M-25: A springboard to understanding beer flavor stability: The role of bound-state aldehydes

J. J. BAERT (1), J. De Clippeleer (1), L. De Cooman (1), G. Aerts (1); (1) KU Leuven, KAHO Sint-Lieven, Ghent, Belgium

Finishing and Stability
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Through extensive research over the past decades, a thorough understanding and improved control of colloidal, foam, color, and microbial stability of beer has been obtained. The chemistry of flavor instability, however, largely remains a mystery, although it is certain that aldehydes play a crucial role in the perception of “aged” flavors. Their concentration increase coincides with the appearance and increase in intensity of highly undesirable sensory attributes. Several pathways may lead to a variety of key sensorial aldehydes during beer production, but it remains unclear to what extent these reactions proceed after beer packaging. Previous research yielded strong indications that aldehydes, either derived from the raw materials or formed during beer production, are partly bound to other compounds, obscuring them from instrumental and sensorial detection. Since freshly bottled beer is not in chemical equilibrium, these bound aldehydes may be released over time, causing stale flavors. In this work, automated sample pre-treatment aimed at releasing bound-state aldehydes, using pH adjustment or the addition of competing compounds to shift equilibria. Subsequent quantification was performed using headspace solid-phase microextraction gas-chromatography mass-spectrometry with on-fiber derivatization. The formation of bound aldehydes was confirmed in model solutions. Moreover, one type of binding, not yet reported in a brewing context, was identified. Sample pre-treatment for aldehyde release before quantification was optimized. The obtained methodology was subsequently applied to complex samples to estimate their bound-state aldehyde content. Sample pH adjustment clearly yielded differential behavior between samples, and between aldehydes as well, indicating the complexity of the subject. The addition of competing compounds also shows very promising results, especially in regard to the newly identified bound-state type. Based on these procedures, flavor stability of beer may become more predictable through analysis of fresh samples. Moreover, this methodology may serve as a tool for selecting raw materials, and brewing parameters may be evaluated based on their influence on the bound-state aldehyde content in beer, which may potentially improve beer flavor stability greatly in the future. 

Jeroen Baert (born 1987) received a degree in bioscience engineering from the University of Ghent (Belgium) in 2010, with a specialization in cell and gene biotechnology. Chasing his love for the complexity and diversity of beer, he came in contact with the Laboratory of Enzyme, Fermentation and Brewing Technology (EFBT) of KAHO Sint-Lieven, which is renowned for its malting and brewing research, and was offered a position to work on a Ph.D. thesis on beer flavor stability. His project, focused on free and bound aldehydes in the chain from barley to aged beer, takes place in collaboration with the Bioscience Engineering Department of the University of Leuven (Belgium) and receives financial support from the Flemish government. In addition to his analytical work, he is a valued member of the sensory panel and performs GC-olfactometric characterizations on a regular basis.

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