Process hygiene control in beer production and dispensing: Dissertation

Process hygiene plays a major role in the production of high quality beer.Knowledge of microorganisms found in the brewery environment and the control of microbial fouling are both essential in the prevention of microbial spoilage of beer.The present study examined the growth of surface-attached beer spoilage organisms and the detection and elimination of microbial biofilms.Moreover, the detection and characterisation of Lactobacillus lindneri, a fastidious contaminant, was studied. Beer spoilage microorganisms, such as lactic acid and acetic acid bacteria, enterobacteria and yeasts were shown to produce biofilm on process surface materials in conditions resembling those of the brewing process.However, attachment and biofilm formation were highly strain dependent.In addition, the substrates present in the growth environment had an important role in biofilm formation. Different surface materials used in the brewing process differed in their susceptibility to biofilm formation.PTFE (polytetrafluoroethylene), NBR (nitrile butyl rubber) and Viton were less susceptible to biofilm formation than stainless steel or EPDM (ethylene propylene diene monomer rubber).However, the susceptibility varied depending on the bacteria and the conditions used in the in vitro studies.Physical deterioration resulting in reduced cleanability was observed on the gasket materials with increasing age.DEAE (diethylaminoethyl) cellulose, one of the carrier materials used in immobilized yeast reactors for secondary fermentation, promoted faster attachment and growth of con-taminating L. lindneri than ceramic glass beads.Beer dispensing systems in pubs and restaurants were found to be prone to biofouling, resulting eventually in microbial contamination of draught beer and cleanability problems of the dispensing equipment.Detection of surface-attached microorganisms is crucial in process hygiene control.In situ methods such as epifluorescence microscopy, impedimetry and direct ATP (adenosine triphosphate) analysis were the most reliable when studying surface-attached growth of beer spoilage microbes.However, further improvement of these techniques is needed before they can be applied for routine hygiene assessment.At present hygiene assessment is still dependent on detachment of microorganisms and soil prior to analysis.Surface-active agents and/or ultrasonication improved the detachment of microorganisms from surfaces in the sampling stage.The ATP bioluminescence technique showed good agreement with the plate count method in the control of working dispensing installations.Hygiene monitoring kits based on protein detection were less sensitive than the ATP method in the detection of wort or surface-attached microorganisms. Effective process control should also be able to detect and trace fastidious spoilage organisms.In this study, the detection of L. lindneri was notably improved by choosing suitable cultivation conditions.L. lindneri isolates, which could not be correctly identified by API 50 CHL, were identified to the species level by automated ribotyping and by SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) when compared with well-known reference strains.SDS-PAGE was also able to discriminate between different strains, which is a useful feature in the tracing of contamination sources.