Saccharomyces and Non-Saccharomyces Starter Yeasts

This chapter describes the importance of yeast in beer fermentation. Initially, the differences between Saccharomyces cerevisiae and Saccharomyces pastorianus in the production of "ale" and "lager" beers are analyzed. Then, the relationships between beer nutrients and yeast growth are discussed, with special emphasis on the production of the flavor compounds. The impact of the wort composition on flocculation is also discussed. Furthermore, conventional approaches to starter yeast selection and the development of genetically modified microorganisms are analyzed. Recent discoveries relating to the use of S. cerevisiae strains isolated from different food matrices (i.e., bread and wine) and the potential for the use of non-Saccharomyces starter strains in beer production are discussed. A detailed review of the selection of starter strains for the production of specialty beers then follows, such as for gluten-free beers and biologically aged beers. Yeast recovery from top-cropping and bottom-cropping systems and the methodologies and issues in yeast propagation in the laboratory and brewery (i.e., re-pitching) are also analyzed. Finally, the available commercial preparations of starter yeast and the methods to evaluate yeast viability prior to inoculation of the must are analyzed.