The influence of inoculum form, age, and temperature on the viability of yeast intended for home brewing purposes
Mentor:Michael Nicholson, Adjunct Professor of Biology, Oxnard College
Home brewers use packaged yeast (Saccharomyces cerevisiae) for the production of beer and wine. Since yeast viability dramatically impacts fermentation, home brewers are concerned with the factors that might influence it. The purpose of this study was to investigate packaged yeast viability as influenced by yeast inoculum form (dry or liquid), age (fresh or 2-year old), and temperature (70˚F, 100˚F, and 130˚F). Volumeters were used to measure CO2 production of all possible combinations of treatments. Each volumeter contained 15 ml of yeast slurry (1x108 cells/ml). Production of CO2 was measured over approximately 17 hours, and the hourly average rate of CO2 production established the data set. A factorial MANOVA supported the alternate hypothesis (HA) that the three factors under study each contribute to differences in CO2 production (all possible combinations, α = 1% significance), while individual one-way ANOVAs explored specific pairs of factors to elucidate subtle differences between groups. The fresh liquid yeast performed best, overall, at 70˚F and 100˚F, but failed at 130˚F, while old liquid yeast performed worst, failing at all treatment temperatures. The fresh dry and old dry yeast performed at all temperature treatments, with fresh outperforming old consistently, and with better performance with decreased temperature treatments. These findings indicate that the home brewer, using packaged yeast, should definitely consider yeast format, age, and temperature when preparing to brew. Specifically, because fresh liquid yeast packages appear to be more sensitive to temperature and have a shorter shelf life than dry yeast packages, it is important to keep them cool and use them as soon as possible after purchasing them. Dry yeast packages may be better options for those who need a supply of yeast on-hand for use in the future, or for those who cannot keep the packages cool while transporting them after purchasing them.