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