Dimethyl sulfide (DMS) is a substantial contributor to the aroma of many lager-style beers. Opinion varies on its desirability. It can be derived in beer from two sources: the thermal decomposition of S-methylmethionine (SMM) produced in the embryo of barley during germination, or the reduction of dimethyl sulfoxide (DMSO, derived from the breakdown of SMM during the curing of malt) by yeast. The enzyme that effects DMSO reduction is a reductase whose primary function is the reduction of methionine sulfoxide and which competes for reducing power with several other cellular systems. Control of DMS production from SMM is achieved by specifying precursor levels in malt, by attending to the vigor and duration of the boil, and by controlling the length of the whirlpool stand. Control of DMS production from yeast is achieved by specifying yeast strain, wort gravity, free amino nitrogen and pH, the type of fermenter (ergo the extent of volatilization), and the fermentation temperature.

The paper reviews a career of more than forty years researching topics in malting and brewing science. Some themes attracted particularly close attention, namely the endosperm cell walls of barley, dimethyl sulphide, flavour stability, foam and the impact of beer on health. However, the scope has been far broader than that. The underlying imperative was to pursue research that was close to application and always focussed on a specific need in the processes involved in the production of beer. © 2020 The Institute of Brewing & Distilling.

Although there are product-to-product differences, the majority of the crystal and caramel malts tested have been shown to have a net destabilizing impact on foam. A foaming test using a model beer has been developed to quantify the magnitude of this inhibitory effect. Lipid analysis using thin-layer chromatography reveals that there are elevated levels of triglycerides in problematic malts. There also appear to be oxidized lipids in the specialty malts, probably produced in the heating stage of malt production with higher levels in more intensely heated products. However some specialty malts, such as black malt, while containing such foam-negative entities, do display superior foaming properties, probably because they develop even more powerful foam-positive components in the severe heating events. © 2014 The Institute of Brewing & Distilling.

Dimethyl sulphoxide (DMSO) reductase is present in all brewing yeast strains tested, but is more readily detectable using activity stains on polyacrylamide gels than through direct spectrophotometric assay of crude extracts. The enzyme is detectable at higher activities in yeast cultivated at lower temperatures and this is because of increased expression of the primary gene that codes for the enzyme in yeast, MXR1. DMSO somewhat increases enzyme expression, notably in lager yeast by up to 70%, whereas methionine suppresses it. Both ale and lager strains produce enzymes of ~100,000 in molecular weight, but ion exchange chromatography divides the activity for both ale and lager yeasts into two fractions with distinct properties (heat tolerance, pH optimum, kinetic parameters). Copyright © 2017 The Institute of Brewing & Distilling.

Like iron and copper, manganese promotes the staling of beer, by converting ground state oxygen to reactive oxygen species. Manganese was detected in beers at levels that are likely to impact the aging of beer. Manganese originates in the grist materials but is present at even higher levels in hops. Although there is substantially more iron in those hops than manganese, the delivery into beer of these ions is much greater for manganese. Leaching of manganese into beer is much higher than in the equivalent quantity of deionized water. This study suggests that further study is warranted into the adverse impact of dry hopping on the flavor stability of beers.

American coolship ale (ACA) is a type of spontaneously fermented beer that employs production methods similar to traditional Belgian lambic. In spite of its growing popularity in the American craft-brewing sector, the fermentation microbiology of ACA has not been previously described, and thus the interface between production methodology and microbial community structure is unexplored. Using terminal restriction fragment length polymorphism (TRFLP), barcoded amplicon sequencing (BAS), quantitative PCR (qPCR) and culture-dependent analysis, ACA fermentations were shown to follow a consistent fermentation progression, initially dominated by Enterobacteriaceae and a range of oxidative yeasts in the first month, then ceding to Saccharomyces spp. and Lactobacillales for the following year. After one year of fermentation, Brettanomyces bruxellensis was the dominant yeast population (occasionally accompanied by minor populations of Candida spp., Pichia spp., and other yeasts) and Lactobacillales remained dominant, though various aerobic bacteria became more prevalent. This work demonstrates that ACA exhibits a conserved core microbial succession in absence of inoculation, supporting the role of a resident brewhouse microbiota. These findings establish this core microbial profile of spontaneous beer fermentations as a target for production control points and quality standards for these beers.

Ascorbic acid oxidase (AAO) develops in the embryo tissues of barley during steeping and initial stages of germination. Two AAO enzymes have been identified. One of them is of remarkably low molecular weight (<10,000). Both are very heat tolerant and capable of acting over a broad pH range. Both enzymes would be expected to function during conversion temperatures of mashing. Indeed, addition of ascorbic acid to mashes results in the survival of higher levels of polyphenol and thiols into wort and a reduced color in that wort, commensurate with AAO preferentially consuming oxygen which, thus, is less readily available for other reactions in mashes, including thiol oxidation and polyphenol oxidation. © 2014 American Society of Brewing Chemists, Inc.

NMR-focused metabolomic analysis has been employed to ascertain the extent to which a diversity of non-volatile substances change in level during maturation and storage on a pilot and commercial scale. No substantive changes were observed, leading to the conclusion that, once materials such as vicinal diketones and acetaldehyde have been dealt with, there is no merit in the prolonged storage of beer. © 2019 The Institute of Brewing & Distilling.

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.