Effect of Aeration in Propagation on Surface Properties of Brewers’ Yeast

Abstract

Traditionally, brewers’ yeast is propagated through a series of poorly aerated batch fermentation vessels. Acknowledgement of the importance of yeast quality in brewery fermentation performance and the requirement of adequate oxygen to ensure yeast quality has prompted the investigation of alternative propagation schemes. Here, the effect of aeration on yeast production, surface properties and flocculation of 4 brewers’ yeast strains (3 flocculent, 1 non-flocculent) have been investigated. The biomass growth rates and yields of all strains were improved on aeration during the propagation stage, as expected. In addition, changes were observed in the hydrophobicity and surface charge of the cell. Aeration lowers the hydrophobicity and increases the total charge on the cells while also increasing the flocculation capacity of flocculent strains of yeast. This observation is contradictory to the prediction of the DLVO theory and suggests the dominance of the lectin mechanism over classical colloidal flocculation theory. The strain classified as ‘non-flocculent’, and measured to be very weakly flocculent, showed the reduced hydrophobicity and increased charge in the presence of aeration, however its flocculence decreased in accordance with DLVO theory. This is consistent with the ‘non-flocculent’ strain lacking a lectin mechanism of flocculation. Further studies are required to determine the effect of aeration on fermentation performance and the effect of altered surface properties and flocculence on brewery fermentation.