Effect of serial repitching on the fermentation properties and condition of brewing yeast

On completion of a brewery fermentation, the yeast crop is removed from green beer, stored, and repitched. The effect of serial repitching on yeast inoculum condition and its subsequent fermentation performance is important but not well characterized. The physical properties of the brewing yeast cell surface influence flocculation and may be used to ascertain the physiological state of the cell. Cropped yeast from production and laboratory-scale fermentations have been examined. The effect of serial repitching on the physical properties of a production ale strain was monitored using dye retention, latex microsphere attachment, electron microscopy, and fluorescent dye techniques. The flocculation of each generation was determined. It was observed that a correlation between cell surface condition and fermentation performance existed. It is suggested that cell surface condition may be used to predict the fermentation performance of the subsequent pitch.