Serial repitching, the process of reinoculating a previously used yeast culture in a fresh wort, is a procedure very common in large industrial brewing protocols. In commercial applications, yeast may be serially repitched from 6 to a dozen or more times, depending on the size of the brewery. The impact on yeast health, fermentation lag time, fermentative ability and sugar metabolism has been examined previously, but the results have been varied. A serial repitching experiment using a commercially available brewing yeast was conducted. We monitored sugar utilization for glucose polymers up to 9 in length over nine generations using three separate fermentors. The purpose of this project was to see if glucose polymer metabolism patterns evolve as the yeast <i>S. cerevisiae </i>ages. We found that serial repitching has a direct effect on the utilization of maltotetraose, a 4 hexose unit sugar, and no effect on the utilization of glucose, maltose, and maltotriose. While there was no metabolism of maltotetraose in the first two generations of <i>S. cerevisiae</i> fermentation, all subsequent generations showed significant utilization of maltotetraose – up to 95% of the total present. This exclusive maltotetraose utilization pattern provides evidence that serial repitching may cause yeast to express specific and previously unidentified dextrin metabolizing enzymes as the generation number of the yeast increases.

Utilization of maltotetraose during a nine generation serial repitching experiment

2019 Spring National Meeting

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