ABSTRACT
Yeasts are eukaryotic microorganisms classified as members of the fungus kingdom with 1,500 species currently identified and are estimated to constitute 1" of all described fungal species. Saccharomyces cerevisiae is one of the best genetically characterised yeast as its genome is fully sequenced and analyzed exhaustively. In contrast, brewer's yeast is refractory to the genetic procedures used with laboratory strains. The main reason is its low sexual fertility. Early attempts to carry out conventional genetic analysis with brewer's yeast faced the problems of poor sporulation and low viability. To overcome this difficulty, several researchers hybridized brewing strains with laboratory strains of S. cerevisiae. Yeast and barley play an active, primary role in the brewing process. The other two beer ingredients, water and hops, have secondary roles. Yeast is the fermenting agent, which transforms the carbohydrates stored in the grain of barley into ethanol. Flocculation is a cell adhesion process mediated by the interaction between a lectin protein and mannose.
