Study of the impact of the yeast pitching rate on the fermentation kinetics and the organoleptic qualities of the Zinnebir beer

Details

Supervisors

Collin, Sonia

Faculty

Faculté des bioingénieurs

Degree label

Master de spécialisation en génie brassicole

Abstract

In the interest of learning more about its production and achieving a consistency of its finished products, the aim of the present work was to study the impact of the wort pitching rate on the fermentation kinetics and the organoleptic qualities of the finished beer at an industrial scale at Brasserie de la Senne. For this purpose, the study focused on the influence of two different pitching rates – 2 and 6 million viable cells/mL – on a single beer of the brewery, the Zinnebir. As Brasserie de la Senne propagates its own yeast, the target pitching rates were first inoculated from the propagator following yeast cells counts and viability measurements. Then, the influence of the pitching rate on the fermentation kinetics was studied through fermentation monitoring and its influence on the organoleptic properties of the finished beer was studied through the quantitation by gas chromatography of aromatic by- products and the sensory analysis of the finished beers with a panel of trained and untrained tasters First, the study conducted on the fermentation kinetics showed that a higher pitching rate resulted in shorter fermentations with slightly better attenuation. However, the two pitching rates of 2 and 6 million viable cells/mL were appropriate to perform successful fermentations in the time stated by the brewery. Secondly, the study conducted on the quantitation of volatiles produced during the beer fermentation showed that, despite some variation, the concentrations of volatiles of all beers were very low compared to those found in typical ale beers, and the calculated higher alcohol to ester ratios were as low as those found in lager beers. In the sensory analysis, no differences in the organoleptic properties of the finished beers were detected by a panel of trained and untrained tasters, representative of a typical consumer. In conclusion, the interpretation of the results obtained in this study suggests that it would be preferable for Brasserie de la Senne to use a pitching rate of 2 million viable cells/mL for the fermentation of its Zinnebir beers, as this inoculum size does not differ as much from the pitching rate of 6 million viable cells/mL in terms of fermentation kinetics and organoleptic qualities of the finished beer, but allows for a better reproducibility of the fermentations and volatile concentrations obtained in the final beer.