Brewers’ yeast, Saccharomyces cerevisiae, is divided into two basic groups: bottom-fermenting and top-fermenting yeast. The bottom-fermenting yeast flocculates during fermentation and sediments on the bottom of a fermentation tank where it forms a more or less stable layer. The flocculation ability is hereditary depending on the yeast strain and it may be lost. The reasons and mechanism of flocculation are not fully known; nonetheless, it is certain that the flocculation ability in the yeast is coded by at least eleven genes. Yeast flocculation is classified according to NewFlo and Flo 1 phenotypes. The presence of this feature is influenced by such factors as temperature of the environment, acidity, pressure, calcium ions, and contents of carbohydrates in the wort.

The aim of the work is to assess the influence of different carbohydrates on the flocculation ability of industrial brewers’ yeast Saccharomyces cerevisiae, and then to analyse genetic differentiation of the feature being examined.

The top-fermenting and bottom-fermenting strains of the brewers’ yeast Saccharomyces cerevisiae were chosen for tests. The yeast strains were cultured on a media containing different carbon sources: glucose, maltose, fructose, ethanol and peptone at different concentrations. The flocculation ability was measured spectrophotometrically at a wavelength of 600 nm. Genetic differentiation will be tested with the MSSCP method and if differences regarding migration of the analysed fragments of the FLO genes in the polyacrylamide gel are found, the sequential analysis will be performed.

During tests the flocculation ability of a typical industrial strain KKP 192 was confirmed. The degree of flocculation was stimulated, above all, by the presence of maltose and alcohol in a culture medium.

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