Brewer’s yeast: genetic structure and targets for improvement

The art of beer brewing is ancient, and Saccharomyces yeast probably played a pivotal role from the beginning. Production of beer from the barley grain consists of multiple steps, of which only the last few involve the yeast. Nevertheless, the behaviour of the yeast is highly decisive for both speed and outcome of the whole process, and to a large extent influences the total beer flavour profile. Long known fermentation-related problems as well as the occasional evolution of certain offflavours can be blamed on the yeast. Great efforts have therefore gone into studies of the genetics of brewing yeast, starting with the pure cultivation of lager brewing yeast more than 100 years ago and continuing with today’s detailed description of the brewing yeast genome, as well as ventures into genetic modification to solve brewing problems. Here we describe current knowledge on brewing yeast genetics and phylogeny, fields, which have developed with an increasing speed during the last couple of decades. Further, we portray the genetic technologies that are available for the yeast breeder in his or her endeavours for strain improvement. Major areas for the improvement of the brewing yeast behaviour are discussed, and the scientific bases for past and current efforts to solve these problems by genetic approaches are described, as well as the strategies employed. Finally, we speculate on the future of brewing yeast modification, and take into consideration the great landmarks in yeast research during the last couple of decades. We also briefly discuss matters of public perception of genetically modified brewing yeast.