Control of Fermentation By-Products and Aroma Features of Beer Produced with Scottish Ale Yeast by Variation of Fermentation Temperature and Wort Aeration Rate

ABSTRACT

Fermentation and pitching conditions provide numerous opportunities for the control of the beer's final sensory characteristics. The fermentation temperature and wort aeration rate relate significantly to the formation of many flavor-relevant substances, in particular esters, acids, and higher alcohols. A commercially available ale yeast was selected for fermentation trials investigating fermentation temperature and dissolved oxygen effects. Both parameters were varied in accordance with a central composite design. All obtained data were used for the development of a predictive model for the by-product control in dependence of pitching and fermentation conditions, using regression analysis, principal component analysis (PCA), and hierarchical cluster analysis (HCA). It was shown that the selection of certain technological parameters, in particular fermentation temperatures, enhanced specific flavor characteristics such as fruitiness and acidity. Higher fermentation temperatures promoted the formation of many aroma relevant substances, which were clustered in relation to technological parameters and the final flavor perception. Samples fermented at 20°C achieved the highest sensory preference. In addition, specific substances (e.g., acetaldehyde and alcohols) in the final beer correlated with integrals of the cell density curves in dependence of the fermentation time. Fermentation phases in which substances varied corresponding to yeast cell state were detected.

KEYWORDS:

• Ale
• fermentation
• flavor
• pitching
• sensory
• yeast

Acknowledgments

The authors acknowledge the contribution of the central laboratory staff of Brau Union Österreich AG for chemical wort and beer analyses. Our special thanks also go to the team of the breweries Schwechat and Kaltenhausen for their participation at the tastings (Brau Union Österreich AG). The authors declare that there is no conflict of interest or any competing financial interests.