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ASPECTS OF YEAST FLOCCULATION. SIZE DISTRIBUTION AND ZETA‐POTENTIAL
Author(s) -
Bowen W. Richard,
Ventham Timothy J.
Publication year - 1994
Publication title -
journal of the institute of brewing
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.523
H-Index - 51
eISSN - 2050-0416
pISSN - 0046-9750
DOI - 10.1002/j.2050-0416.1994.tb00817.x
Subject(s) - yeast , fermentation , flocculation , chemistry , zeta potential , sizing , food science , chromatography , chemical engineering , biochemistry , organic chemistry , nanoparticle , engineering
The technique of laser diffraction particle sizing has been used to directly measure the size distribution of the components of wort during fermentation. The work has been carried out for three yeasts, a bottom cropping ale yeast, a top cropping ale yeast and a lager yeast. Samples for sizing have been taken from the bottom and middle of the fermentation vessel at various times during the course of fermentation, with the results being reported as number distributions. It Is found that yeast sedimented to the bottom of the fermentation vessel is present either as single cells or as small cell aggregates with a characteristic dimension of about three times that of the single cells. This shows that flocculation is not necessary for sedimentation and that the basic units in stable aggregates are relatively small. The relative proportion of the sedimented cells in aggregated form increases as fermentation proceeds. The time dependence of the size distribution of materials remaining dispersed during fermentation is more complex. There is generally a bimodal distribution of single cells and small aggregates with variable amounts of sub‐micron trub which in some cases increases in importance as fermentation becomes more vigorous. The electrokinetic properties of the yeast cells and trub have been studied with the results reported as zeta‐potentials. It is found that toward the end of fermentation, and especially in the case of ales, there will be attractive electrostatic interactions between the yeast cells and the trub which would make a contribution in facilitating flocculation.