Many microbreweries practice serial fermentation, or serial repitching. Serial repitching is the process by which one yeast culture is reused for multiple batches of beer. Each batch of subsequent beer is called a “pitch.” This technique helps breweries limit production costs. However, fermentation is difficult to predict throughout serial fermentation. This leads to beer quality issues such as fluctuation in alcohol production, buildup of unwanted flavor compounds, and decreased carbon dioxide production, which results in reduced profit. To combat this issue, many breweries will attempt to predict fermentation efficiency through viable cell counting in order to ensure a consistent number of viable cells are inoculated into each pitch. However, it has been previously demonstrated by researchers and brew masters that viability and other morphological characteristics are not a reflection of metabolic competence in brewer’s yeast (Saccharomyces cerevisiae). For this reason, a better understanding of serial fermentation at a molecular level is necessary. Once the molecular impacts of serial repitching are understood, specialized strains of brewer’s yeast can be designed to provide more stable, predictable fermentation. This study investigated whether MAL genes, which encode the enzyme maltase, exhibits a decrease in mRNA expression throughout serial fermentation via RT-qPCR. Additionally, the present study investigated telomere integrity throughout serial fermentation to determine whether telomeres degrade throughout serial repitching via telomere restriction fragment analysis (TRF). No significant decrease in MAL mRNA expression was observed as pitch number increased. This indicates that reduced maltase expression is not the cause of decreased fermentation efficiency. Telomeres shortened and became more heterogeneous in length throughout serial fermentation. These observations indicate that increased pitch number results in cell aging and an overall decline in cell health.
Date of Degree
Master of Science (MS)
Science, Engineering and Technology
Bennett, D. (2021). Investigation of fermentation efficiency in Saccharomyces cerevisiae through telomere integrity and maltase expression [Master’s thesis, Minnesota State University, Mankato]. Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato. https://cornerstone.lib.mnsu.edu/etds/1137/
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