92 Meat refrigeration the surroundings. Therefore, the amount of reflected radiation coming from the surface constitutes a significant error However, the proportion of radiation emitted by a surface relative to that of a perfect black body is the same proportion of incident radiation that would be absorbed by the surface. If the absorbtivity or emissivity of the surface is known and the surface is not transparent, which is true for all packaging materials except some plastics, the reflectance of the surface will also be known by subtracting the absorbtivity from 1. Hence it is possible to calculate the extent of the error Unfortunately this requires a lot of information about the emissivity and eflectance of the various packaging materials and takes a long time. There- fore, the advantage of taking quick accurate readings will be lost The Meat Research Corporation in Australia(1995a)recommend that an infrared thermometer should be permanently located in beef chill rooms. It should be positioned to measure the surface temperature of one of the last sides to be loaded. It can then be used to provide a permanently logged output of surface temperature and control the refrigeration system. When the surface temperature has reached ca. 2C the fan speed can be auto- matically reduced and the suction pressure raised. This will reduce both weight loss and operating cost Infrared systems have also been used to monitor the surface tempera- ture of pig carcasses in chill rooms(Metternick-Jones and Skevington 1992). The thermometer required a minimum stabilisation time of 120min 1C of other methods and were repeatable to the same accurat e within in the chill room. After this time the temperatures measured wer 14.3.3 Contact destructive methods Determining the temperature of small cuts of meat with regular shapes is quite simple. Determining the temperature of irregular cuts of meat, par ticularly large pieces, is more difficult. Possibly the most difficult problem is ascertaining deep leg temperature in beef carcasses The Meat Research Corporation in Australian(1995b)recommend that the temperature sensor should touch the trochanter major (aitch bone), which is the knob'of bone on the opposite side of the femur to the hi nt. To locate the in this position it should be inserted through the pope's eye' at an angle about 15-20 below the horizontal(Fig 14.1).It should be aimed at an imaginary vertical line approximately one-third of the distance from the achilles tendon to the last tailbone Because conduction occurs along the steel shaft of a probe it is impo tant that the probe is inserted as far as possible into the meat. For example, to take the temperature of a cut of meat it is better practice to insert the probe to its full depth along the long axis of the cut rather than to insert the probe to half its length through the short axis(Csiro, 1991) For manufacturers to produce accurate data on the freezing of their meatthe surroundings. Therefore, the amount of reflected radiation coming from the surface constitutes a significant error. However, the proportion of radiation emitted by a surface relative to that of a perfect black body is the same proportion of incident radiation that would be absorbed by the surface. If the absorbtivity or emissivity of the surface is known and the surface is not transparent, which is true for all packaging materials except some plastics, the reflectance of the surface will also be known by subtracting the absorbtivity from 1. Hence it is possible to calculate the extent of the error. Unfortunately this requires a lot of information about the emissivity and reflectance of the various packaging materials and takes a long time. There￾fore, the advantage of taking quick accurate readings will be lost. The Meat Research Corporation in Australia (1995a) recommend that an infrared thermometer should be permanently located in beef chill rooms. It should be positioned to measure the surface temperature of one of the last sides to be loaded. It can then be used to provide a permanently logged output of surface temperature and control the refrigeration system. When the surface temperature has reached ca. 2 °C the fan speed can be auto￾matically reduced and the suction pressure raised. This will reduce both weight loss and operating costs. Infrared systems have also been used to monitor the surface tempera￾ture of pig carcasses in chill rooms (Metternick-Jones and Skevington, 1992). The thermometer required a minimum stabilisation time of 120min in the chill room. After this time the temperatures measured were within 1 °C of other methods and were repeatable to the same accuracy. 14.3.3 Contact destructive methods Determining the temperature of small cuts of meat with regular shapes is quite simple. Determining the temperature of irregular cuts of meat, par￾ticularly large pieces, is more difficult. Possibly the most difficult problem is ascertaining deep leg temperature in beef carcasses. The Meat Research Corporation in Australian (1995b) recommend that the temperature sensor should touch the trochanter major (aitch bone), which is the ‘knob’ of bone on the opposite side of the femur to the hip joint. To locate the sensor in this position it should be inserted through the ‘pope’s eye’ at an angle about 15–20° below the horizontal (Fig 14.1). It should be aimed at an imaginary vertical line approximately one-third of the distance from the Achilles tendon to the last tailbone. Because conduction occurs along the steel shaft of a probe it is impor￾tant that the probe is inserted as far as possible into the meat. For example, to take the temperature of a cut of meat it is better practice to insert the probe to its full depth along the long axis of the cut rather than to insert the probe to half its length through the short axis (CSIRO, 1991). For manufacturers to produce accurate data on the freezing of their meat 292 Meat refrigeration