Genetic Instability in Flocculation of Bottom-Fermenting Yeast

Abstract

A long-term study of brewing yeasts used in production plants revealed that, among the many brewing properties of yeast, flocculation was most variable. With successive generations, flocculation tended to decrease, while other properties were generally unchanged. In many cases, genetic alterations such as chromosome deletion or loss in the flocculation gene Lg-FLO1, which governs flocculation of bottom-fermenting yeast, were shown by means of Southern- and Northern-blot analyses. Although flocculation of bottom-fermenting yeast is believed to be unstable, the mechanism of conversion from flocculation to nonflocculation is not clearly understood. This was the first time that the instability of flocculation in practical bottom-fermenting yeast was explained by genetic alteration. Genetic alterations such as observed in the Lg-FLO1 gene might occur frequently in brewing yeasts through successive generations, thereby affecting other aspects of brewing performance.