Thermophysical properties of meat 277 Table 13.5 Published enthalpy values of meat Temperature Enthalpy(kJkg) Temperature Enthalpy (kjk (°C) ork Beef Lamb Pork -124-142O 0 -66.0-61.6 -82.1 78.2 1090-106.3-110.5 122.8-1227-127.3 13.2 Freezing, thawing and tempering 13. 2.1 Ice content It is well known that, below its initial freezing point, meat becomes more frozen the lower the temperature. This is due mainly to the fact that freez ing results in an increase in the concentration of the tissue fluids and con- sequently a lower temperature is required for further freezing to occur About 10% of the water content does not appear to freeze even at absolute zero, and it is generally assumed to be too tightly bound to protein, while the remaining 90% of the water content is freezable. Although there is some disagreement between the various investigators about the amount of ice in lean meat at different temperatures, the work of Riedel(1957)is perhaps the most authentic. Figure 13. 1(after Riedel, 1957) shows the percentage of the freezable water that is frozen at different temperatures. Fikiin(1996) has reviewed Eastern European methods of predicting ice content It can be seen that freezing commences at ca -15C and although about half of the freezable water is frozen by -2C, freezing is not entirely com- plete even at-30°C 13.2.2 Heat extraction Figure 13. 2(a)(after Riedel, 1957) shows the heat extraction required in cooling lean meat from 0C to temperatures down to-40C. On the commencement of freezing the heat extraction increases steeply owing to the high latent heat of freezing. Thereafter the heat extraction increases less and less steeply as the formation of ice diminishes, as in Fig 13. 1. For example, in cooling from -1 to -5C the required heat extraction is 193-5=188kJkg", i.e. an average of 47kJkg-C, whereas between -30 and--40C, where freezing is virtually complete, only 1.9kJkgCis aquired. If such calculations were made based on the water content, as is ne in certain refrigeration books, erroneous results can arise, caused mainly by the fact that not all of the water content becomes frozen as is13.2 Freezing, thawing and tempering 13.2.1 Ice content It is well known that, below its initial freezing point, meat becomes more frozen the lower the temperature. This is due mainly to the fact that freez￾ing results in an increase in the concentration of the tissue fluids and con￾sequently a lower temperature is required for further freezing to occur. About 10% of the water content does not appear to freeze even at absolute zero, and it is generally assumed to be too tightly bound to protein, while the remaining 90% of the water content is freezable.Although there is some disagreement between the various investigators about the amount of ice in lean meat at different temperatures, the work of Riedel (1957) is perhaps the most authentic. Figure 13.1 (after Riedel, 1957) shows the percentage of the freezable water that is frozen at different temperatures. Fikiin (1996) has reviewed Eastern European methods of predicting ice content. It can be seen that freezing commences at ca. -1.5 °C and although about half of the freezable water is frozen by -2 °C, freezing is not entirely com￾plete even at -30 °C. 13.2.2 Heat extraction Figure 13.2(a) (after Riedel, 1957) shows the heat extraction required in cooling lean meat from 0 °C to temperatures down to -40 °C. On the commencement of freezing the heat extraction increases steeply owing to the high latent heat of freezing. Thereafter the heat extraction increases less and less steeply as the formation of ice diminishes, as in Fig. 13.1. For example, in cooling from -1 to -5 °C the required heat extraction is 193 - 5 = 188 kJ kg-1 , i.e. an average of 47 kJ kg-1 °C-1 , whereas between -30 and -40 °C, where freezing is virtually complete, only 1.9 kJkg-1 °C-1 is required. If such calculations were made based on the water content, as is done in certain refrigeration books, erroneous results can arise, caused mainly by the fact that not all of the water content becomes frozen as is Thermophysical properties of meat 277 Table 13.5 Published enthalpy values of meat Temperature Enthalpy (kJ kg-1 ) Temperature Enthalpy (kJ kg-1 ) (°C) Pork Beef Lamb (°C) Pork Beef Lamb 40 0 0 0 20 -66.0 -61.6 -62.7 35 -12.4 -14.2 -16.5 15 -82.1 -76.6 -78.2 30 -24.8 -29.4 -32.6 10 -95.7 -91.3 -94.5 25 -41.1 -46.0 -47.7 5 -109.0 -106.3 -110.5 0 -122.8 -122.7 -127.3 Source: Lindsay and Lovatt, 1994