HEAT RESISTANCE OF BACTERIA IN ALCOHOL-FREE BEER

Abstract

Two of the most heat resistant beer spoilage organisms found to date, Pediococcus acidilactici and Lactobacillus delbrueckii, and two human pathogens, Escherichia coli 0157:H7 and Salmonella typhimurium (both recently associated with outbreaks of diarrhea and hemolyticuremic syndromein apple cider), were tested for heat resistance in commercial alcohol-free beer and commercial 5% alcohol beer. Using the attemperated dilution blank adaption of the multiple point method, known cell concentrations were inoculated into 5% alcohol beer and alcohol-free beer held at a variety of heating temperatures. Survival curves, D values, phantomthermal death time curves, and Z values were determined. Decimal reduction times at 600C (D6o), a common temperature for beer pasteurization, were obtained by extrapolation. Pathogens demonstrated 3 to 17 times more heat resistance in alcohol-free beer and both lactic acid bacteria showed an increased resistance to heat of 4 to 7 fold in alcohol-free beer compared to 5% alcohol beer. Results illustrated a significant difference in the pasteurization parameters required to achieve microbiological stability of alcohol-free beers compared to 5% alcohol beer. Although pathogens tested are not at all heat resistant, and do not survive pasteurization temperatures even over short time intervals, these organisms can grow in alcohol-free beer and industry is cautioned about the safety and sale of unpasteurized low alcohol products when processed by filtration.