Brewer's yeast belongs to the yeast genus. In wort, through the external cell membrane, they will absorb dissolved sugars, simple nitrogen substances, vitamins, ions and other substances, and then they use these substances through metabolic pathway, for their own growth and fermentation, and produce rich beer flavor substances at the same time. Therefore, yeast is the main player of beer fermentation and the soul of beer brewing. The type and quality of yeast determine the type and flavor of beer.