The impact of composition, environment and hygiene on the microbiome and spoilability of draught beer

Jevons, Alexander Lee (2022) The impact of composition, environment and hygiene on the microbiome and spoilability of draught beer. PhD thesis, University of Nottingham.

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Since the mid-1970s draught beer sales have been in decline. The on-trade has been impacted by changing consumer preferences, increased taxation, a competitive off-trade market and more recently the COVID-19 pandemic. Off-trade beer served in bottle/can is in the condition set by the brewer and will be ‘in-spec’. Comparatively beer served at the on-trade is subject to variable beer-line hygiene and therefore quality is variable from account to account. Assuring beer quality at the on-trade is vital to a brewer’s reputation and economic sustainability. But in light of changing dispense parameters and increased complexity, variable hygiene regimes and a declining market – there remain significant challenges ahead.

Draught beer microbiology has been a largely ignored area of research in the brewing industry since the early to mid-20th Century. Largely, our knowledge of draught beer spoilage microorganisms has been driven from historical works – with little to no work conducted on the microbiome of draught beer. Moreover, irrespective of the style of beer, beer spoilage microorganisms are presumed consistent irrespective of the distinct environmental differences between styles. Therefore, our primary work aimed to identify the ‘culturable’ microflora of draught beer across a range of styles. It was revealed in this work Brettanomyces sp. and Acetobacter sp. were ubiquitous spoilers of draught beer irrespective of style, and beer style did influence the microflora abundance. However, it was recognised in this work the culturable microbiome was not reflective of the true microbiome due to the phenomenon of ‘non-culturability’. This work was later repeated using Oxford Nanopore Technologies MinION Next-generation sequencing (NGS) tool. For the first time NGS was conducted on draught beer samples and revealed a number of new microorganisms from draught beer – but further demonstrated differences between beer styles and the impact of poor hygiene.

Biofilms in the brewing process are well-documented and although recognised in the on-trade are not discussed with equal importance. Biofilms can harbour numerous microorganisms and act as a source of fresh contamination after cleaning. Current cleaning practices at the on-trade do not utilise the four elements of ‘Sinner’s circle’ (mechanical action or temperature) and would be classed as an ineffective CiP regime in the brewing industry and elsewhere. This project aimed to firstly develop a method capable of replicating and quantifying biofilms in dispense systems, which was both affordable, reproducible, simple, and high throughput. After the development of this method, it was proceeded by initial work on introducing the missing elements of the ‘Sinner’s circle’, which was revealed to improve cleaning effectiveness using the assay.

Finally, it was noted throughout these works beers were spoiling at different rates despite being of the same style. In this work beers were subject to a range of analyses such as LC-MS for tracking tricarboxylic acids during forcing, high performance anion-exchange chromatography for fermentable quantification, free amino nitrogen (FAN), and pyruvic acid quantification. Moreover, the impact of supplementing a range of beers with sugars of varying complexity was analysed. This work revealed maltose to be a poorly used sugar irrespective of style or source inoculum, FAN and pyruvic acid to be potential spoilage indicators, and revealed beer spoilability began to assess the predictability of beers spoilability.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Quain, David
Powell, Chris
Keywords: draught beer, breewing technology, microbiology
Subjects: Q Science > QR Microbiology
T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 71548
Depositing User: Jevons, Alexander
Date Deposited: 17 Aug 2023 12:43
Last Modified: 17 Aug 2023 12:43

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