The importance of surface charge and hydrophobicity for the flocculation of chain-forming brewing yeast strains and resistance of these parameters to acid washing

The cell surface charge and hydrophobicity of the brewing yeast cell surface influences flocculation. Physiological stress, such as starvation, affects the capacity of some strains to flocculate due to the reorganisation of the cell wall and the modification of the surface physical properties. On completion of a brewery fermentation, yeast is removed from the beer, stored and inoculated (repitched) into a subsequent fermentation. Prior to repitching, brewing yeast slurries may be acid washed to remove any contaminating bacteria. This treatment has been shown to cause yeast cell surface ‘blistering’. Acid washing treatment was used to examine the susceptibility of the physical properties of two chain-forming brewing yeast strains to stress. Although acid washing affected the cell surface charge and hydrophobicity in both strains, the flocculation response was strain dependant. It is suggested that surface charge and the non-separation of progeny from mother cells rather than hydrophobicity influences the flocculation of chain-forming brewing yeast.