Yeast physiological condition is known to influence fermentation performance, however, until recently cell age has not been considered as a brewing yeast stress factor. Cell ageing in Saccharomyces cerevisiae is determined by replicative, rather than chronological lifespan, and therefore the age of cells within a population is distinct from the culture age of pitching yeast. As brewing yeasts age they are subject to characteristic genetic, metabolic and morphological changes. Aged cells display an increase in size, reduced vitality and surface wrinkling. Younger individuals exhibit an extended generation time prior to division and are less tolerant to a variety of stress factors. In addition gene expression is known to alter throughout the lifespan. An age gradient is known to form within the cone of cylindro-conical fermenters during yeast sedimentation. It has been suggested that selection for cells of a particular age may occur during yeast cropping. The effects of cell age on fermentation performance are not known. Age synchronised populations of a lager strain (BB11) were prepared using sedimentation through sucrose gradients. Age synchronised populations were analysed to determine flocculation variability, using a modified Helm's assay, and the capacity to reduce diacetyl. Fermentations were performed using mini fermenters containing brewery wort (1060). Fermentation progression was monitored by measuring sugar utilisation in terms of weight loss over time. Diacetyl reduction was monitored towards the end of fermentation and the production of volatile compounds was determined in the final product. Virgin, mixed age and aged cell fractions produced significantly different fermentation profiles. Populations of undivided (virgin) cells were observed to ferment at a slower rate than mixed and aged cell fractions. Aged cell fractions fermented at a higher rate than mixed or virgin cell cultures. It is suggested that the extended generation time required prior to virgin cell reproduction causes a delay in the initial stages of fermentation. In addition, VDK reduction, volatile production and flocculation were observed to vary according to cell age. Aged individuals were observed to display a greater capacity to flocculate when compared to mixed age and virgin cell populations. It is suggested that the large size and cell surface morphology of older cells facilitates cell surface lectin-like interactions. Continual selection for a population with an imbalance of young or aged individuals during cropping may influence future fermentation performance and represent a source of fermentation inconsistency. It is hypothesised that selection for a population consisting of predominantly non-virgin cells may result in improved fermentation performance. It is suggested that 'warm' or 'early' cropping may facilitate the selection of such a population.