Martin Zarnkow (1), Mathias Hutzler (1), Fritz Jacob (1), Maximilian Michel (1); (1) Research Center Weihenstephan for Brewing and Food quality, Technische Universität München, Freising, Germany

Yeast, Fermentation, and Microbiology

The brewing sector is ruled by Saccharomyces species. Besides spontaneous fermentation there is very little use of non-Saccharomyces yeasts all around the beer industry. There are approximately 670,000 species of yeasts in different habitats, of which only 20 species are being used for industrial needs. The possibility of a lot of new aroma compounds produced by this huge variety of yeasts is unimaginable. To make use of this big field of unknown species, aromas and maybe new aspects of taste or functionalities for more mouthfeel or higher pressure resistant yeasts, a screening system is being developed. The screening system includes preliminary biochemical tests to make sure the investigated yeasts can survive in beer wort and of course ferment it. This includes the carbohydrate fermentation of wort sugars, hop resistance, ethanol resistance, and different combinations. It is continuous with the propagation ability and flocculation behavior as well as different brewing trials with the observation of all important beer characteristics. It also includes precursor tests for phenolic off-flavors by sensory evaluations. First trials were done with 12 different Torulaspora delbrueckii strains from various habitats like fruits, infected beer samples, wine and cheese industry. This species has already been used in the wine industry for more fruitiness in certain wines. There has also been very little effort to produce beer. The tests and trials show large differences in just one species when it came to sugar fermentation and ethanol formation, as well as flavors. The flavor varies from honey-like to pear- or apple-like fresh fruitiness. The brewing ability seems to be present. One strain was found to be suitable for the production of a beer with an average ethanol concentration of about 5 vol/vol% and unique flavor of currant, honey and tropical fruits. The fermentation was optimized by a response surface method changing wort pH value, fermentation temperature and pitching rate. More yeast strains are being looked at from different spontaneous fermented beverages around the world, as well as spoilage yeasts. The screening system is being updated constantly to improve the finding of new yeasts for the brewing industry.

Martin Zarnkow apprenticed as a brewer and maltster from 1989-1991 at a small brewery in Frankonia. Martin completed a Dipl.-Ing. (FH) graduate degree with an option in brewing technology in 1996 at the TU München Weihenstephan. Martin worked as a brewmaster for one year in a medium-sized brewery in Germany. Since 1997 he has been at TU München. Martin is the head of research and development at the Research Institute Weihenstephan for Brewing and Food Quality. In 2010 he finished his external Ph.D. research at the University College of Cork, Ireland, on the subject “Proso Millet (Panicum miliaceum L.) a Sustainable Raw Material for the Malting and Brewing Process.”