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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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Reading Assignment:

Text, Chapter 4, pages 102-126


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


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First Decision: impacting yeast fermentation performance and strategies for management of the fermentation.

To inoculate or not to inoculate?


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Sources of impacting yeast fermentation performance and strategies for management of the fermentation.Saccharomyces

  • Vineyard flora

  • Winery flora

  • Inoculum


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Inoculated Fermentations impacting yeast fermentation performance and strategies for management of the fermentation.

  • With active dry yeast (ADY)

  • With a starter culture in juice

  • With an already fermenting must/juice


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Level of Inoculum impacting yeast fermentation performance and strategies for management of the fermentation.

Typically 105 - 106 cells/ml or 1 to 0.1% on a volume/volume basis


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Native Flora Fermentations impacting yeast fermentation performance and strategies for management of the fermentation.

There is no deliberate inoculation with Saccharomyces


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Inoculated Fermentations: The Benefits impacting yeast fermentation performance and strategies for management of the fermentation.

  • Predictability

  • Control of spoilage characteristics

  • Yeast Neutrality: enhanced varietal characteristics


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Inoculated Fermentations: The Negatives impacting yeast fermentation performance and strategies for management of the fermentation.

  • Neutrality: Reduced overall complexity

  • Fermentation rates too rapid

  • Wine too “yeasty”


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Native Flora Fermentations: The Benefits impacting yeast fermentation performance and strategies for management of the fermentation.

  • Increased microbial complexity

  • Slower fermentation rates


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Native Flora Fermentations: The Negatives impacting yeast fermentation performance and strategies for management of the fermentation.

  • Off-character formation (non-Saccharomyces organisms)

  • Lack of predictability

  • Seasonal variation in microbial populations on fruit


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Second Decision: impacting yeast fermentation performance and strategies for management of the fermentation.

Encourage or discourage grape berry microflora?


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Grape Berry Microflora impacting yeast fermentation performance and strategies for management of the fermentation.

  • Bacteria

    • Bacillus

    • Pseudomonas

    • Micrococcus

    • Lactic Acid Bacteria

    • Acetic Acid Bacteria

  • Molds

  • Yeast


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Grape Berry Microflora impacting yeast fermentation performance and strategies for management of the fermentation.

  • Bacteria

  • Molds

    • Aspergillus

    • Penicillium

    • Rhizopus

    • Mucor

    • Botrytis

  • Yeast


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Grape Berry Microflora impacting yeast fermentation performance and strategies for management of the fermentation.

  • Bacteria

  • Molds

  • Yeast

    • Kloeckera/Hanseniaspora

    • Metschnikowia pulcherrima

    • Hansenula species

    • Candida species

    • Saccharomyces


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Grape Berry Microflora impacting yeast fermentation performance and strategies for management of the fermentation.

  • 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


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Factors Affecting Grape Berry Microflora impacting yeast fermentation performance and strategies for management of the fermentation.

  • Rainfall/ Humidity

  • Insect vectors

  • Altitude

  • Temperature

  • Vineyard fertilization practices

  • Varietal factors: tightness of cluster

  • Vineyard practices: inoculation of fruit with soil microbes


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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)


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

    • Low temperatures inhibit bacteria

    • Low temperature enriches for non-Saccharomyces yeasts


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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


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

  • Oxygen

  • Nutrient Levels

    • Must/Juice composition

    • Supplementation

    • Timing of addition


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

  • Oxygen

  • Nutrient Levels

  • Presence of Inhibitors

    • Fungicide/pesticide residues

    • Sulfur dioxide


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

  • Oxygen

  • Nutrient Levels

  • Presence of Inhibitors

  • Microbial Interactions


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Types of Microbial Interactions Must/Juice

  • Production of inhibitors

    • Acetic acid

    • Ethanol

    • Fatty acids

    • Killer factors

  • Competition for nutrients

  • Stimulation

    • Removal of inhibitor

    • Release of micronutrients


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

  • Oxygen

  • Nutrient Levels

  • Presence of Inhibitors

  • Microbial Interactions

  • Inoculation Practices


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Inoculation Practices Must/Juice

  • Early inoculation minimizes impact of wild flora

  • Higher levels of inoculation limit impact of wild flora


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Factors Affecting Persistence of Grape Berry Microflora in Must/Juice

  • pH

  • Temperature

  • Oxygen

  • Nutrient Levels

  • Presence of Inhibitors

  • Microbial Interactions

  • Inoculation Practices

  • Winery Practices


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Winery Practices Impacting Microbial Flora Must/Juice

  • Sanitation Practices

  • SO2

  • Cap Management

  • Nutrient Additions/Juice Adjustments

  • Maceration Strategy

  • Temperature of Fermentation


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To Encourage Grape Berry Wild Microflora Must/Juice

  • No or late inoculation with Saccharomyces

  • Add nutrients early (pre-inoculation)

  • Hold must/juice at low temperature

  • No to low SO2

  • Adjust pH


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To Discourage Grape Berry Wild Microflora Must/Juice

  • 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


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Third Decision: Must/Juice

How will fermentation be monitored?


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Fermentation Monitoring Must/Juice

  • What will be monitored?

  • How will it be measured?

  • How frequently will measurement be taken?


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Fermentation Factors to Be Monitored Must/Juice

  • Sugar consumption

  • Nitrogen availability/consumption

  • Microbial flora

  • Microbial activity

  • Acidity changes


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Monitoring Sugar Consumption Must/Juice

  • Hydrometry (specific gravity/density)

  • CO2 evolution (weight/pressure change)

  • Loss of glucose/fructose (HPLC, CE, enzyme assay)

  • Ethanol evolution (GC, eubillometry)

  • Temperature release


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Monitoring Nitrogen Levels Must/Juice

  • Amino acid analysis (HPLC)

  • Free amino nitrogen (FAN)

  • NOPA (nitrogen by OPA)

  • Yeast Utilizable Nitrogen (Hefeverwertbarer Stickstoff)


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Monitoring Microbial Flora Must/Juice

  • Microscopic observation

    • Total counts

    • Qualitative assessment

  • Plate counts

    • Total viable counts

    • Differential media


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Monitoring Microbial Activity Must/Juice

  • Volatile acidity analysis

  • Vinyl phenols

  • Hydrogen sulfide

  • “Sniff” test

    • By nose

    • Must be sensitive to off-characters


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Monitoring Acidity Changes Must/Juice

  • Titratable acidity

  • pH

  • Enzymatic assay

  • HPLC

  • Paper chromatography

    • Malate

    • Tartrate

    • Lactate


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Monitoring Strategy Must/Juice

  • Ease vs. Frequency

  • Cost

  • Skill level required/Difficulty of analysis

  • Is information necessary?


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Fourth Decision: Must/Juice

Temperature of Fermentation


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High Fermentation Temperatures Must/Juice

  • Speed fermentation rate

  • Discourage diverse flora

  • Enhance extraction (reds)

  • Greater loss of volatile aroma characters

  • May increase risk of stuck fermentation


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Low Fermentation Temperatures Must/Juice

  • Favor non-Saccharomyces flora

  • Better retention of volatile aroma compounds

  • Slow fermentation rates


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Fifth Decision: Must/Juice

Fermentation vessel


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Fermentation Vessel Must/Juice

  • Wooden cask

    • Size

    • Source of wood: Oak? Redwood?

  • Stainless steel tank

    • Refrigeration

    • Size

  • Barrel

    • Age

    • Type of Oak

  • Cement