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RESEARCH PUBLICATIONS

DRAUGHT BEER HYGIENE: USE OF MICROPLATES TO ASSESS BIOFILM FORMATION, GROWTH AND REMOVAL

December 15th, 2020

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.

DRAUGHT BEER HYGIENE: A SURVEY OF ON-TRADE QUALITY

November 6th, 2018

The quality of draught beer in 57 on-trade licensed premises in 10 locations in the UK Midlands was assessed using a forcing test. Of 149 samples of standard lager (‘SL’, abv ≤ 4.2%), 44% were in the ‘excellent’ quality band compared with 16% of 88 samples of keg ale (‘KA’, abv ≤ 4.2%). Of the total of 237 samples, >90% were represented by two lager and two ale national brands. There were differences in the quality index (QI) between the brands, with lager SL3 having a QI of 84% compared with 72% for lager SL6, 71% for ale KA5 and 68% for ale KA1. The susceptibility of the four brands to spoilage was assessed using a challenge test with microorganisms taken from forced draught beer samples of the brands. Ale KA5 (challenge test QI = 87.5%) was the most resistant to spoilage followed by lager SL3 (81.3%), lager SL6 (75%) and ale KA1 (62.5%). Keg beers in accounts with a national cask beer quality accreditation had the same QI as those without accreditation. Analysis of price vs quality showed that the most expensive price band had the lowest quality. Draught beer quality declined as the number of dispense taps increased across the bar. It was also noted that dispense into branded half-pint glasses had variable take-up, with lager SL3 served in the correct branded glassware on 71% of occasions but only on 5% of occasions for lager SL6. None of the keg ales were served in correctly branded glassware.

DRAUGHT BEER HYGIENE: A FORCING TEST TO ASSESS QUALITY

October 9th, 2017

Draught beer quality can be compromised by the growth of spoilage microorganisms. Whilst best practice for assuring dispense hygiene is broadly recognized, it is not always fully or regularly implemented. In some markets, tap nozzles are removed and stored overnight at room temperature in carbonated (soda) water. The next morning they are returned (sometimes after rinsing) to the dispense tap. The effectiveness of this approach is compared with soaking in diluted line-cleaning solution (UK best practice) or a solution containing hypochlorous acid (commercial sanitizing tablets). Two novel approaches – ozonated water and use of ultrasonics – were also evaluated. Bioluminescence analysis of microbial attachment to the inner surfaces of nozzles showed that soaking in carbonated water resulted in gross contamination. Sanitizing tablets achieved ‘commercial sterility’ and a 4-log reduction in bioluminescence compared with carbonated water. The efficacy of hypochlorous acid was confirmed by incubating cleaned nozzles in fresh beer without any increase in turbidity. Diluted line-cleaning solution was less effective and achieved a 2-log reduction. Ultrasonics reduced microbial attachment but effectiveness was aligned to increasing process time. Soaking in ozonated water was without antimicrobial impact. This work has shown carbonated water to be ineffective in cleaning microbiologically contaminated nozzles. This is a concern as these microorganisms derive from the dispense line, the environment and likely human interaction. To minimize the risks of transfer to dispensed product or back-contaminating the dispense line, soaking draught beer nozzles in an effective sanitizing solution is strongly recommended.

DRAUGHT BEER HYGIENE: CLEANING OF DISPENSE TAP NOZZLES

May 15th, 2016

Draught beer quality can be compromised by the growth of spoilage microorganisms. Whilst best practice for assuring dispense hygiene is broadly recognized, it is not always fully or regularly implemented. In some markets, tap nozzles are removed and stored overnight at room temperature in carbonated (soda) water. The next morning they are returned (sometimes after rinsing) to the dispense tap. The effectiveness of this approach is compared with soaking in diluted line-cleaning solution (UK best practice) or a solution containing hypochlorous acid (commercial sanitizing tablets). Two novel approaches – ozonated water and use of ultrasonics – were also evaluated. Bioluminescence analysis of microbial attachment to the inner surfaces of nozzles showed that soaking in carbonated water resulted in gross contamination. Sanitizing tablets achieved ‘commercial sterility’ and a 4-log reduction in bioluminescence compared with carbonated water. The efficacy of hypochlorous acid was confirmed by incubating cleaned nozzles in fresh beer without any increase in turbidity. Diluted line-cleaning solution was less effective and achieved a 2-log reduction. Ultrasonics reduced microbial attachment but effectiveness was aligned to increasing process time. Soaking in ozonated water was without antimicrobial impact. This work has shown carbonated water to be ineffective in cleaning microbiologically contaminated nozzles. This is a concern as these microorganisms derive from the dispense line, the environment and likely human interaction. To minimize the risks of transfer to dispensed product or back-contaminating the dispense line, soaking draught beer nozzles in an effective sanitizing solution is strongly recommended.

ASSURING THE MICROBIOLOGICAL QUALITY OF DRAUGHT BEER

2015

D.E. Quain International Centre for Brewing Science, School of Biosciences, University of Nottingham, Loughborough, Leicestershire, UK

DRAUGHT BEER QUALITY - CHALLENGES AND OPPORTUNITIES

2007

In the majority of European markets, draught beer is in slow long-term decline. Whilst numerous factors – political, economic, social and technical – have been implicated, poor beer quality has played a significant role in consumer dissatisfaction with draught beer. The challenge to raise the quality bar is being met by innovation from cellar to tap. This paper describes the numerous developments that range from the consumer (mystery shopper accreditation) to technology led such as improved product cooling, glassware that aids presentation, dispense tubing that deters biofilm attachment, better and assured line cleaning and the opportunities from real time, remote data logging.

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