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Genetic and Phenotypic Characterization of Different Top-fermenting Saccharomyces cerevisiae Ale Yeast Isolates
Meier-Drnberg, T., Michel, M., Wagner, R. S., Jacob, F. and Hutzler, M.

Brewing yeast plays a pivotal role in determining the flavor and quality of beer. Different process techniques and fermentation conditions can interact with each yeast strain to create a wide variety of different flavor profiles. The craft beer movement encourages brewers to use more and more aroma-intense ale strains to create special, innovative beers. Breweries either maintain individual brewing strains or they order yeast strains from yeast strain providers or culture collections. To ensure a reliable level of quality and product stability it is necessary to genetically classify the strains involved. The origin of a strain is often unclear, and genetic drift or population drift over time cannot be excluded. Some isolates represent very close strains or the same strain. Whether two yeast strains are the same, similar or different, this does not provide any information on their phenotypic (brewing) properties. To determine these properties, genetic and phenotypic characterization methods were used, which distinguished brewing yeasts and determined their suitability and application potential for brewing. The five yeast strains Saccharomyces cerevisiae TUM 210, 211, 213, 506, 511 were characterized using a broad spectrum of genetic and phenotypic methods with a focus on brewing properties and sensorial performance. Sequencing ribosomal genes and spacer regions revealed that the strains belong to Saccharomyces cerevisiae and showed some polymorphisms. DNA fingerprinting techniques demonstrated that all strains were genetically different. Phenotypic characterization revealed that the brewing properties (e.g. fermentation performance, sugar utilization, amino acid utilization, cell growth, flocculation behavior, change in pH value, phenolic off-flavor, fermentation by-products, sulfur dioxide) and the sensorial characteristics of each strain were unique. The developed yeast characterization platform using special 2 l fermentation vessels is a broadly based, standardized tool to find the right yeast strain for distinct brewing aims.

Descriptors: saccharomyces cerevisiae, brewing yeasts, ale yeast, top-fermenting yeast strains, yeast haracterization

BrewingScience, 70 (January/February 2017), pp. 9-25