New concepts for rapid yeast settling. I. Flocculation with an inert powder

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Abstract
A novel technique for settling microorganisms was described. The technique involves adding a dense, inert powder to a suspension of microorganisms under conditions where flocculation of the microorganism with the inert powder occurs. The flocs formed are small and relatively dense and settle rapidly. Suspensions of S. cerevisiae yeast were flocculated with several different inert seed materials achieving rapid settling and separations of up to 99.9%. Ni powder was used as a seed material for most experiments and Fe sand showed promise as a cheaper seed for large-scale use. The degree of flocculation and cell separation obtained depended largely on the seed concentration and the components in solution. Temperature and pH had little effect. When the method was initially applied to a practical fermentation, flocculation was poor because of inhibiting compounds in the fermentation medium, but modification of the technique produced good flocculation in the medium.