MBAA TQ https://doi.org/10.1094/TQ-58-2-0414-01 | 
VIEW ARTICLE
Luis F. Castro and Nichole Bryant. Department of Food Science and Nutrition, California Polytechnic State University, San Luis Obispo, CA 93407, U.S.A.
Abstract
A laboratory-scale study on the effects of wort gravity (10, 14, and 18°P), international bitterness unit (IBU) levels (25, 50, and 75 IBU), and serial repitching on the viability of an ale yeast was conducted. Serial fermentations of worts with different gravity and IBU levels were performed in the laboratory. Analysis of variance showed that all three main factors had a significant effect (P < 0.05) on yeast viability. It was observed that increases in wort gravity led to lower yeast viability levels at the end of the fermentation cycle, and a decrease in viability was also observed as repitching cycles increased in medium (14°P) and high (18°P) gravity worts. Based on the results, the number of times the ale yeast could be repitched into 10°P wort is higher compared with 14 and 18°P worts. Increases in IBU levels resulted in lower yeast viabilities over increasing wort gravity levels and repitching cycles. Results showed that the number of times yeast could be repitched into 14 and 18°P worts was lower at all IBU levels when compared with 10°P wort. The study also found that ethanol production was significantly affected (P < 0.05) by repitching cycle and wort gravity level but not by IBU level. While this study did not pretend to mimic production conditions, results strongly suggest that brewers should be aware of the impact of environmental conditions such as wort gravity, IBU, and repitching cycles on yeast viability and performance, and they should always monitor viability in order to produce quality products consistently.
Keywords: alcohol by volume, beer, yeast, bitterness, viability, high-gravity brewing
