Brewing Yeast Physiology
Characterization of the genomes of yeast belonging to the genus Saccharomyces, including those used in brewing, has been the subject of intense investigation. Fundamental differences between ale and lager strains have been demonstrated. The linkage of many genes with cellular function has been made. Although essential, this has also highlighted a fundamental lack of knowledge as to how expression of the genome is made manifest in terms of phenotype, in particular how the phenotype is regulated at the level of the metabolome. The intention of this chapter is to review current research that has been directed towards these ends. The chapter addresses how yeast physiology is influenced by the conditions it is exposed to in current modern brewing practice, what are the potential pitfalls, and how can processes be managed to increase the likelihood of a controlled and consistent outcome. Of particular note are the factors that influence passage of cells into and out of quiescence, coincident with fermentation initiation and eventual removal of cropped yeast to storage. Since the majority of published studies have used haploid laboratory strains grown aerobically on semi-defined media, attempts have been made to extrapolate results to encompass brewing strains serially re-pitched in semi-aerobic fermentations using wort as the feedstock.