Metabolic and Morphological Evaluation of Two Brewer’s Yeast Strains Throughout Serial Re-Pitching in Beer Fermentation

Beer fermentation is the process of growing yeast anaerobically in a malt-based medium, ultimately resulting in alcohol and carbon dioxide production. In order to reduce the cost and waiting time, serial repitching has been practiced among microbrewers. The technique emphasizes transferring yeast from one batch of beer to the subsequent brewing cycles. It has been shown that aged yeast cultures have higher fermentation efficiency and shorter lag period, thereby resulting in shorter fermentation times, faster pH drop, and lower concentrations of unwanted products. Despite the advantages of serial repitching, one can only practice repitching for approximately 5-6 times with a good starting culture due to the decrease in brewing efficiency. In this study, we sought to further investigate the metabolic activity and morphological change of two brewer’s yeast strains: London ale WLP013 and Czech Budejovice lager WLP802 throughout 8 batches of fermentation. At the end of each batch, samples were collected and subjected to YT plate and flow cytometry testing. Even though there was no significant difference in alcohol by volume throughout 8 batches, principle component analysis indicated that there were changes in metabolic potential after each batch of fermentation in the two brewer’s yeast strain. Maltose, maltotriose and sucrose were common substrates correlated to these changes between strains. Czech Budejovice lager WLP802 exhibited a decrease in flocculation after eight batches, while London ale WLP013 remains at the same level of flocculation throughout eight cycles of fermentation. The findings in this study suggest that YT plate can be used as a platform to identify when brewer’s yeast undergo a massive shift in metabolic potential