Diagnostic Key Tips to Assure Completion of Fermentation
Tips to Assure Completion of Fermentation
- Select the correct strain for the conditions: Many fermentation problems would have been easily avoided by selecting the proper strain for the fermentation conditions. A simple calculation to predict final ethanol yield can be used to make sure the strain selected as inoculant has sufficient ethanol tolerance to attain the final ethanol concentration. If it does not, it will be nearly impossible to get the strain to complete the fermentation. Similarly if the strain has high nutrient demands or low pH or temperature tolerance it should not be used under conditions where those stressors are likely to exist or evolve.
- Yeast talk to each other: All microbial populations engage in population signaling and Saccharomyces is no exception. Generation and response to starvation signals allows cells that are currently in a nutrient sufficient microenvironment to anticipate an impending shortage of nutrients and to shut down cell growth and metabolism and enter a survivalist state. Even if the original cause of the signal has been alleviated if the initial biomass is still producing an alarm signal newly introduced biomass will respond to the signal and shut down metabolism. Cell lysis can also send a signal of cell death to the population and lead the rest of the population to shut down to avoid a similar fate. If cell death is evident the wine should be racked off of the yeast lees prior to reinoculation.
- Stresses compound exponentially: Yeast cells are more sensitive to a stress factor if other stress factors are simultaneously present. Stress tolerances largely involve the same set of stress response proteins and if the capacity of these response factors to correct the damage is exceeded tolerance will not occur. Yeast therefore have a limited capacity to mitigate stress damage. The more stresses that are present in the environment the more varied the damage and the greater the demands on cellular damage mitigation processes. Seemingly moderate stress when combined with other types of stresses can lead to fermentation arrest.
- Provide a stable physical and chemical environment: Swings in pH and temperature can negatively impact fermentation progression. It is easier to gradually adapt to a changing environment than to have to abruptly adapt. This again is due to a limited capacity to repair damage, turn over proteins and synthesize new ones.
- Monitor non-Saccharomyces populations: Blooms of non-Saccharomyces organisms during fermentation or before fermentation is completed can lead to arrest of fermentation. The presence of other organisms can often be detected by an unusual aroma of the fermentation. Unusual aromas should not be ignored. A microscopic examination of the fermentation should be conducted and action taken to limit the non-Saccharomyces populations.
- Provide adequate nutrition: Juice nutrient contents should be assessed to avoid fermentation problems. It is important to remember that nutrient needs increase with increasing sugar content of the must and as the ethanol tolerance limit of the strain is approached. Feeding the fermenting population is important. Feeding competitor microbes should be avoided. Remember that oxygen should also be viewed as a nutrient.
- Time is of the essence: The conditions that lead to sluggish and arrested fermentations will also eventually lead to cell death. Rapidly correcting inhibitory conditions will increase the likelihood of a spontaneous restart as well as the chances of a successful reinoculation. Waiting also allows for compounding factors to occur such as the bloom of spoilage organisms or increased opportunity for oxidation.