Evaluation of the immersion vacuum cooling of cooked beef joints - mathematical simulation of variations in beef size and porosity and pressure reduction rates.

摘要

A detailed evaluation of the influence of variations in product (beef size and porosity) and process parameters (vacuum chamber pressure reduction rate) on cooling time, total mass loss, pressure and temperature distributions during the immersion vacuum cooling of large cooked beef joint samples was performed using a previously developed and validated mathematical model. Beef size variations were done by changing radius values (between 5.5 and 8 cm) and porosity levels (between 2 and 5%). Pressure reductions rates varied between circa 5 to 25 mbar/min. The simulation indicated that using the maximum pressure drop rate tested (circa 25 mbars/min) beef samples (3% porosity) of up to 6.5 and 7 cm radius can be cooled within Irish and American official safety guidelines, respectively. An increase in porosity could further reduce cooling time but incur higher mass losses, which can be detrimental to product quality. The identified effects and relevant trends due to variations on the different parameters studied on the cooling process performance lead to recommendations in relation to optimal pressure drop rate, in relation to size and porosity ranges. Necessary modifications to the equipment design, such as the introduction of agitation in the cooling medium, are also emphasised. Industrial relevance: Meat is typically cooked before consumption, and if it is not for immediate consumption, it should be cooled as soon as possible thereafter. Commercial products such as large cured and precooked meat pieces undergo heat treatment, and hence need to be cooled prior to packing, storage and distribution. Product temperature should be reduced as quickly as possible to its final target, to minimise quality loss and prevent or minimise microbial growth or spore germination. After relatively mild heat treatments such as pasteurisation (heat processes in the range of 60-80 degrees C) the microorganisms of concern are often heat resistant micro flora such as mesophilic spores of Bacillus and Clostridium species that under adequate conditions might germinate and grow, posing a safety risk. The difficulties of cooling large commercial meat pieces or joints have been reported, and the responsibility is on manufacturers to ensure that procedures are adequate and safety risks are minimised. Recent investigations into vacuum cooling have shown advances for the meat industry