The Effects of Temperature Linda F. Bisson Department of Viticulture and Enology

1. The Effects of Temperature Linda F. Bisson Department of Viticulture and Enology University of California, Davis, CA

2. Outline of Presentation Impacts of Fermentation Temperature on Wine Composition Control of Temperature Temperature Optimization

3. Impacts of Fermentation Temperature in Red Fermentations

4. Impacts of Fermentation Temperature Extraction Volatilization Chemical Reactions Enzymatic Reactions Microbial Growth and Persistence

5. Extraction: Skin, Seeds, Stems • Extract anthocyanins from skin cells • Extract phenolic participants in co-pigmentation • Extract phenolic compounds that participate in stable pigment and tannin formation • Extraction of flavor components • Does seed extraction occur? • Impact of stem extraction (whole cluster ferments)?

6. AJEV (1987) 38(2):120-7

7. Location of Compounds in Berry Sucrose Glucose

8. Location of Compounds in Berry Malate Tartrate

9. Location of Compounds in Berry Phenols Phenolic compounds

10. Location of Compounds in Berry Potassium

11. Location of Compounds in Berry Inorganic anions

12. Factors Affecting Extraction: Cap Management • TEMPERATURE • TIME • MIXING • MACERATION • USE OF ENZYMES

13. Volatilization • Higher temperature = greater loss of volatiles • Impact depends upon reservoir of volatile compounds • Also impacted by vigor of yeast fermentation • Fermentation rates faster at higher temperatures

14. Chemical Reactions • Endothermic (heat absorbing) reactions go faster at higher temperature • Exothermic (heat releasing) reactions go slower at higher temperature • Some hydrolytic reactions stimulated by heat

16. Enzymatic Reactions • Some enzymatic reactions are endothermic, some exothermic • Heat can speed up or slow down enzymatic reactions • If too hot, enzymes lose structure and become inactivated

18. Hot Fermentations: Trade off between extraction of color and phenolic compounds and loss of aromatic components

19. Temperature and Microbes • Microbes have optimal temperatures for growth • Warmer favors bacteria • Warmer favors Saccharomyces over non-Saccharomyces wine yeasts • Warmer impacts ethanol tolerance

20. Temperature and Microbes • Temperature impacts: • Metabolic rates • Metabolite profiles • Cell leakiness • Tolerance to other stresses • Higher temperatures: higher ester formation but higher retention of off-esters (longer chain)

21. Control of Temperature

22. Control of Temperature • Fermentation is exothermic: rate of heat release directly proportional to rate of fermentation • If too hot, thermal death may occur and such fermentations are difficult to restart • ΔT (ºF) = 1.17 x Brix value, depends upon ambient temperature, vessel characteristics, surface to volume ratio, thermal conductivity of wall

23. Type of Cooling System • Tank type and size of jacket • Internal cooling • Coolant heat transfer coefficient • Coolant temperature

24. Tank Temperature • Temporal fluctuation: due to changes in metabolic activity • Fluctuation within tank • Cooler nearest the jacket, warmer in center • Warmer nearest the cap (enhanced metabolic activity) • Dependent upon mixing, cap management practices and temperature equilibration

26. Optimization of Fermentation Temperature

27. Optimization of Fermentation Temperature • Depends upon varietal • Depends upon style • Reliance on volatile compounds • Strength of reservoir of volatiles

28. Optimization of Temperature • To achieve optimal pigment extraction • To minimize loss of aromatic volatiles • To avoid spoilage organisms • To prevent arrest of fermentation

29. Optimization of Temperature Influenced by: • Sulfite use • Vineyard flora • Winery flora • Site characteristics • Presence of rot/cluster damage

30. The Experiment: • Ferment Cabernet Sauvignon at four different temperatures: 60, 70, 80 90ºF • Examine color and sensory differences • Using TJ fermenters

32. Fermentation Curves of Cabernet Sauvignon

33. Temperature Flight • Glass 1: 60° • Glass 2: 70° • Glass 3: 80° • Glass 4: 90° • Glass 5: Mixture of all 4