Safe beef carcase export chilling procedures

Summary

The Meat Research Corporation baseline study of the microbiological quality of Australian meat, found problems with weekend chilling. These were attributed, mainly, to elevated holding temperatures. From the study, CSIRO recommended that the holding temperatures over weekends be no higher than 7°C.

Although 7°C is tolerated in some boning rooms, it is too cold for many because the hard fat produced gives rise to industrial problems especially with grain-fed cattle. Therefore many plants hold carcases at 10·C, the highest temperature allowable under the Export Meat Orders.

For many of the pathogens, the temperature region 7-lOºC is approaching the minimum temperature for growth and even a slight drop in temperature has a very significant effect on their growth rate and on whether or not growth even occurs.

In addition, the surface drying that occurs during chilling means that moisture is less freely available to bacteria. This reduced moisture availability is also inhibitory to bacteria.

The control of beef chillers in most export meat plants is such that different temperatures and fan speeds can be set for different stages of the overnight and weekend chilling cycles. Chilling cycles typically consist of a loading phase, chilling phase and a holding phase.

Most plants broadly follow recommendations contained in the CSIRO handbook 'Production of Chilled Meat for Export'.

These suggested a chilling phase with an air-on evaporator coil temperature close to O°C followed by a holding phase that maintains the carcase surface temperature no higher than 8ºC. However both the chilling temperature and holding temperature are often compromised to an extent in order to produce carcases with fat hardness that does not lead to industrial dispute or workers compensation or safety problems during boning.

Holding temperatures up to the allowable temperature of 10ºC do not lead to excessive bacterial growth during overnight chilling due to the short time periods involved. However during weekends, particularly long weekends, the holding period at 10ºC can exceed 60 hours. The main focus of this project has therefore been to evaluate industrially acceptable chilling cycles that adequately control growth of pathogenic organisms.

Investigations centred on the effect of closely controlling temperature and surface dryness (measured as water activity, aw which numerically is directly related to the relative humidity of the surrounding air:- aw= RH/1OO) to minimise or prevent growth of E. coli and similar pathogens.