Transcript Introduction to Winemaking Part 3: Fermentation

Introduction to Winemaking
Part 3: Fermentation
Dr. James Harbertson
Extension Enologist
Washington State University
Fermentation
• Primary fermentation is conversion of sugar
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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
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
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
Jacketed Tank
CO2 Management
• Carbon dioxide is dangerous by-product
• How much is produced?
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 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.
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.
Example
• You have a 10,000 gallon tank of Chardonnay @ 24 Brix.
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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 @ 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!!!
Ventilation System
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
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.
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)
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.
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Isoamyl alcohol (banana)
Active amyl alcohol (?)
N-propyl alcohol
Phenyl ethanol (rose aroma)
Yeast Selection III
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Don’t 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
Wild Yeasts
• Examples: Kloeckera, Hansenula, Candida, Brettanomyces,
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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
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.
Stuck II
• Ethanol toxicity is common
• Cell membrane permeability is damaged
• Acidity inside cell  putting a load on membrane bound
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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.
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.
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
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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.
Copper Sheet
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.