Can a Genetically Manipulated Yeast Strain Produce Palatable Beer?

Abstract

Diploid yeast strains have been produced containing a single gene for flocculation (FLO 4) and the intensity of the phenotypic expression of such strains has been found to vary, the flocculation intensity being modified or suppressed by an unknown factor(s). Although ale strains belong to the species Saccharomyces cerevisiae (melibiose negative) and lager strains to the species S. uvarum (carlsbergensis) (melibiose positive), hybridized diploids melibiose positive (MEL) and negative (mel) do not produce “typical” lagers and ales, respectively. It is concluded that ale and lager strains are polyploid cultures forming a small grouping within their species. The ability to ferment maltose and maltotriose is controlled by at least six polymeric gene systems (MAL genes). Each gene system's ability to out-ferment wort varies; MAL 6 is the most capable, whereas MAL 1 is incapable of using maltotriose. In the near future, it will be possible to construct yeast strains—probably polyploid in nature—capable of completely fermenting a wort in static culture and sedimenting out of suspension at the appropriate time. Although the problem of producing a palatable beer still remains, the use of polyploid yeasts may overcome these difficulties.