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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 into EtOH and CO 2 is carried out under anaerobic conditions. Anaerobic: Lacking oxygen

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Introduction to Winemaking Part 3: Fermentation

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  1. Introduction to WinemakingPart 3: Fermentation Dr. James Harbertson Extension Enologist Washington State University

  2. 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

  3. 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

  4. 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

  5. Jacketed Tank

  6. 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.

  7. 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.

  8. 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!!!

  9. Ventilation System

  10. 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

  11. 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.

  12. 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)

  13. 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)

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Copper Sheet

  21. 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.

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