Characterization of Hybrid Strains of Saccharomyces pastorianus for Desiccation Tolerance

This study examines the impact of desiccation on the viability and fermentation performance of multiple strains of Saccharomyces pastorianus. S. pastorianus is a hybrid resulting from a cross between S. cerevisiae and S. bayanus. It has been proposed that S. pastorianus can be categorized into two distinct types: S. pastoriemus-Saaz type, which has lost a significant amount of the genomic content contained within S. cerevisiae, and S. pastorianus-Frohberg type, which has retained almost all of the genomic content of S. cerevisiae. Both types of S. pastorianus, along with S. cerevisiae and S. bayanus strains, were desiccated by spray-drying and then rehydrated before assessing the extent of the damage to the cells. The viability of rehydrated cultures was determined using microscopic enumeration, capacitance, and plating. Fermentation performance was tested by inoculating equal amounts of viable rehydrated cells into brewer's wort and monitoring changes in cell count, carbohydrate utilization, and alcohol concentration until completion. The findings suggest that S. pastorianus-Frohberg type is less tolerant to desiccation than either S. cerevisiae or S. pastorianus-Saaz type. Selection of the correct type of S. pastorianus for use in active dry yeast could reduce the possibility of contamination or extended lag phases leading to stuck fermentations.