Publication Date

Spring 2024

Abstract

Within the brewing community, there is a race to discover new ways to brew beers to create new flavor and smell profiles. Scientists across the globe are searching for novel species of yeasts which have the potential to enhance the flavor and smell of their beer. While most beers are brewed using one of a handful of domesticated yeast strains -- also known as pitching yeasts -- finding “wild” yeasts is one way to change fermentation products. Experimentation has been started on this front due to the wide array of properties that a wild yeast can change in a brew. For example, wild beers like the Belgium Lambic are often called sours due to a distinctive tart taste. This is achieved by adding bacteria, most commonly Lactobacillus, to the fermentation process to create lactic acid. Common flavors are fruity notes, maltiness, woodiness, and less common ones are citrus and peppery flavors. Yeasts can also determine the dryness of a beer. Many yeasts will also accentuate pre-existing flavors like honey and caramel and citrus. Discovery of new yeast strains adds variety to the brewing industry and partners the science industry with the commercial beverage industry.

In choosing the ideal strain for industrial usage, we are evaluating the potential strains with respect to temperature tolerance, pH tolerance, and ethanol tolerance. Fermentation temperature is easily standardized by the temperature of the surroundings around the fermentation vessel. Generally, brewing temperatures are within 9-14℃ for lagers and 15-26℃ for ales.These temperature ranges are conserved across a wide variety of the commonly used yeasts. Temperature parameters will determine the base flavor profiles which each strain produces. pH also works to influence potential flavor. The pH of beers change dynamically during fermentation; all ferments start at around pH 5 and changes are monitored over time. Since pH drops largely during fermentation, the final pH determines the flavor profile of the final beer. Lastly, ethanol tolerance is an indicator for the amount of final alcohol that the yeast produces. During the fermentation process, yeasts consume sugars in the ferment and produce carbon dioxide and alcohol. Fermentation will end and the alcohol concentration will be capped when the alcohol concentration exceeds the yeasts tolerance. A yeast which is able to tolerate a higher concentration of alcohol will continue to ferment for longer periods.

To discover new yeasts that might be appropriate for brewing, local fruits were harvested from Illinois Wesleyan University campus. The fruits collected were ground and strained. Cultures were isolation-streaked and grown on Yeast Peptone Dextrose (YPD) media with chloramphenicol at 30℃ for three days. The plates were then examined using colony morphology features which are consistent with known yeast. Once they were confirmed as yeasts, the cultures were analyzed using genetic tests and light microscopy imaging. Three isolates, which were confirmed as yeasts, were chosen for further work based on genetic identification and lab safety.

Disciplines

Biology

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