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 s urface influences flocculation. Physiological stress, such as starvati on, affects the capacity of some strains to flocculate due to the reor ganisation of the cell wall and the modification of the surface physic al properties. On completion of a brewery fermentation, yeast is remov ed 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 s hown to cause yeast cell surface 'blistering'. Acid washing treatment was used to examine the susceptibility of the physical properties of t wo chain-forming brewing yeast Strains to stress. Although acid washin g 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 rat her than hydrophobicity influences the flocculation of chain-forming b rewing yeast.