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Characterization of Different Bottom Fermenting Saccharomyces pastorianus Brewing Yeast Strains
K. Müller-Auffermann, A. Caldera, F. Jacob and M. Hutzler

Brewing yeast plays a pivotal role in determining the flavor and quality of beer. Therefore, it is crucial that reliable and practical information be obtained regarding the characteristics of individual strains. This paper presents a comparison of six commercially available bottom fermenting yeast strains. TUM 34/70 served as the standard against which these yeast strains were compared, since it is the most widely used bottom fermenting yeast strain in the world and is also the most comprehensively described scientifically. A fermentation plant consisting of 27 fermentors was developed and tested with this goal in mind. This plant was designed to allow fermentation to be controlled according to a set of variables which included temperature, aeration, cell count and pressure. For the purpose of carrying out fermentation trials, these fermentors provide conditions comparable to those found in large industrial tanks.In three separate sets of trials, the following attributes were measured at regular intervals during fermentation and after lagering: the drop in specific gravity and in pH, CO2 production, FAN reduction, residual maltotriose content, total yeast cell count, the number of cells in suspension, the surface charge of the cells, turbidity, sedimentation and the foam stability of the unfiltered beer, as well as the formation and degradation of vicinal diketones, fusel alcohols, esters, aldehydes and SO2. Finally, a proper organoleptic description comparing the unfiltered products was performed after lagering.In doing so, the strains were tested under conditions as close as possible to those present in actual brewing operations and thereby exhibited, in part, significant differences in their behavior. Moreover, new insights have been gained which had yet to be fully described scientifically. These include the change in the surface charge on the yeast cells and the absorption rate of certain amino acids during fermentation, which occur

Descriptors: yeast, brewing yeasts, Saccharomyces pastorianus, bottom fermenting yeast strains, lager, yeast characteristics, characteterization, TUM 34/70, TUM 34/78, TUM 193, TUM 194, TUM 66/70, TUM 44, TUM 69

BrewingScience - Monatsschrift für Brauwissenschaft, 68 (March/April 2015), pp. 46-57