Draught beer hygiene: use of microplates to assess biofilm formation, growth and removal

Abstract

Draught beer quality is assured by the management of microbial biofilm in dispense lines through regular and effective line cleaning with alkaline detergent. Here, a method is described which enables biofilm formation, growth and removal to be assessed in 96 well polyvinyl chloride microplates. Draught beer (and cider) microflora formed reproducible biofilms in their ‘parent’ beer after incubation at 15°C for seven days. Biofilm formation by four draught beer styles – keg lager, ale, stout and cask ale ‐ was assessed and was enhanced by periodic replenishment with fresh beer. The rate of biofilm formation by microflora from keg beers decreased with increasing temperature whereas with cask ale it increased. Oxygen enhanced biofilm formation with microflora from cask ale but not keg. Simulation of line cleaning in microplates with a proprietary alkaline solution failed to kill all microflora and the microorganisms regrew in all four beer styles. Further, the line cleaning process was increasingly ineffective with older biofilms. It is suggested that the method reported here will help focus attention on the efficacy of line cleaning, in particular, the role of mechanical action, which contributes little to the standard manual line cleaning process in the UK. This and other investigations will hopefully contribute to the ultimate intention of improving and assuring draught beer quality.

The role of acetic acid bacteria in brewing and their detection in operation

“…While AAB are already pretty rare in beer production, they can be captured in draught beer in relatively high amounts. The problem of tap equipment together with beer lines is presence of oxygen and higher temperature in some parts of this system in combination with insufficient hygiene (Jevons and Quain, 2021). These cases have led to a repeatedly confirmed finding that some AAB strains are able to survive under limitation of oxygen Van Vuuren and Priest, 2003), in other words the traces of oxygen are enough to maintain viability.…”

The enhanced susceptibility of alcohol‐free and low alcohol beers to microbiological spoilage: implications for draught dispense

“…The beers and the licensed public houses ('accounts') used in this work are anonymised using codes to provide continuity with past studies (15)(16)(17). The beers used in this work were 'standard lager' (SL, ≤ 4.1% ABV), 'premium lager' (PL, > 4.1% ABV), 'keg ale' (KA, 3.6% ABV), stout (ST, 4.2% ABV), 'alcohol-free beer' (AFB < 0.05% ABV), 'low alcohol beer' (LAB < 1.2% ABV).…”

“…Studies on beer spoilage typically involve inoculation of a single species of microorganism (usually Lactobacillus) from culture collections or, originally, from beer (28,(38)(39)(40). However, draught beer spoilage reflects the growth of mixed microflora, of which some are ubiquitous (species of Brettanomyces, Acetobacter) while others are more specific to beer style (lactic acid bacteria in lager, Rhodotorula mucilaginosa in keg ale) (17). As the driver for this work is the dispense of draught AFB/LAB, it is more appropriate to use multi-species microflora from draught beer rather than pure, single species for challenge testing.…”

“…The ethanol sensitive Megasphaera has been noted as being a risk to low alcohol and (presumably) alcohol-free beers (33). Whilst an unpleasant microorganism in producing malodorous aromas (43), as an obligate anaerobe its likely environment would be in the anaerobic depths of biofilm in a draught beer line (17).…”

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

“…Although the best practice in the UK for line cleaning is carried out weekly, many accounts clean every 2 or 3 weeks. The cleaning process is essentially static and lacks mechanical action to clean effectively (Jevons & Quain, 2021). Accordingly, line cleaning as practiced in most public houses is only partly successful in removing microflora and the lines quickly recontaminate.…”