The impact of brewing yeast cell age on fermentation performance, attenuation and flocculation

Abstract

Individual cells of the yeast Saccharomyces cerevisiae exhibit a finite replicative lifespan, which is widely believed to be a function of the number of divisions undertaken. As a consequence of ageing, yeast cells undergo constant modifications in terms of physiology, morphology and gene expression. Such characteristics play an important role in the performance of yeast during alcoholic beverage production, influencing sugar uptake, alcohol and flavour production and also the flocculation properties of the yeast strain. However, although yeast fermentation performance is strongly influenced by the condition of the yeast culture employed, until recently cell age has not been considered to be important to the process. In order to ascertain the effect of replicative cell age on fermentation performance, age synchronised populations of a lager strain were prepared using sedimentation through sucrose gradients. Each age fraction was analysed for the ability to utilise fermentable sugars and the capacity to flocculate. In addition cell wall properties associated with flocculation were determined for cells within each age fraction. Aged cells were observed to ferment more efficiently and at a higher rate than mixed aged or virgin cell cultures. Additionally, the flocculation potential and cell surface hydrophobicity of cells was observed to increase in conjunction with cell age. The mechanism of ageing and senescence in brewing yeast is a complex process, however here we demonstrate the impact of yeast cell ageing on fermentation performance.

Effects of Fermentation Parameters and Cell Wall Properties on Yeast Flocculation1

“…9). This result indicates old cells, due to their bigger size and higher levels of zymolectins, should be more flocculent as has been reported previously 27,28 .…”

Exploring the lag phase and growth initiation of a yeast culture by means of an individual-based model

“…Within the stated limitations, this study mimics the industrial production of beer, which reuses yeast cropped at the end of fermentation in subsequent fermentations, so the immediate and long term fermentation performance is conditioned by the characteristics of these reused inocula. Since the yeast Saccharomyces cerevisae has a limited replicative lifespan, each cell within a population is only capable of a finite number of divisions prior to senescence and death (Powell et al, 2000(Powell et al, , 2003. Towards the end of fermentation yeast sediments and are collected within the fermenter cone.…”

“…At the end of a fermentation a portion of the yeast is removed from the fermentation vessel for 'serial repitching'. Typically this is the centre-top portion of the yeast crop, theoretically comprising middle-aged and virgin cells (Powell et al, 2003).…”

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

“…Both these parameters have been reported to affect the flocculation potential of yeast. For three industrial yeast strains fractioned into virgin-rich and mother-rich pools, the virgin-rich pool had a lower flocculation potential (25-46%) compared to the mother-rich pool (51-87%) 58 . Several differences between the cell surfaces of virgin and replicatively aged cells may explain the difference in flocculation potential.…”