EFFECT OF SOME MONOVALENT AND DIVALENT METAL IONS ON THE FLOCCULATION OF BREWERS YEAST STRAINS*

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Abstract
In agreement with previous reports, it has been found that both Mg++ and Mn++ ions can imitate Ca++ as inducers of flocculation, though the intensity of the flocculation is considerably reduced. This reduction is not dependent upon the ionic concentration and a 10-fold increase in Mg++ or Mn++ from the normal concentration of 10 mg ion/litre fails to increase the flocculation intensity. Low concentrations (1–10 mg ion/litre) of Na+ or K+ induce flocculation in those strains displaying intense flocculation with Ca++, but high concentrations of either Na+ or K+ (50–100 mg ion/litre) antagonize floc formation. It is suggested that divalent ions act by bridging cells through negative charges on the cell surface, whereas monovalent ions induce flocculation via a “counter ion” effect where the repellent forces of the negative charges on the cell surface are neutralized, thus allowing some floc formation due to hydrogen bonding or other types of non-ionic bonding between cells. The antagonism of high concentrations of monovalent ions towards flocculation may be due to the fact that all available cell surface charges are neutralized, resulting in insulation of the cells and thus preventing cell-to-cell hydrogen bonding.

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