Introduction to Winemaking Part 3: Fermentation

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Introduction to WinemakingPart 3 Fermentation

• Dr. James Harbertson
• Extension Enologist
• Washington State University

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Fermentation

• Primary fermentation is conversion of sugar into
  EtOH and CO2 is carried out under anaerobic
  conditions.
• Anaerobic Lacking oxygen
• C6H12O6 ?? 2CH3CH2OH 2CO2
• Heat is a by-product of reaction
• Yeast can be killed if temperature gets too high.
  Above 38?C problems occur.
• Fermentation temperature can be regulated
• CO2 is dangerous by-product that needs to be
  managed

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Fermentation Temperature

• Whites generally ferment at a lower temperature
  than reds.
• White fermentation temperatures
• Lower temp. to preserve volatile components
• Red fermentation temperatures
• Higher temp. for extracting phenolic components
  from skins and seeds

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Regulation of Fermentation Temperature

• Metal tanks (excellent conductor) can use jacket
  filled with coolant (ethylene glycol, ammonia)
• Wooden tanks (poor conductor) can use heat
  exchangers (uses tubes filled with cooler
  liquid, that when moved past warmer liquid trades
  temperatures). Requires external pump.
• Barrel fermentation temperature not controlled

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Jacketed Tank
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CO2 Management

• Carbon dioxide is dangerous by-product
• How much is produced?
• About 3 times the volume of liquid during one day
  of a slow fermentation.
• Fermentation rooms must have proper ventilation
• Cellar workers going into tanks should work in
  pairs
• CO2 detectors should be used in winery (Workplace
  safety have an upper limit of 0.5)
• Evolved CO2 also will remove off odors and
  pleasant ones.

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CO2 Management II

• Tank fermentations
• Ventilation system with a fan or blower
• Ferment in an outside tank
• Barrel fermentations-Inside
• Ventilation system required
• Air conditioning load to cool room is greatly
  effected by outside air.
• About 10,000 liters of CO2 produced by one
  complete barrel fermentation.

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Example

• You have a 10,000 gallon tank of Chardonnay _at_ 24
  Brix. How much CO2 will it make in one day if it
  produces 56 L CO2/L of juice fermenting at 1 Brix
  per day at 20?C?
• How much for an entire fermentation?
• (56 L CO2/(L of juice _at_ 1 Brix per day)
  (37,854.1 L/10,000 gallon tank) 2,119,824 L of
  CO2 2.2 million liters of CO2
• (2,119,824 CO2/Brix) 24 Brix 50,875,776 L of
  CO2
• 51 million Liters of CO2 will be produced in
  total!!!

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Ventilation System
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Yeast Selection

• Basic Criteria for selecting a yeast
• Fermentation vigor (rate of fermentation)
• Finishes fermentation to dryness
• Reproducible fermentation characteristics
• Ethanol tolerance
• Temperature tolerance
• Produces no off-flavors or aromas
• Sulfur dioxide tolerance

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Yeast Selection II

• Dried yeast are produced healthy under aerobic
  conditions with plenty of survival factors
  (saturated fatty acids, sterols)
• Healthy cell membrane for EtOH tolerance.
• Dried packets will survive for one year if stored
  in cold.
• Before addition to must, re-hydrate in a small
  volume of warm (40?C) water.
• Add about 0.1-0.2 g dry per L of must.

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Yeast by-products

• Aside from EtOH and CO2
• Glycerol-viscous by-product
• Not enough to modify wine mouth feel
• Elevated production in ? SO2 conditions
• Acetic Acid-vinegar (volatile acid)
• Normal production (100 to 200 mg/L) can be made
  from nutrient deficient musts
• Also made by spoilage organisms (Acetobacter)

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Yeast by-products II

• Higher Alcohols- higher MW higher BP
• Formation by breakdown of amino acids (removal of
  amino group at end of pathway).
• Excess amino acids does
• Also made from sugar breakdown
• Not enough to normally change aroma of wine.
• Isoamyl alcohol (banana)
• Active amyl alcohol (?)
• N-propyl alcohol
• Phenyl ethanol (rose aroma)

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Yeast Selection III

• Dont choose a yeast because it supposedly
  produces different aromas
• CO2 blows of most yeast volatiles during
  fermentation.
• Fermentation bouquet are unstable volatiles
  that can be achieved through cool fermentation
  and protected from air contact it can be
  maintained for about a week.
• Research showed no detectable differences between
  strains with same initial juice after
  fermentation was complete.
• During fermentation all lots of odors are
  detected but not after fermentation is complete.
• Only exceptions to this are wild yeasts and
  different species of Saccharomyces

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Wild Yeasts

• Examples Kloeckera, Hansenula, Candida,
  Brettanomyces, Zygosaccharomyces
• Can produce off aromas (horse sweat, feces)
• Compete with Saccharomyces
• Generally are SO2 and EtOH intolerant.
• Can be reduced by early SO2 addition and
  inoculation with Saccharomyces.
• Are temperature intolerant, at 25?C they are
  inhibited while Saccharomyces will survive up to
  38?C

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Stuck Fermentations

• Two classes Stuck and Stinky
• Some can be easily fixed, while others are more
  challenging.
• Causes EtOH toxicity, nutrient limitations,
  substrate inhibition, toxic substances and
  temperature shock.
• Monitoring Fermentation is key to catching a
  stuck or sluggish ferment.

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Stuck II

• Ethanol toxicity is common
• Cell membrane permeability is damaged
• Acidity inside cell ? putting a load on membrane
  bound enzymes required to remove it.
• Making more fatty acids to fix membrane requires
  O2
• Oxygen introduction (aeration) at beginning and
  at end of fermentation through stirring has been
  shown to these types of problems.
• A more ethanol tolerant Saccharomyces strain or
  species can also be used from the outset or
  brought in to finish the fermentation.

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Stuck Fermentations I

• Nutrient deficiency most common problem
• Nitrogen or phosphate deficiencies
• In some cases it is vitamin related
• Yeast strains display different sensitivities to
  nitrogen limitation.
• Nitrogen and phosphate can be added in form of
  diammonium phosphate (DAP) to adjust for
  deficiencies.
• 0.5 g/L usable nitrogen necessary for max yeast
  biomass and 0.2 g/L nitrogen for dryness.

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Stuck Fermentations II

• Stinky ferments (skunky, rotten eggs, garlic)
• Generally H2S, CH3SCH3 CH3SSCH3, CH3CH2SH
• Threshold µg/L range
• Unknown cause
• Linked to vitamin deficiency, elemental sulfur
  left on berries, free amino nitrogen deficiency,
  metal ions and perhaps sulfite.
• Copper sulfate can be used to remove H2S (less
  than 0.5 mg/L may be added with 0.5 mg/L residual
  US 0.2 mg/L other countries.

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Copper Sheet
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Restarting A Fermentation

• Start with fresh media and yeast
• Add in portion of the stuck ferment
• Allow for vigorous fermentation (adaptation)
• Add in stepwise fashion portions of stuck ferment
• Early diagnosis is key because it is more
  difficult to start stuck ferments that have gone
  full into full arrest.
• Plotting Brix depletion curve will show problem
  ferments.