Identification of spoilage microflora in draught beer using culture-dependent methods

Abstract

Aims: To determine whether the culture-dependent spoilage microflora found in draught beer are influenced by beer style.Methods and Results: Four beer styles-lager, ale, stout and cask ale -were sampled twice from five different public houses (accounts) in four different locations.The microbiological quality of the dispensed beers was determined by a culturedependent method ('forcing'), measuring the increase in turbidity after incubation at 30°C. The quality of draught beer varied from 'excellent' to 'poor' with cask beer samples having a higher Quality Index (90%) with keg ale the lowest (67.5%). With PCR amplified DNA (ITS1, ITS4, 16S rRNA primers) and blast identification of microflora, 386 colonies from agar plates were identified with 28 different microorganisms from five genera of yeast and six of bacteria. Seven micro-organisms were found in all beer styles with Brettanomyces bruxellensis, B. anomalus and Acetobacter fabarum representing 53% of the identified micro-organisms. A subsequent, limited study using PALL multiplex PCR GeneDisc technology on forced samples (without selection on plates) suggests that draught beer microflora is qualitatively broader. It is noteworthy that the microflora of spoilt draught beer resembles that involved in the production of Belgian Lambic sour beers.Conclusions: Draught beer was of variable quality. Culture-dependent analysis suggests that species of Brettanomyces and Acetobacter are core microflora with some micro-organisms being associated with beer style. Significance and Impact of the Study:The microbiological quality of draught beer is important both commercially and to the consumer. Here, we report the core and diverse microflora found in different styles of draught beer using culture-dependent methods. K E Y W O R D S beer spoilage, beer styles, draught beer, identification, microflora | 3729 MICROFLORA OF DRAUGHT BEER How to cite this article: Jevons, A.L. & Quain, D.E. (2022) Identification of spoilage microflora in draught beer using culture-dependent methods.

The two faces of microorganisms in traditional brewing and the implications for no- and low-alcohol beers

“…AAB do however remain problematic at the point of sale and can frequently be isolated from dispense systems in pubs and public houses, due to the presence of oxygen and elevated temperatures encountered ( Storgards, 2000 ). For similar reasons, regular occurrences of beer spoilage in draught beer kegs have been described, and AAB are still common in cask-conditioned and barrel-aged beers; 46% of the microflora isolated from cask ale samples were identified as acetic acid bacteria in a recent study by Jevons and Quain (2022) .…”

Estudio de la microbiota de cerveza artesanal producida a pequeña escala

“…En las cervezas artesanas es más probable que podamos encontrar alguna contaminación, que puede provenir tanto de levaduras como de bacterias que son capaces de crecer incluso en los ambientes típicos de estas cervezas, que, a su vez, disminuyen el crecimiento de algunas bacterias y levaduras por su bajo pH, alto contenido de dióxido de carbono o por tener pocos nutrientes. Esta posible contaminación puede alterar la cerveza, por ejemplo, enturbiándola y formándose sedimento (Jevons et al, 2022;Latorre et al, 2022). Las cervezas artesanales, por lo general, son más propensas al deterioro y la contaminación.…”