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Abstract

Nowadays the interest in using non-Saccharomyces yeast to ferment beer has been increased. Different yeast strains can produce beer with a unique and very complex aroma and flavour profile. Using non-conventional yeast gives brewers an unparalleled selling point to differentiate themselves. Studies have been made to find non-Saccharomyces yeast strains that are able to complete the fermentation in pure or mixed cultures with Saccharomyces cerevisiae in order to produce a normal gravity beer with desirable aroma features. In this experiment mixed cultures of Metshnikowia pulcherrima in addition with Saccharomyces cerevisiae were evaluated for a Pale Ale beer production. In particular mixed cultures of Metshnikowia pulcherrima with the conventional yeast, in proportions 1:1 and 1:10, were used to ferment beer wort in an average temperatures of 20 °C and 13 °C. In addition to the fermentation time, the concentration of remaining sugars, the change in pH, the rate of consumption of available ammonia nitrogen and the ethanol content, we detected the aromatic compounds of each beer. In order to study the aroma profile of the beers, samples were taken one week after bottling, and one month into aging. Moreover beers were characterized by a distinctive overall analytical and aromatic profile. Indeed, the non conventional yeast was found to be capable of producing aromatic components such as higher alcohols and esters wich form a fruity and floral aromatic profile. Fermentation of Metshnikowia pulcherrima pure culture was also performed at two temperatures (13 ° C and 20 ° C) in order to compare the results of fermentation time, concentration of remaining sugars, consumption rate of available ammonium content, available ammonia content and most imprortantly the aromatic compounds produced during the first week after bottling.