Maximilian Michel
Research Center Weihenstephan for Brewing and Food Quality, TU München, Niemcy

MIKROBIOLOGIA
Słowa kluczowe: new Yeasts, non-Saccharomyces, Torulaspora delbrueckii

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 where of 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 was 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 as well as different combinations. It continues 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 performed 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 v/v% 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. A brewery will start using the new strain in summer for a special summer beer. 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.