microbial Flora • Sanitation Practices • SO2 • Cap Management • Nutrient Additions/Juice Adjustments • Maceration Strategy • Temperature of Fermentation

  30. To Encourage Grape Berry Wild Microflora • No or late inoculation with Saccharomyces • Add nutrients early (pre-inoculation) • Hold must/juice at low temperature • No to low SO2 • Adjust pH

  31. To Discourage Grape Berry Wild Microflora • Early addition of SO2,, other antimicrobials • Early inoculation with Saccharomyces • Use a high level of inoculum • Add nutrients after Saccharomyces is established • Avoid incubation at low temperatures

  32. Third Decision: How will fermentation be monitored?

  33. Fermentation Monitoring • What will be monitored? • How will it be measured? • How frequently will measurement be taken?

  34. Fermentation Factors to Be Monitored • Sugar consumption • Nitrogen availability/consumption • Microbial flora • Microbial activity • Acidity changes

  35. Monitoring Sugar Consumption • Hydrometry (specific gravity/density) • CO2 evolution (weight/pressure change) • Loss of glucose/fructose (HPLC, CE, enzyme assay) • Ethanol evolution (GC, eubillometry) • Temperature release

  36. Monitoring Nitrogen Levels • Amino acid analysis (HPLC) • Free amino nitrogen (FAN) • NOPA (nitrogen by OPA) • Yeast Utilizable Nitrogen (Hefeverwertbarer Stickstoff)

  37. Monitoring Microbial Flora • Microscopic observation • Total counts • Qualitative assessment • Plate counts • Total viable counts • Differential media

  38. Monitoring Microbial Activity • Volatile acidity analysis • Vinyl phenols • Hydrogen sulfide • “Sniff” test • By nose • Must be sensitive to off-characters

  39. Monitoring Acidity Changes • Titratable acidity • pH • Enzymatic assay • HPLC • Paper chromatography • Malate • Tartrate • Lactate

  40. Monitoring Strategy • Ease vs. Frequency • Cost • Skill level required/Difficulty of analysis • Is information necessary?

  41. Fourth Decision: Temperature of Fermentation

  42. High Fermentation Temperatures • Speed fermentation rate • Discourage diverse flora • Enhance extraction (reds) • Greater loss of volatile aroma characters • May increase risk of stuck fermentation

  43. Low Fermentation Temperatures • Favor non-Saccharomyces flora • Better retention of volatile aroma compounds • Slow fermentation rates

  44. Fifth Decision: Fermentation vessel

  45. Fermentation Vessel • Wooden cask • Size • Source of wood: Oak? Redwood? • Stainless steel tank • Refrigeration • Size • Barrel • Age • Type of Oak • Cement

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