108 Meat refrigeration Table 6.4 Ratio of the peak to the average rate of heat release from 140 kg beef sides, for chiller cycle time of 24 h from I h post-mortem Chiller conditions ak to average ratio Air speed (ms) Temperature Loading period C 0.5 2.0 3.0 3.4 04040404 22446688 4433 33025834 4.3 3.0 6 2.3 2.5 Source: Cox and Bailey, 1978 Table 6.5 Ratio of actual to average heat load ratios for 140 kg beef side in air at0C, 1.0ms", for a chiller cycle time of 24 h from Ih post-mortem Time after start Heat load ratios at Time after start Heat load ratios at of chill (h end of period shown of chill (h) end of period shown 6 46802 0.8 0.3 Source: Cox and Bailey, 1978 Peak load data charts have also been produced in South Africa(Kerens, 1981) for two air temperatures (0 and 7C), an air velocity of 0.75ms and 95% relative humidity. They are expressed in terms of peak heat loss rate against a loading rate in cattle units per hour. A cattle unit is defined as a whole carcass and the average whole carcass weight is 210kg In a typical South African situation a plant operating at 0C, 0.75ms would be loaded over a 3 h period at a rate of 200 cattle units h". The peak heat loss rate from the 600 carcasses would be 550kw. It is stated that using three chill rooms, each with a capacity of 200 carcasses(400 sides), the fan powe required would be 60kw and the heat infiltration 105kw, of which 90k infiltrates through the doors. Thus, the total peak load on the refrigeration plant would be 715kw 6.2.1.4 Cost of chilling operation Data were obtained from a survey of 14 commercial beef chilling systems (Gigiel and Collett, 1990). They ranged in capacity from 18000 to 93000kg
Peak load data charts have also been produced in South Africa (Kerens, 1981) for two air temperatures (0 and 7 °C), an air velocity of 0.75 m s-1 and 95% relative humidity. They are expressed in terms of peak heat loss rate against a loading rate in cattle units per hour. A cattle unit is defined as a whole carcass and the average whole carcass weight is 210kg. In a typical South African situation a plant operating at 0°C, 0.75 m s-1 would be loaded over a 3 h period at a rate of 200 cattle units h-1 . The peak heat loss rate from the 600 carcasses would be 550 kW. It is stated that using three chill rooms, each with a capacity of 200 carcasses (400 sides), the fan power required would be 60 kW and the heat infiltration 105 kW, of which 90 kW infiltrates through the doors. Thus, the total peak load on the refrigeration plant would be 715 kW. 6.2.1.4 Cost of chilling operation Data were obtained from a survey of 14 commercial beef chilling systems (Gigiel and Collett, 1990). They ranged in capacity from 18 000 to 93 000 kg 108 Meat refrigeration Table 6.4 Ratio of the peak to the average rate of heat release from 140 kg beef sides, for chiller cycle time of 24 h from 1 h post-mortem Chiller conditions Peak to average ratio Temperature Loading period Air speed (m s-1 ) (°C) (h) 0.5 1.0 2.0 3.0 0 2 3.4 3.3 4.3 4.0 4 2 4.1 3.7 4.3 4.3 0 4 2.9 2.8 3.0 3.0 4 4 3.1 2.7 3.2 3.1 0 6 2.5 2.5 2.5 2.6 4 6 2.7 2.3 2.8 2.7 0 8 2.3 2.5 2.3 2.4 4 8 2.6 2.3 2.4 2.5 Source: Cox and Bailey, 1978. Table 6.5 Ratio of actual to average heat load ratios for 140 kg beef side in air at 0 °C, 1.0 m s-1 , for a chiller cycle time of 24 h from 1 h post-mortem Time after start Heat load ratios at Time after start Heat load ratios at of chill (h) end of period shown of chill (h) end of period shown 2 3.3 14 0.6 4 2.3 16 0.4 6 1.5 18 0.4 8 1.2 20 0.4 10 0.8 22 0.3 12 0.7 Source: Cox and Bailey, 1978
Primary chilling of red meat 109 Table 6.6 Average ambient air temperature over survey. The energy used per kilogram of beef produced divided into the base demand and the product emand, and"the total energy consumption per kg adjusted to allow for a full Chiller Ambient air (°C) ,e,d=, number 4.0 .0 14.0 43.0 15.0 78.0 128.0 62.6 0.0 48.0 81.0 14.0 2.0 154.0 19.0 33.0 62.3 115.0 21.0 22.6 67.0 116.0 42.0 0 30.0 14.0 18.0 40.0 628 45.8 1020187.0 40.0 143.0 18.0 53.0 Means 47.4 14.6 Source: Gigiel and Collett. 1990 (mean 30625 kg) of beef in carcass form and in size from 216 to 1124m The energy data were broken down into a base demand and a produc demand(Table 6.6). Base demand is the energy required to maintain the chiller at the desired temperature with the doors closed. Product demand is the additional energy needed to reduce the temperature of the meat. When carcasses are loaded into a chilling system the infiltration of warm air through the open doors further adds to the load on the refrigeration plant and this is included in the product load values. The base demand will depend on the average ambient air temperature, the level of insulation, the fan power and the control system used. Plant 1 achieved a zero-base demand in the winter because the control system cut out the fans and compressor when the desired room temperature was reached. The other plants were controlled such that all the evaporator fans ran continuously, except during defrosts, resulting in considerable base demands. To aid comparison, where chillers were not fully loaded, specific energy consumption for full loading was calculated by multiplying product demand per kilogram for a partially loaded chiller by its total capacity and adding this to the base demand Approximately 48h were required in the commercial chillers to meet the EC requirement of a maximum carcass temperature of 7"C (Table 6.7)and side temperatures of up to 17.0C were measured on dispatch from one of
(mean 30 625 kg) of beef in carcass form and in size from 216 to 1124 m3 . The energy data were broken down into a base demand and a product demand (Table 6.6). Base demand is the energy required to maintain the chiller at the desired temperature with the doors closed. Product demand is the additional energy needed to reduce the temperature of the meat. When carcasses are loaded into a chilling system the infiltration of warm air through the open doors further adds to the load on the refrigeration plant and this is included in the product load values. The base demand will depend on the average ambient air temperature, the level of insulation, the fan power and the control system used. Plant 1 achieved a zero-base demand in the winter because the control system cut out the fans and compressor when the desired room temperature was reached. The other plants were controlled such that all the evaporator fans ran continuously, except during defrosts, resulting in considerable base demands. To aid comparison, where chillers were not fully loaded, specific energy consumption for full loading was calculated by multiplying product demand per kilogram for a partially loaded chiller by its total capacity and adding this to the base demand. Approximately 48 h were required in the commercial chillers to meet the EC requirement of a maximum carcass temperature of 7 °C (Table 6.7) and side temperatures of up to 17.0 °C were measured on dispatch from one of Primary chilling of red meat 109 Table 6.6 Average ambient air temperature over survey. The energy used per kilogram of beef produced divided into the base demand and the product demand, and *the total energy consumption per kg adjusted to allow for a full chiller Chiller Ambient air Base First Second *First *For 48 h system temperature demand 24 h 24 h 24 h (kJ kg-1 ) identity (°C) (kJ kg-1 ) (kJ kg-1 ) (kJ kg-1 ) (kJ kg-1 ) number 1 4.0 0.0 63.0 5.8 63.0 68.8 2 14.0 35.0 43.0 15.0 78.0 128.0 3 7.5 26.0 62.6 – 86.0 – 4 0.0 15.0 48.0 3.0 63.0 81.0 5 14.0 38.0 42.0 36.0 80.0 154.0 6 19.0 33.0 62.3 5.3 86.0 115.0 7 21.0 56.7 22.6 5.6 67.0 116.0 8 11.0 44.0 42.0 9.0 86.0 139.0 9 0.0 32.0 30.0 14.0 62.0 108.0 10 4.0 26.0 31.8 7.9 52.0 80.0 11 18.0 40.0 62.8 45.8 102.0 187.0 12 10.5 24.0 53.0 – 77.0 – 13 14.0 40.0 47.7 18.8 86.0 143.0 14 18.0 44.0 53.0 9.0 97.0 150.0 Means 32.4 47.4 14.6 77.5 122.5 Source: Gigiel and Collett, 1990
110 Meat refrigeration Table 6.7 Average weight of sides, average air velocity over deep leg, average chiller temperature over and at end of 24 h, deep leg temperature after 24 h and when removed from chiller, time of removal from chiller and percentage weight Chiller number velocity temperature temperature removal h removal °C)(°C)(°C)(C 40 44.01.181.45 000 152 0.66 8.04015.012.0 26.0179 3.01015.63.9 50.0 182 0.7512.53.017017.0 0.34 905.018.5 6.020190 14.5 320 0.751003.0 Means 0.48 6.52.715.9 92 3851.61.93 Source: Gigiel and Collett, 1990. the chillers. Specific energy consumption for the first 24 h of chilling varied from 57. 8 to 78kJkg" in the winter to 78 to 102.8kJkg" in the summer. Substantially less energy was required in the subsequent 24 h ranging from 3.0 to 45. 8kJkg(average 14.1kJkg Weight losses ranged from 1.18 to 2.06% for the first day of chilling and from 1.45 to 2.31% for 2 days. The cost of this loss was on average 20 times he energy cost and therefore of greater economic importance. Plant 1 had the lowest weight loss and energy consumption and achieved a maximum meat temperature of 5.8C after 44h. It can therefore be used as a target for chill room design and operation. This target would requ uire a maximum energy consumption over 48h of 44kJkg in winter, 140kJkg in summer and a maximum weight loss of 1.5% 6.2.2 Lamb, mutton and goat chilling Many conventional chilling systems for lamb carcasses fail to produce optimal textural qualities or minimum weight losses. No publications have been found on large scale systematic investigations of lamb chilling that are similar to those that have been carried out on beef
the chillers. Specific energy consumption for the first 24 h of chilling varied from 57.8 to 78 kJ kg-1 in the winter to 78 to 102.8 kJ kg-1 in the summer. Substantially less energy was required in the subsequent 24 h ranging from 3.0 to 45.8 kJ kg-1 (average 14.1 kJ kg-1 ). Weight losses ranged from 1.18 to 2.06% for the first day of chilling and from 1.45 to 2.31% for 2 days. The cost of this loss was on average 20 times the energy cost and therefore of greater economic importance. Plant 1 had the lowest weight loss and energy consumption and achieved a maximum meat temperature of 5.8 °C after 44 h. It can therefore be used as a target for chill room design and operation. This target would require a maximum energy consumption over 48 h of 44kJ kg-1 in winter, 140 kJ kg-1 in summer and a maximum weight loss of 1.5%. 6.2.2 Lamb, mutton and goat chilling Many conventional chilling systems for lamb carcasses fail to produce optimal textural qualities or minimum weight losses. No publications have been found on large scale systematic investigations of lamb chilling that are similar to those that have been carried out on beef. 110 Meat refrigeration Table 6.7 Average weight of sides, average air velocity over deep leg, average chiller temperature over and at end of 24 h, deep leg temperature after 24 h and when removed from chiller, time of removal from chiller and percentage weight loss Chiller Average Air Chiller Side Time of Weight number side velocity temperature temperature removal loss weight (m s-1 ) mean end after on (h) (kg) after after 24 h 24 h 24 h removal 24 h 48 h (°C) (°C) (°C) (°C) (%) (%) 1 128 0.49 3.0 0.0 10.8 5.8 44.0 1.18 1.45 2 138 0.27 4.0 2.0 10.8 10.8 24.0 1.75 – 3 148 0.90 1.5 0.0 11.9 9.0 26.5 1.36 – 4 178 0.60 3.0 6.0 14.5 8.0 48.0 1.46 1.66 5 152 0.66 8.0 4.0 15.0 12.0 26.0 1.79 – 6.1 145 0.08 3.0 1.0 15.6 3.9 50.0 1.82 – 6.2 137 0.08 3.0 1.0 – – – – 2.31 7 129 0.75 12.5 3.0 17.0 17.0 24.0 1.61 – 8 130 0.40 5.5 1.0 17.5 7.0 48.0 1.66 – 9 163 0.34 9.0 5.0 18.5 8.6 48.0 1.67 – 10 – 0.20 6.0 2.0 19.0 9.0 44.0 1.12 – 11 152 0.41 16.5 7.0 19.8 4.4 48.0 1.89 – 12 154 0.90 7.0 2.0 20.0 14.5 32.0 1.43 – 13 142 0.33 6.0 4.0 – – – 2.06 2.3 14 – 0.75 10.0 3.0 – – – – – Means 146 0.48 6.5 2.7 15.9 9.2 38.5 1.6 1.93 Source: Gigiel and Collett, 1990