The performance of microbial populations is a function of the summed performance of their individuals, i.e. each cell contributes to the performance of the whole population. However, abiotic factors affect the physiological state and consequently the performance of each individual in a distinct manner, Thus, the efficiency of industrial microbial processes is boosted by cultivation strategies that improve the capacity of the living fraction within the bioreactor. Beer brewing processes are bounded to bioreactor scales up to more than 200 m(3). Subpopulations, indicating different physiological activities, should be considered as quickly and detailed as possible to avoid spoiling or diminishing the amount of the product. In this paper various subpopulations of a commercial yeast strain of Saccharomyces cerevisiae were characterised on three successive runs of brewing. Typical changes in structural and functional parameters of the cells were quantitatively analysed by multiparametric low cytometry and visualised by cell sorting and image analysis. (C) 2003 Elsevier Ltd. All rights reserved.