EFFECT OF PHYSIOLOGICAL STRESS ON THE SURFACE-PROPERTIES OF BREWING YEASTS

Brewer's yeast may be stored before inoculation into a fermentation ve ssel, and during these periods of storage, starvation may occur. The e ffect of starvation on yeast inoculum condition and its subsequent fer mentation performance in brewing is important but not well understood. Although the physical properties of brewing yeast cell surfaces influ ence flocculation, they have not previously been used to ascertain the physiological state of brewing yeast. Starvation has been shown to in fluence the technological behavior of yeast. Indeed, starved yeast wer e observed to be less flocculant in beer. The characterization of the yeast cell surfaces involved the use of techniques such as dye retenti on, electrophoretic mobility, solvent partition, whole cell low-pressu re chromatography, and electron microscopy. Starved cells were signifi cantly less negatively charged compared with those that were non-starv ed, although surface hydrophobicity was largely unaffected. Modificati ons in cell surface topography and colony morphology also were observe d. It is suggested that the cell surface characteristics reflect some aspect of the physiological condition of brewing yeast.