Some Considerations of the Flocculation Characteristics of Ale and Lager Yeast Strains*

Abstract

While some ale yeast strains are able to flocculate when cultured in a defined medium of glucose, ammonium salts, vitamins and ions, others require the presence of a nitrogen-containing inducer in the growth medium. On the other hand, all flocculent lager strains examined to date are able to flocculate after being cultured in a defined medium and do not appear to require the addition of inducer material to the growth medium. The inducer material present in wort has been identified as peptide. By the use of ion exchange chromatography the peptide fraction that induces flocculation has been found to contain a high level of acidic amino acid residues with a very similar structure to that reported for the a-factor involved in sexual agglutination of haploid a. and a cells of Sacch. cerevisiae.Studies on the adsorption of Ca++ ion by the cell wall failed to reveal any significant differences in total uptake between flocculent and non-flocculent cultures. It would appear that Ca++ ions are bound less tightly by non-flocculent cells than by flocculent cells. The contribution of calcium to flocculation is not the absolute amount of this ion adsorbed by the yeast cell wall but rather the stereo-specific manner by which it is bound, i.e., its position relative to the three-dimensional structure of the yeast cell wall.

Role of Wall Phosphomannan in Flocculation of Saccharomyces cerevisiae

“…Mill (1964b) largely agreed with Harris (1959) but suggested that the floc is stabilized by co-operative hydrogen bonding involving hydroxyl groups on the cell-surface polysaccharide. Recent work by Stewart, Russell & Garrison (1975) furnished additional evidence for the formation of carboxyl-Ca2+ complexes in yeast flocs, and they suggested that the carboxyl groups involved are in acidic wall proteins. Lyons & Hough (197oa, b, 1971), on the other hand, believe that the anionic groups involved are mainly, if not solely, in the phosphodiester linkages in the wall mannan (Ballou, 1974(Ballou, , 1976.…”

Flocculation of Brewers, Yeast

“…This considerable difference could be associate with requirement of strain to some compound(s) in wort that induce floes formation (14). One of the major differences between defined medium and wort is the presence of proteins, peptides and amino acids in the former.…”

The Horace Brown Medal Lecture: Forty Years of Brewing Research

“…It has also been suggested that cell walls isolated from flocculent cultures bind more Ca ++ ions than walls isolated from non-flocculent cultures. Employing radiolabelled Ca 45 , studies have been conducted to compare the calcium binding ability of a number of ale and lager flocculent and non-flocculent brewer's yeast cultures 150,151 . When the final calcium uptake of each culture was analysed (Table I), it was clear that no direct correlation existed between the total calcium adsorbed and flocculation.…”