1. Lecture 11: Stuck Fermentations: Diagnosis and Rectification

2. In this lecture we will learn how to recognize an arrested fermentation, how to diagnose the cause of the problem and how to re-initiate fermentation

3. Normal Fermentation Profile Glucose is consumed faster than fructose Arrested fermentations will be high in fructose relative to glucose

5. Problem Fermentation Profiles

7. Types of Sluggish Fermentations Long Lag

9. Causes of Long Lag Poor health of starter culture Presence of inhibitors Poor grape quality –Mold infestation –Premature initiation of fermentation

10. Poor Health of Starter Culture Active Dry Yeast: Past expiration date Not hydrated properly Not stored properly Natural Fermentation: Yeast numbers low Inhibitory microbes present Poor yeast strain present

11. Presence of Inhibitors Sulfur dioxide concentration too high Sulfur dioxide added improperly Microbial activity resulting in inhibition Pesticide/fungicide residues on grapes at harvest Temperature of must/juice too high/low

12. Poor Grape Quality Infected grapes: loss of micronutrients Infected grapes: high microbial loads Loss of free oxygen

13. Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation

15. Causes of Slow Rate Over Entire Time Course Failure to reach maximum cell density Nutrient (growth factor) limitation Strain a poor choice for conditions Inhibitory fermentation conditions: temperature, pH, ionic imbalances

16. Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation Rapid Rate Becoming Slow

18. Causes of a Decrease in Rate Poor ethanol tolerance Loss of viability Loss of fermentative capacity Nutrient (survival factor) limitation Poor strain

19. Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation Rapid Rate Becoming Slow Abrupt Stop

21. Causes of an Abrupt Stop Temperature shock Rapid build up of inhibitors: acetic/organic acids pH decreases too much Strain very ethanol sensitive

22. Most Common Causes of Stuck/Sluggish Fermentations Nutrient deficiency Temperature extreme Presence of a toxic substance Microbial incompatibility Deficient yeast strain Poor fermentation management decisions

23. Why are stuck fermentations difficult to treat? Cells adapt to adverse conditions by reducing fermentation capacity Biological adaptation difficult to reverse Diagnosis of cause of fermentation problem difficult Conditions that cause stuck fermentations are also conducive to cell death New inocula respond to cell death by arresting activities

24. Fermentation Variables Impacting Progression and Rate Oxygenation

25. Oxygen is a micronutrient electron acceptor Oxygen is a survival factor Oxygen can lead to color changes (brown, pink, orange)

26. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted

27. Mixing Separates yeast from end products Brings yeast in contact with new nutrients Can facilitate skin extraction in reds and solids extraction in whites and reds

28. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel

29. Fermentation Vessel Stainless steel can be cooled Stainless steel easier to sanitize Stainless steel is inert Wood: Can impart positive flavors and aromas Wood: Difficult to clean; impossible to sterilize Wood: Develops stable biofilm of microflora

30. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel Inoculation Practices

31. Spontaneous Fermentation Inoculated Fermentation

32. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel Inoculation Practices Temperature of fermentation

33. Temperature Affects presence and persistence of wild flora Affects fermentation and growth rates Extremes are inhibitory Impacts spontaneous chemical reactions

34. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel Inoculation Practices Temperature of fermentation Supplementation/Juice treatments

35. Supplementation Prevents nutritional deficiency May impact spectrum of yeast end products Residual nutrients encourage growth of spoilage organisms Unwanted byproducts may be made

36. Juice/Must Supplements Diammonium phosphate (0.96 g/L; 8 lbs/1000 gal) Yeast nutritional supplements (varies by producer) Yeast autolysates (3lb/1000 gal) Thiamin hydrochloride (0.005 lb/1000 gal)

37. Other Juice Treatments Fining Centrifugation Aeration Clarification: settling/filtration

38. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel Inoculation Practices Temperature of fermentation Supplementation/Juice treatments Lees contact

39. Grape Lees Contact Extraction of nutrients Extraction of grape characters Function as solids

40. Fermentation Variables Impacting Progression and Rate Oxygenation Mixing: natural or assisted Type of Fermentation Vessel Inoculation Practices Temperature of fermentation Supplementation/Juice treatments Lees contact Presence of solids

41. Presence of Solids Natural (grape material) or added (bentonite, yeast hulls) Stimulate fermentation Stimulate growth Source of nutrients Removal of inhibitory components

42. Re-initiation of Stuck Fermentations Correct diagnosis of nature of the problem important If re-inoculating, make sure inoculum is adapted to conditions of stuck wine Serial re-inoculation May need to remove existing biomass

43. Serial Re-Inoculation Fresh Juice Arrested Wine

44. Serial Re-Inoculation Transfer initial 50:50 blend to second tank when it is 2-4 Brix above the arrested Brix level of the stuck fermentation Do not let any of the intermediate steps in the series go dry, transfer them at the equivalent or slightly higher Brix than the arrested wine

45. This concludes the section on the alcoholic fermentation.