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.