Metabolomics of Unhopped Wort and Beer

Beer is the second most consumed beverage in the world. The beer market has changed
drastically in the last decades, especially with the rise of small-scale craft breweries, driven by the
enthusiasm to experiment with unique and new recipes and cater to a market that appreciates
artisanal products. Consumers’ desire for more complex flavour profiles demands a better
understanding of molecular explanations of how flavour arises in beer. The biochemical composition
of beer is complex, comprising hundreds of compounds from different chemical classes arising by
various mechanisms. There are a wide range of analytical approaches that can be implemented to
study beer’s composition and with the rise of highly sensitive extraction, separation, and detection
methods, coupled to multivariate analysis models, emergent properties of beer can be revealed.
The aim of this PhD thesis is to design a brewing process based on modern brewing practices,
take samples at various stages of the process, and then to analyse these samples using various mass
spectrometry-based methods and a metabolomics workflow. Key compounds discriminant to each
brewing stage were putatively identified, discussed, and compared between the methods; the
methods themselves and the workflow implemented was critically assessed, along with their
limitations and relative merits. The UPLC-MS approach results showed the most discriminatory power
within sample classes, and a larger diversity of chemical classes was putatively identified from its
results. A lack of food-related metabolomic platforms in the databases available makes the deeper
analysis of these results still a challenge.
Compounds derived from phenolic amino acids (phenylalanine and tyrosine) show promise as
precursors of flavour-active compounds. The phenylpropanoid pathway that is ubiquitous in plants
and the phenyl-glycosides found attached to malt’s husk could be sources of interesting flavour-active
compounds that may be released and transformed during the brewing process.