Effects of pH on Yeast Kinetics: Monastery Ale Strain
Maya Chandler
Yeast undergoes fermentation to convert glucose into ethanol and carbon dioxide. By-products such as ester, sulfur, and diacetyl are also formed, which can impact the flavor of the beer. Saccharomyces cerevisiae, also known as brewer’s yeast, generally prefers an acidic pH range of 5.0 to 5.2 for fermentation. Variations in environmental pH can reduce yeast viability and fermentation performance, as well as result in a sour, cloudy beer. Drops in the pH are observed as organic acids are produced; however, a significant reduction in pH can indicate contamination, further hindering yeast viability and performance. An increase in pH can indicate poor yeast performance due to a lack of available nutrients and can increase the risk of bacterial contamination. Different yeast strains can adapt to changes in environmental pH by stimulating proton ATPase pumps and altering gene expression. In this experiment, the wort pH was adjusted using baking soda to determine the effects on yeast kinetics in the Monastery Ale Strain from White Labs (Asheville, NC). The yeast slurry was repitched into freshly prepared wort for four generations to mimic industrial brewery conditions. Specific gravity, final gravity, days to final gravity, total cell counts, and viability were recorded throughout the fermentation process. Total cell counts between generations A, B, C, and D significantly differed due to the pH drop during fermentation. Total cell counts between batches M1, M2, M3, and M4 were not significantly different. Viability was not significantly different between generations or batches, indicating that the Monastery Ale strain could withstand changes in environmental pH. Days to final gravity were not significantly different between generations or batches, but slight variations in days to final gravity are critical for production schedules and profit in the brewing industry.
Maya Chandler is a biology major with psychology and chemistry minors, expecting to graduate in May 2023. She is a member of the Lander University's Honors College and is planning to attend graduate school for genetic counseling.