278 Meat refrigeration Fig. 13.1 Percentage of the freezable water that is frozen(source: Morley, 1974) assumed. If, for example, the heat extraction required in cooling lean meat (74% water)between-1 and -5C was calculated in such a manner, a value of 254kJkg- would be obtained, compared with 188kJkg- from Fig 13.2(a) Figure 13. 2(b),(c),(d)and(e)shows the heat extraction required in freezing lamb loin cuts and carcasses(after Fleming, 1969) The mean specific heat of fat in the main meat freezing region(-1 to -20C, for instance), though very variable, is roughly 3kJkg-C,com pared with ca. 7kJ kg" C for bone and 13kJkgC for lean. Thus, the heat extraction required in freezing different meats depends mainly on the quantI 13. 2.3 Thermal conductivity The thermal conductivity of lean meat varies with temperature as shown in ig. 13. 3(after Lentz, 1961). The thermal conductivity of ice is some four times that of water and thus the conductivity of lean meat increases with Increasing I The thermal conductivity of lean meat also depends on the continuity of the ice to the fow of heat the more continuous the ice structure. the greater the conductivity. Thermal conductivity in a direction parallel to muscle fibres is some 8-30% greater than perpendicular to the muscle fibres (Hill et al., 1967; Lentz, 1961). This is due to the fact that ice crystals are parallel to the muscle fibres and thus present a more continuous path for heat flow in this direction. Ice structure also varies with freezing conditions. Slow freezing produces large extracellular columns of ice of greater conti nuity than the small intracellular ice crystals produced by fast freezing. The mean thermal conductivity of fat is ca. 0. 25Wm-C-, which is only about one sixth that of frozen lean. The thermal conductivity of bone variesassumed. If, for example, the heat extraction required in cooling lean meat (74% water) between -1 and -5 °C was calculated in such a manner, a value of 254 kJkg-1 would be obtained, compared with 188kJ kg-1 from Fig. 13.2(a). Figure 13.2(b), (c), (d) and (e) shows the heat extraction required in freezing lamb loin cuts and carcasses (after Fleming, 1969). The mean specific heat of fat in the main meat freezing region (-1 to -20 °C, for instance), though very variable, is roughly 3kJ kg-1 °C-1 , com￾pared with ca. 7 kJkg-1 °C-1 for bone and 13 kJ kg-1 °C-1 for lean. Thus, the heat extraction required in freezing different meats depends mainly on the quantity of lean. 13.2.3 Thermal conductivity The thermal conductivity of lean meat varies with temperature as shown in Fig. 13.3 (after Lentz, 1961). The thermal conductivity of ice is some four times that of water and thus the conductivity of lean meat increases with increasing ice content. The thermal conductivity of lean meat also depends on the continuity of the ice to the flow of heat – the more continuous the ice structure, the greater the conductivity. Thermal conductivity in a direction parallel to the muscle fibres is some 8–30% greater than perpendicular to the muscle fibres (Hill et al., 1967; Lentz, 1961). This is due to the fact that ice crystals are parallel to the muscle fibres and thus present a more continuous path for heat flow in this direction. Ice structure also varies with freezing conditions. Slow freezing produces large extracellular columns of ice of greater conti￾nuity than the small intracellular ice crystals produced by fast freezing. The mean thermal conductivity of fat is ca. 0.25 W m-1 °C-1 , which is only about one sixth that of frozen lean. The thermal conductivity of bone varies 278 Meat refrigeration 100 90 80 70 60 50 40 30 20 10 – 30 – 20 – 10 0 Temperature (°C) Frozen (%) Fig. 13.1 Percentage of the freezable water that is frozen (source: Morley, 1974)