The safety of beef burgers is dependent on sufficient cooking to ensure the destruction of pathogens such as Shiga
toxin-producing Escherichia coli (STEC) O157. It is recommended that beef burgers are cooked to a minimum core
temperature of 70 °C for at least two minutes or to a core temperature of no less than 75 °C. However, in recent
years, catering establishments have started offering beef burgers prepared at temperatures below a core temperature
of 70 °C.
It is possible to achieve an ‘equivalent cook’ (equivalent to 70 °C for two minutes) at lower temperatures if the heat
is applied for longer times. However, calculating an ‘equivalent cook’ requires the use of a mathematical formula
that uses the z-values of the target organism, which is usually Listeria monocytogenes, as it is one of the most
thermal-resistant foodborne non-spore-forming bacterial pathogens. The z-value recommended for inactivation
of L. monocytogenes is 7.5 °C. In 2007, the UK Advisory Committee on Microbiological Safety of Food (ACMSF)
recommended using a z-value of 6.0 °C for calculating equivalent cooks when cooking burgers, based on heat
inactivation data for STEC O157. These two z-values give different cooking time requirements at a given target
temperature. Thus, the objective of this report was to determine which z-value was more appropriate (would offer
the greatest food safety protection)
