Date of Award
Fall 9-22-2021
Degree Type
Thesis
Degree Name
Master of Science in Integrative Biology (MSIB)
Department
Biology
Committee Chair/First Advisor
Dr. Christopher Cornelison
Major Professor
Dr. Christopher Cornelison
Second Committee Member
Dr. Martin Hudson
Third Committee Member
Dr. Jonathan McMurry
Fourth Committee Member
Dr. Melanie Griffin
Abstract
Secondary fermentation of beer is traditionally used to condition and refine the sensory profile of a beer. During methods such as barrel aging or lagering, the yeast continues to produce flavor-active compounds. Some methods include the intentional inoculation of microorganisms or the utilization of natural consortia associated with a barrel, fruit, or additive for the generation of desired sensory profiles. As unique products increase in popularity, brewers have begun to experiment with secondary fermentation using alternative yeast species as bioflavorants. To assess the viability of an organism’s application to brewing, the physiochemical properties of beer and their impact on the growth of the organism must be considered. This study examines the effect of a range of physiochemical conditions present in the product of a primary fermentation prepared for secondary fermentation on the growth of a series of yeasts not conventionally used in brewing. This study also compares the resulting sensory-active metabolites present in beers secondarily fermented with non-conventional yeasts. The results from this research provide insight into the potential role of these species for targeted inoculation in secondary fermentation. Seventeen yeast species from thirteen different yeast genera were studied. Yeast were grown in malt extract media to measure growth compared to Saccharomyces cerevisiae over a 36-hour period. Growth was assessed using a hemocytometer for enumeration. Replicate experiments were performed with lactic acid, ethanol, and hop content in various concentrations to replicate conditions found in a product ready for secondary fermentation. Additionally, headspace aroma profiling of beers secondarily fermented with the studied species was conducted via SPME-GC-MS to elucidate the contributing volatile constituents. The evaluated species showed distinct growth profiles related to physiochemical conditions and distinct volatile organic compound profiles indicating a differential utility as secondary fermenters and bioflavorants based on standard beer style parameters. Cumulatively, this study allows for a more targeted understanding on the contribution to non-conventional yeasts in brewing.