276 Meat refrigeration Table 13.4 Specific heat of bones Temperature range(°C) kJkg°) Beef (32% water) Pork(34% water Pork(35.4%water 2.39 Pork(bone from che 5-1 Pork(bone from chops) 5-38.5 Pork(rib 31. 5% water) Pork(knuckle joint) Chicken(35.6% water) Source: Morley. 1972b It can be seen that there is quite a small variation in the specific heat of different types of lean meat, whereas there is a relatively large variation in the specific heats of different fats. The specific heat of fat also varies greatly with temperature. This is due to latent heat associated with phase changes. The temperatures at which these occur depend on the type of fat. Studies by Morley and Fursey(1988) have shown that the values of specific heat and enthalpy change in fats measured during cooling differ from those measured during subsequent heating. This suggested that further fat solid ification occurred during storage. Using thermal data obtained in inappro- priate conditions could lead to errors in prediction of temperature changes The variability in the specific heat of fats with temperature should result in corresponding, though smaller, variations in the specific heats of cuts and ses,although no detailed investigations have been undertaken to show this. The effect of carcass composition variations on the mean specific heat in chilling can be estimated. The result is a total variation of about +0.o5 from the specific heat of an average beef, pork or lamb carcass. There appears to be little difference between the specific heats of typical beef, pork and lamb carcasses. Many specific heat tables for foods (e.g. ASHRAE Guide and Data Books)are based on Siebel's formula of 1892, i.e. calculated from the water content,assuming the solid content has a specific heat of 0. 2 btu/bF. This can obviously result in considerable error, as for example in estimating the mean specific heat in chilling a typical beef, pork or lamb carcass Siebels formula gives a value that is about 35% too low 13.1.3 Enthalpies Published enthalpy values for meat are shown in Table 13.5. Further data for lean pork, pork sausage meat, beef sausage meat, beef mince, beef fat and pork kidney fat over the temperature range -40 to +40C can be found in Lindsay and Lovatt(1994)It can be seen that there is quite a small variation in the specific heat of different types of lean meat, whereas there is a relatively large variation in the specific heats of different fats. The specific heat of fat also varies greatly with temperature. This is due to latent heat associated with phase changes. The temperatures at which these occur depend on the type of fat. Studies by Morley and Fursey (1988) have shown that the values of specific heat and enthalpy change in fats measured during cooling differ from those measured during subsequent heating. This suggested that further fat solid￾ification occurred during storage. Using thermal data obtained in inappro￾priate conditions could lead to errors in prediction of temperature changes. The variability in the specific heat of fats with temperature should result in corresponding, though smaller, variations in the specific heats of cuts and carcasses, although no detailed investigations have been undertaken to show this. The effect of carcass composition variations on the mean specific heat in chilling can be estimated. The result is a total variation of about ±0.05 from the specific heat of an average beef, pork or lamb carcass. There appears to be little difference between the specific heats of typical beef, pork and lamb carcasses. Many specific heat tables for foods (e.g. ASHRAE Guide and Data Books) are based on Siebel’s formula of 1892, i.e. calculated from the water content, assuming the solid content has a specific heat of 0.2 btu/lb °F. This can obviously result in considerable error, as for example in estimating the mean specific heat in chilling a typical beef, pork or lamb carcass. Siebel’s formula gives a value that is about 35% too low. 13.1.3 Enthalpies Published enthalpy values for meat are shown in Table 13.5. Further data for lean pork, pork sausage meat, beef sausage meat, beef mince, beef fat and pork kidney fat over the temperature range -40 to +40 °C can be found in Lindsay and Lovatt (1994). 276 Meat refrigeration Table 13.4 Specific heat of bones Type Temperature Specific heat range (°C) (kJ kg-1 °C-1 ) Beef (32% water) 0–18 2.46 Pork (34% water) 0–20 2.85 Pork (35.4% water) 0–19 2.39 Pork (bone from chops) 5–15 2.40 Pork (bone from chops) 5–38.5 2.75 Pork (rib 31.5% water) 5–15 2.21 Pork (knuckle joint) 5–15 2.23 Chicken (35.6% water) 0–21 2.92 Source: Morley, 1972b