Beer metabolomics: molecular details of the brewing process and the differential effects of late and dry hopping on yeast purine metabolism

The flavour of beer is complex, based upon changes at the molecular level in the key raw materials, notably grain, hops and yeast, as well as during the process stages that comprise malting and brewing. As analytical techniques evolve in their sophistication and sensitivity, there are opportunities to delve ever more deeply into the fate of small molecules in brewing. To this end, 1H nuclear magnetic resonance (NMR) metabolomics was used to follow the progression of 76 metabolites in four different late or dry hopped beers (brewed in triplicate) at five time points throughout the brewing process. The majority of the metabolites identified, including sugars, amino acids and nucleotides, significantly decreased in concentration from the start of the boil to post-secondary fermentation, whereas energy-related and fatty acid associated metabolites significantly increased in concentration as wort nutrients were consumed by the yeast. Adenine was significantly higher in the dry hopped brews than in the late hopped brews after both primary (p=2.1×10-6) and secondary (p=2.7×10-9) fermentation, while 2′-deoxyadenosine (after primary, p=1.1×10-2, after secondary, p=3.2×10-5) and adenosine (after primary, p=2.6×10-8; after secondary, p=3.1×10-7)were significantly lower in the dry hopped beers at these time points. These results give molecular insight into the brewing process and the differential effects of hopping methods on yeast purine metabolism.