Effect of Physiological Stress on the Surface Properties of Brewing Yeasts

Brewer's yeast may be stored before inoculation into a fermentation vessel, and during these periods of storage, starvation may occur. The effect of starvation on yeast inoculum condition and its subsequent fermentation performance in brewing is important but not well understood. Although the physical properties of brewing yeast cell surfaces influence flocculation, they have not previously been used to ascertain the physiological state of brewing yeast. Starvation has been shown to influence the technological behavior of yeast. Indeed, starved yeast were observed to be less flocculant in beer. The characterization of the yeast cell surfaces involved the use of techniques such as dye retention, electrophoretic mobility, solvent partition, whole cell low-pressure chromatography, and electron microscopy. Starved cells were significantly less negatively charged compared with those that were non-starved, although surface hydrophobicity was largely unaffected. Modifications in cell surface topography and colony morphology also were observed. It is suggested that the cell surface characteristics reflect some aspect of the physiological condition of brewing yeast.