The growth and survival of food-borne pathogens in sweet and fermenting brewers' wort

Abstract

The aim of this study was to investigate the factors affecting the survival and growth of four food-borne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus) in sweet and fermenting brewery wort. The Gram-negative pathogens (E. coli and Salm. Typhimurium) were capable of growth during the initial stages of fermentation in hopped wort, although they were quickly inactivated when added during the later stages of fermentation. When the wort was left unpitched, the two Gram-negative pathogens grew unabated. Pathogen growth and survival was enhanced as the pH was increased, and as both the ethanol and original gravity were decreased. Although having no effect on the Gram-negative pathogens, low levels of hop iso-alpha-acids were sufficient to inhibit L. monocytogenes, and a synergistic antimicrobial effect between iso-alpha-acids and pH was observed. S. aureus failed to initiate growth in all of the test worts. There appears to be no reason for concern of the safety of a "typical" wort during fermentation, however due attention should be paid when wort is stored or antimicrobial hurdles are lowered, for example in the production of reduced and alcohol-free beer, and in unpasteurised products.