Heat Resistance of Bacteria in Alcohol-Free Beer

Abstract

Two of the most heat-resistant beer lactic acid bacterial spoilage organisms found to date, Pediococcus acidilactici and Lactobacillus delbrueckii, and two human pathogens, Escherichia coli O157:H7 and Salmonella typhimurium (both associated with recent apple cider outbreaks of diarrhea and hemolytic uremic syndrome), were tested for heat resistance in commercial alcohol-free (0.5%, v/v) beer and commercial 5% (v/v) alcohol beer. Using the attemperated dilution blank adaptation of the multiple-point method, known cell concentrations were inoculated into the two types of beer held at various heating temperatures. Survival curves, D values, and subsequently phantom thermal death time curves and Z values were determined. Decimal reduction times at 60°C (D60), a common temperature for beer pasteurization, were obtained by extrapolation. Both lactic acid bacteria showed a four- to sevenfold increase in resistance to heat in alcohol-free beer compared to 5% alcohol beer, and pathogens demonstrated as much as 3 to 17 times more heat resistance in alcohol-free beer. Results illustrated a significant difference in the timetemperature relationship 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, many of these organisms were found to grow in the alcohol-free beer tested (but not in normal beer), and therefore industry is cautioned about production of such alcoholfree products by filtration or as draught beer.