Yeast Physiological State Influence on Beer Turbidity
¹Saint-Petersburg State University of Information Technologies,Mechanics and Optics (ITMO University) Kronversky pr., 49, St Petersburg, 197101, Russia
²Baltika Breweries - Part of Carlsberg Group, 6 Verkhny per., 3, St Petersburg, 194292, Russia
Abstract:
The physiological state of yeast affects the intensity of propagation and biosynthesis of secondary metabolites and determines the sensory profile of beer. Besides that, yeast with low physiological activity increases the number of colloidal particles in beer, which consist of proteins and polysaccharides. The purpose of this study was to select a method for assessing the physiological state of yeast and to study the influence of yeast physiological state on the adsorption of compounds that determine the colloidal stability of beer. As a result of comparative analysis of different methods for determining the non-viable and weakened cells with dyes a certain correlation between them was found. The highest correlation (R2 = 0.84) was set between parameters obtained by staining yeast cells by methylene blue with Safranin O, which stains both dead and weakened cells and dihydrorhodamine 123, which detects only physiologically least active yeast. Sufficiently high correlation (R2 = 0.83) was observed when cells were stained with methylene blue, which identifies only dead cells, and with methylene blue with Safranin O. The worse the physiological condition of yeast, the less they adsorb turbidity-inducing compounds, so more substances remain in beer, reducing its stability. Thus, the increase in the proportion of damaged and non-viable cells from 24.2 to 32.2% leads to increased beer turbidity from 1.5 to 3.3%. Z-potential of yeast cell walls determines their sorption properties. Physiologically active yeast cells are able to adsorb positively charged colloids due to the negative charge of their surface. Activation of the yeast’s surface potential occurs in the presence of oxygen.