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Resurrection of the lager strain Saccharomyces pastorianus TUM 35
M. Hutzler, L. Narzi, D. Stretz, K. Haslbeck, T. Meier-Drnberg, H. Walter, M. Schfer, T. Zollo, F. Jacob and M. Michel

Saccharomyces pastorianus lager yeast strains are some of the most important industrially used microbes used in fermentations. Lager beer types dominate the market with over 90 % of the market share. Although some popular and widespread lager strains, such as the most used strain Saccharomyces pastorianus TUM 34/70, are well characterized, little or nothing is known about old and seldom used lager strains from long-standing strain collections. Only two Saccharomyces pastorianus lager strain subgroups are known to date, Frohberg and Saaz. Most industrial, modern, high-performance lager strains belong to the Frohberg group. In this study our group reactivated a freeze-dried stock of a yeast culture (carrier matrix unknown, probably dry milk powder) of the historic strain TUM 35. The strain was presumed to have been lost over time. Fortunately, the freeze-dried stock was found in a forgotten box in a storage room (together with other historic strains) at the Research Center Weihenstephan for Brewing and Food Quality. TUM 35 grew after two weeks of applying a tailored reactivation protocol in liquid wort. This paper presents research on the history of the strain TUM 35. Its journey could be traced back from Freising-Weihenstephan to Nuremberg and to its origin Coburg in upper Franconia. Its history also revealed why this formerly very successful old yeast strain disappeared completely in the mid to late 1950s. We also confirmed the species using specific qPCR systems with marker DNA-regions for S. pastorianus identification. PCR-capillary electrophoresis of the IGS2-314 rDNA fragment showed the close relation to the strain TUM 34/70 but also the subtle differences in the DNA-fingerprint pattern. Phenotypic experiments and beer fermentation trials at volumes of 30 L could prove that TUM 35 performed like a typical Frohberg-type lager strain. It produced a straight, neutral and soft aroma profile in the final beer with a high degree of fermentation. Results of fermentation by-product analysis and other main beer parameters of the beer produced with TUM 35 lie within the specifi cations and reference values for Frohberg-type lager beers. In contrast to most other lager beer strains, TUM 35 produced no sulfuric aromas that could be sensed by the tasting panel in the final beer. This study is a first approach to improve the understanding of old lager beer yeast strains and also opens up opportunities for breweries to use forgotten old strains for standard or historic lager beer production.

Descriptors: yeast, Saccharomyces pastorianus, TUM 35, lager beer, fermentation, history, identification, differentiation

BrewingScience, 72 (March/April 2019), pp. 69-77