The Effect of Acid Washing and Fermentation Gravity on Mechanical Shear Resistance in Brewing Yeast

摘要

The effects of fermentation gravity and acid washing procedures on a brewing yeast strain's ability to resist mechanical shear in turbulent flow were investigated. Reynolds numbers of approximately 50,000 were calculated for experimental conditions with a specially developed pumping system. Higher-gravity fermentations lead to marginally increased, but statistically insignificant, cell rupture compared with lower-gravity fermentations. Cell populations remaining after shear application displayed marginally higher viability in higher-gravity fermentations. Acid washing procedures lead to an approximately sixfold decrease in cell viability compared with the controls. Cell wash water acidified with phosphoric acid lead to larger drops in viability than water alone. The addition of ammonium persulfate to an acid wash solution lead to increased viability losses when exposed to mechanical shear. β-(1→3)-Glucan in the cell wall was identified as contributing significantly to mechanical shear resistance.