Introduction to winemaking part 3 fermentation
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Introduction to Winemaking Part 3: Fermentation. Dr. James Harbertson Extension Enologist Washington State University. Fermentation. Primary fermentation is conversion of sugar into EtOH and CO 2 is carried out under anaerobic conditions. Anaerobic: Lacking oxygen

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Introduction to winemaking part 3 fermentation

Introduction to WinemakingPart 3: Fermentation

Dr. James Harbertson

Extension Enologist

Washington State University


Fermentation
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


Fermentation temperature
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
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



Co 2 management
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.


Co 2 management ii
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
Example

  • You have a 10,000 gallon tank of Chardonnay @ 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 @ 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!!!



Yeast selection
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
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
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
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)


Yeast selection iii
Yeast Selection III

  • 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
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


Stuck fermentations
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
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.


Stuck fermentations i
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
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.



Restarting a fermentation
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.