《肉制品冷冻技术》（英文版） Part 6 TThe cold chain from carcass to consumer

Part 2 TThe cold chain from carcass to consumer

Part 2 The cold chain from carcass to consumer

Primary chilling of red meat 6.1 Introduction The increased application of temperature legislation in many countries. coupled with economic requirements to maximise throughput, minimise weight loss and operate refrigeration systems in the most efficient manner, has created a very large demand for process design data on all aspects of carcass chilling Concurrently there has been a growing realisation of the importance of chilling rate on meat saleability, in terms of drip potential (see Chapter 2), appearance(see Chapter 4), and eating quality, particu- larly texture(see Chapter 3). EU temperature legislation governs the chilling of beef, pork and lamb for the majority of abattoirs within the community. The only derogations are for very small abattoirs and for retail shops cutting meat for direct sale to the final consumer. The EC legislation does not define a chilling time, only a maximum final meat temperature of 7C before transport or Abattoir management and refrigeration contractors require reliable design data, relating processing variables to chilling time and weight loss, so that they can specify and design carcass cooling systems to meet differ ng requirements To optimise fully such systems, knowledge is also required of the product heat load, and its variation with time, so that the refrigera tion machinery can be sized to achieve the required throughput It is also important that the industry is made aware of a growing number of alternatives to conventional batch air chilling systems. Many of the alter native systems offer significant advantages in terms of increased through- put, lower costs and increased product quality

6 Primary chilling of red meat 6.1 Introduction The increased application of temperature legislation in many countries, coupled with economic requirements to maximise throughput, minimise weight loss and operate refrigeration systems in the most efficient manner, has created a very large demand for process design data on all aspects of carcass chilling. Concurrently there has been a growing realisation of the importance of chilling rate on meat saleability, in terms of drip potential (see Chapter 2), appearance (see Chapter 4), and eating quality, particu￾larly texture (see Chapter 3). EU temperature legislation governs the chilling of beef, pork and lamb for the majority of abattoirs within the community. The only derogations are for very small abattoirs and for retail shops cutting meat for direct sale to the final consumer. The EC legislation does not define a chilling time, only a maximum final meat temperature of 7 °C before transport or cutting. Abattoir management and refrigeration contractors require reliable design data, relating processing variables to chilling time and weight loss, so that they can specify and design carcass cooling systems to meet differ￾ing requirements.To optimise fully such systems, knowledge is also required of the product heat load, and its variation with time, so that the refrigera￾tion machinery can be sized to achieve the required throughput. It is also important that the industry is made aware of a growing number of alternatives to conventional batch air chilling systems. Many of the alter￾native systems offer significant advantages in terms of increased through￾put, lower costs and increased product quality

100 Meat refrigeration 6.2 Conventional chilling The majority of carcass meat is chilled in conventional chill rooms nomi nally operating at one or sometimes two conditions during the chilling cycle Most of the factors that control the chilling process are common to all species and are covered in the following section on beef. Specific consid- erations for sheepmeat, pork and offal are outlined in their respective sections. 6.2.1 Beef This section brings together design data on many aspects of the chilling of beef sides. Effects of environmental, carcass and operational variables on the rate of chilling and evaporative weight loss in single stage air chilling systems are described in detail. Data are also presented on the rate of heat release from sides that are encountered in these cooling operations Using conventional single stage chilling regimes it is evident that only relatively light(<105 kg), lean beef sides can be cooled to 7C in the deep leg during a 24 h operating cycle, whilst evaporative losses are of the order of 2% Despite the general absence of specific regulations for chilling time, the time required to cool a side to a specified maximum temperature is the most important commercial factor determining the cost and operation of a cooling system. If sides cannot be chilled within 18h, which is the time avail able in one day, making allowance for loading, unloading and cleaning, they will probably remain in chill for a further 24 h. Chilling facilities will then have to be twice as large, with considerably increased capital investment and running costs. Some investigations on the continuous chilling of beef (Drumm et al., 1992a, b) have been carried out but such systems are not widely used Increasing attention is now being paid to the reduction in energy con sumption, but it has been shown that in commercial chilling operations the cost of evaporative weight loss in beef sides(Collett and Gigiel, 1986)are at least an order of magnitude higher than the energy costs. Major investigations to provide such data have been carried out at Food Refrigeration and Process Engineering Research Centre(FRPERC) Langford(formerly the Meat Research Institute)(Bailey and Cox, 1976; Cox and Bailey, 1978)and at the National Mechanical Engineering Research Institute, Pretoria(Kerens and Visser, 1978; Kerens, 1981). Pub- lished information from these investigations and others has been brought together in this section together with some unpublished material 6.2.1.1 Effect of environmental and carcass variables on cooling rate Air temperature, air velocity, and to a limited extent, relative humidity, are the environmental factors that affect the cooling time of beef sides. Cooling rate will also be a function of the weight and fat cover of a given side

6.2 Conventional chilling The majority of carcass meat is chilled in conventional chill rooms nomi￾nally operating at one or sometimes two conditions during the chilling cycle. Most of the factors that control the chilling process are common to all species and are covered in the following section on beef. Specific consid￾erations for sheepmeat, pork and offal are outlined in their respective sections. 6.2.1 Beef This section brings together design data on many aspects of the chilling of beef sides. Effects of environmental, carcass and operational variables on the rate of chilling and evaporative weight loss in single stage air chilling systems are described in detail. Data are also presented on the rate of heat release from sides that are encountered in these cooling operations. Using conventional single stage chilling regimes it is evident that only relatively light (<105 kg), lean beef sides can be cooled to 7 °C in the deep leg during a 24 h operating cycle, whilst evaporative losses are of the order of 2%. Despite the general absence of specific regulations for chilling time, the time required to cool a side to a specified maximum temperature is the most important commercial factor determining the cost and operation of a cooling system. If sides cannot be chilled within 18h, which is the time avail￾able in one day, making allowance for loading, unloading and cleaning, they will probably remain in chill for a further 24h. Chilling facilities will then have to be twice as large, with considerably increased capital investment and running costs. Some investigations on the continuous chilling of beef (Drumm et al., 1992a,b) have been carried out but such systems are not widely used. Increasing attention is now being paid to the reduction in energy con￾sumption, but it has been shown that in commercial chilling operations the cost of evaporative weight loss in beef sides (Collett and Gigiel, 1986) are at least an order of magnitude higher than the energy costs. Major investigations to provide such data have been carried out at Food Refrigeration and Process Engineering Research Centre (FRPERC), Langford (formerly the Meat Research Institute) (Bailey and Cox, 1976; Cox and Bailey, 1978) and at the National Mechanical Engineering Research Institute, Pretoria (Kerens and Visser, 1978; Kerens, 1981). Pub￾lished information from these investigations and others has been brought together in this section together with some unpublished material. 6.2.1.1 Effect of environmental and carcass variables on cooling rate Air temperature, air velocity, and to a limited extent, relative humidity, are the environmental factors that affect the cooling time of beef sides. Cooling rate will also be a function of the weight and fat cover of a given side. 100 Meat refrigeration

Primary chilling of red meat 101 6.2.1.1.1 Air temperature The results of the programme on beef chilling carried out at Langford clearly show the importance of air temperature on cooling time( Bailey and Cox, 1976). For ease of use the results of the investigations have been pre- sented as four plots of the logarithm of temperature against time covering wide range of side weights(100-220kg)and air velocities(0.5-3.0ms") Data for the slowest cooling area of the side, which was located by insert ing a probe into the centre of the thickest section of the leg, are Fig 6.1 and can therefore be used to determine the environmental condi tions required to attain a desired cooling time when a maximum final tem- perature has been specified Potential surface freezing problems can then be evaluated from the surface temperature plots(Figs. 6.2 and 6.3). These conjunction with the deep M. longissimus dorsi data(Fig. 6. 4) also identify toughening problems and the possible requirement for electrical stimulatio Cooling in air at a constant 4C, compared with 0'C, at 3ms wil crease the time to reach 7C in the deep leg of a 100kg side from 20.3 to 277h(a 36%increase). At 0.5ms, the time for a 220kg side to reach 7C will increase from 45.9 to 683h(a 49% increase). In systems designed to produce fully chilled sides, with average meat temperatures of 2-4C, the requirement for low air temperatures becomes even more important because of the small meat/air temperature difference at the end of the process. + Approximate average for British abattoirs 十哪四32232230 05105002 Time post-mortem ig. 6.1 Relationship between deep longissimus dorsi temperature and cooling time for beef sides(source: Bailey and Cox, 1976)

6.2.1.1.1 Air temperature The results of the programme on beef chilling carried out at Langford clearly show the importance of air temperature on cooling time (Bailey and Cox, 1976). For ease of use the results of the investigations have been pre￾sented as four plots of the logarithm of temperature against time covering a wide range of side weights (100–220 kg) and air velocities (0.5–3.0 ms-1 ). Data for the slowest cooling area of the side, which was located by insert￾ing a probe into the centre of the thickest section of the leg, are shown in Fig. 6.1 and can therefore be used to determine the environmental condi￾tions required to attain a desired cooling time when a maximum final tem￾perature has been specified. Potential surface freezing problems can then be evaluated from the surface temperature plots (Figs. 6.2 and 6.3). These in conjunction with the deep M. longissimus dorsi data (Fig. 6.4) also identify toughening problems and the possible requirement for electrical stimulation. Cooling in air at a constant 4°C, compared with 0 °C, at 3m s-1 will increase the time to reach 7 °C in the deep leg of a 100kg side from 20.3 to 27.7 h (a 36% increase). At 0.5 ms-1 , the time for a 220 kg side to reach 7 °C will increase from 45.9 to 68.3 h (a 49% increase). In systems designed to produce fully chilled sides, with average meat temperatures of 2–4 °C, the requirement for low air temperatures becomes even more important because of the small meat/air temperature difference at the end of the process. Primary chilling of red meat 101 38·5 38·5 38·5 35 35 35 30 30 30 25 25 25 20 20 20 15 15 15 10 10 7 5 4 3 7 10 2 1 5 9 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 0·01 0·02 0·03 0·04 0·05 0·06 0·07 0·08 0·09 0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0 0·5 0·5 0·5 Y 1 1 3 2 2 1 0·5 3 21 3 Air speed (m s 3 2 –1) Time post-mortem (h) Deep long. dorsi temperature (°C) Chiller air temperature (°C) 840 Side weights 100 140 180 220 Approximate average for British abattoirs kg Fig. 6.1 Relationship between deep longissimus dorsi temperature and cooling time for beef sides (source: Bailey and Cox, 1976)

Side weights kg 40--Approximate average for British abattoirs e品a Air speed(m s-)→32 Time post-mortem(h) Fig. 6.2 Relationship between deep leg temperature and cooling time for beef sides(source: Bailey and Cox, 1976) Side weights 140--Approximate average for British abattoirs 18- g2巴E28o8E0 Air speed(m.)→3232 0.02 Time post-mortem(h) Fig 6.3 Relationship between surface longissimus dorsi temperature and cooling time for beef sides(source: Bailey and Cox, 1976)

38·5 35 30 25 20 15 10 7 5 4 3 2 1 38·5 35 30 25 20 15 10 7 5 38·5 35 30 25 20 15 10 9 0 8 16 24 32 40 48 56 64 72 80 88 96 104 0·01 0·02 0·03 0·04 0·05 0·06 0·07 0·08 0·09 0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0 0·5 0·5 0·5 Y 1 1 3 2 2 0·5 1 3 2 1 3 2 3 Air speed (m s–1) Time post-mortem (h) Deep leg temperature (°C) Chiller air temperature (°C) 8 4 0 Side weights kg 100 140 180 220 Approximate average for British abattoirs Fig. 6.2 Relationship between deep leg temperature and cooling time for beef sides (source: Bailey and Cox, 1976). 38·5 38·5 38·5 35 35 30 30 25 25 20 20 15 15 10 7 10 35 30 25 20 15 10 7 5 4 3 2 1 5 9 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0·01 0·02 0·03 0·04 0·05 0·06 0·07 0·08 0·09 0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0 0·5 0·5 0·5 Y 1 2 2 1 1 0·5 3 2 1 3 3 Air speed (m s 3 2 –1) Time post-mortem (h) Surface long. dorsi temperature (°C) Chiller air temperature (°C) 840 Side weights kg 100 140 180 220 Approximate average for British abattoirs Fig. 6.3 Relationship between surface longissimus dorsi temperature and cooling time for beef sides (source: Bailey and Cox, 1976)

Primary chilling of red meat 103 Side weights +Approximate average for British abattoirs Air speed (ms-1)+3 \21.N 9.5 80 Time post-mortem(h) Fig 6.4 Relationship between surface leg temperature and cooling time for beef Provided air temperatures are chosen to avoid substantial surface freez ing it is quite feasible to determine the cooling time for any other air tem- perature using Figs. 6.1 to 6.4. The fractional unaccomplished temperature on the Y axis can be replaced by the meat temperature calculated by where t is the meat temperature, ti is the initial meat temperature and tf is he air temperature The experimental data used to produce the figures were obtained powerful refrigeration systems where the initial temperature pull down period was minimal. Commercial systems with long pull down periods take considerably longer to cool because initial air temperatures are higher than the required design figure 6.2.1. 1.2 Air velocity Increasing the air velocity during chilling produces a substantial reduction in chilling times at low air velocity but similar increases at higher velocities have a much smaller effect Table 6.1)

Provided air temperatures are chosen to avoid substantial surface freez￾ing it is quite feasible to determine the cooling time for any other air tem￾perature using Figs. 6.1 to 6.4. The fractional unaccomplished temperature on the Y axis can be replaced by the meat temperature calculated by: [6.1] where t is the meat temperature, ti is the initial meat temperature and tf is the air temperature. The experimental data used to produce the figures were obtained in powerful refrigeration systems where the initial temperature pull down period was minimal. Commercial systems with long pull down periods take considerably longer to cool because initial air temperatures are higher than the required design figure. 6.2.1.1.2 Air velocity Increasing the air velocity during chilling produces a substantial reduction in chilling times at low air velocity but similar increases at higher velocities have a much smaller effect (Table 6.1). Y tt t t = - ( )f if ( ) - Primary chilling of red meat 103 38·5 38·5 38·5 35 35 35 30 30 25 25 20 20 15 15 10 7 10 30 25 20 15 10 7 5 4 3 2 1 5 9 0 8 16 24 32 40 48 56 64 72 800·01 0·02 0·03 0·04 0·05 0·06 0·07 0·08 0·09 0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0 0·5 0·5 0·5 Y 1 1 2 2 1 0·5 3 2 1 3 3 Air speed (m s–1) 3 2 Time post-mortem (h) Surface leg temperature (°C) Chiller air temperature (°C) 8 4 0 Side weights kg 100 140 180 220 Approximate average for British abattoirs Fig. 6.4 Relationship between surface leg temperature and cooling time for beef sides (source: Bailey and Cox, 1976)

104 Meat refrigeration Table 6.1. Chilling time (in h)to a deep bone temperature of 10"C in beef sides 3.0ms-i d 140kg in air at 0C, 95% relative humidity at air velocities from 0.5 to Reference Side weight(kg) Air velocity(ms") erens andⅤ Isser 518.518016.014.8 Kerens and visser 140 24.122821.819718.5 Bailey and cox 140 25.022.1200 (1976) The power required by the fans to move the air increases with the cube of the velocity. A four-fold increase in air velocity from 0.5 to 2ms results n a 47h reduction in chilling time for a 140 kg side weight, but requires a 64-fold increase in fan power. Further increasing air velocity to 3 ms- only achieves an extra 6-8% reduction in chilling time. In most practical situations it is doubtful whether an air velocity greater than 1 ms can be justified 6. 2.1.1.3 Relative humidity A small number of investigations(Kerens and Visser, 1978)have shown hat decreased relative humidity(rh) results in slight reduction in chilling time, apparently caused by increased evaporative cooling from the carc surface. However, unless water is added to the surface of the carcass, any increase in the rate of evaporation will be directly reflected in a larger weight loss. It is therefore difficult to envisage a commercial situation where the installation of small, high temperature difference(TD)evaporators with attendant lower relative humidities would be economically viable 6. 2.1.1.4 Side weight The marked effect of side weight on chilling time(Table 6.2)is a clear problem in chill room design and operation. In most practical situations it is impossible to load chilling systems with batches of matched weight sides or to remove sides in a weight-based order. A compromise must therefore be made between overcooling the light-weight sides and undercooling heavy sides. Overcooling can lead to excessive weight loss while under cooling can shorten shelf-life and overload the refrigeration systems of transport vehicles. Subsequent slow cooling in transport vehicles results in a further reduction in shelf-life 6.2.1.1.5 Fat cover It is difficult to separate the effect of fat cover from that of carcass weight Experimental investigations are hampered because light animals tend to be

The power required by the fans to move the air increases with the cube of the velocity. A four-fold increase in air velocity from 0.5 to 2ms-1 results in a 4–7 h reduction in chilling time for a 140 kg side weight, but requires a 64-fold increase in fan power. Further increasing air velocity to 3 m s-1 only achieves an extra 6–8% reduction in chilling time. In most practical situations it is doubtful whether an air velocity greater than 1 m s-1 can be justified. 6.2.1.1.3 Relative humidity A small number of investigations (Kerens and Visser, 1978) have shown that decreased relative humidity (RH) results in slight reduction in chilling time, apparently caused by increased evaporative cooling from the carcass surface. However, unless water is added to the surface of the carcass, any increase in the rate of evaporation will be directly reflected in a larger weight loss. It is therefore difficult to envisage a commercial situation where the installation of small, high temperature difference (TD) evaporators with attendant lower relative humidities would be economically viable. 6.2.1.1.4 Side weight The marked effect of side weight on chilling time (Table 6.2) is a clear problem in chill room design and operation. In most practical situations it is impossible to load chilling systems with batches of matched weight sides or to remove sides in a weight-based order. A compromise must therefore be made between overcooling the light-weight sides and undercooling heavy sides. Overcooling can lead to excessive weight loss while under￾cooling can shorten shelf-life and overload the refrigeration systems of transport vehicles. Subsequent slow cooling in transport vehicles results in a further reduction in shelf-life. 6.2.1.1.5 Fat cover It is difficult to separate the effect of fat cover from that of carcass weight. Experimental investigations are hampered because light animals tend to be 104 Meat refrigeration Table 6.1. Chilling time (in h) to a deep bone temperature of 10 °C in beef sides of 105 and 140 kg in air at 0 °C, 95% relative humidity at air velocities from 0.5 to 3.0 m s-1 Reference Side weight (kg) Air velocity (m s-1 ) 0.5 0.75 1.0 2.0 3.0 Kerens and Visser 105 19.5 18.5 18.0 16.0 14.8 (1978) Kerens and Visser 140 24.1 22.8 21.8 19.7 18.5 (1978) Bailey and Cox 140 27.2 – 25.0 22.1 20.0 (1976)

Primary chilling of red meat 105 Table 6.2 Chilling time(in h) to 7C in the deep leg of 50-220 kg beef sides in air at.C,0.75ms"(source: Kerens and visser, 1978)or"C,1.0ms Conditions 100 0°C,075ms-1 176 274 0°C,1.0ms- 36.0 Source: Bailey and Cox, 1976. lean and heavy animals fat Comparisons can thus only be made over a limited weight range. In the Langford work(Bailey and Cox, 1976)using 140kg sides in air at C,0.5ms, cooling times of the fattest carcasses were as much as 20% above the average and the leanest 20% below. In South Africa(Kerens and Visser, 1978)cooling times at 0C,0.75ms" for fat and lean sides of 100kg were 24.5 and 190h, respectively, and for 125kg, 27 and 22h. res 6.2.1.2 Effect of environmental and carcass variables on weight loss Weight loss is governed by the same variables that affect cooling rate but with different relative importance. 6.2.1.2.1 Air temperature The effect of air temperature on evaporative weight loss during chilling dependent upon the criteria used to define the end of the chilling process (Fig. 6.5). When chilling for a set time(18h) weight loss increases as tem perature decreases. The opposite effect is found when chilling to a set temperature (10C in deep leg) with weight loss decreasing as the air temperature is lowered. However, the magnitude of the effect of air tem perature on weight loss is small, as a reduction in air temperature from 4 to 0C produces a change of <0. 1%(Fig. 6.5)under either criteria 6.2. 1.2.2 Air velocity The effect of air velocity is similar to that of air temperature. An increase from 0.5 to 3. 0ms-I made <0. 1% difference to losses when sides were chilled to a deep leg temperature of 10C. Increasing the air velocity from 0. 75 to 3ms raised weight losses by up to 0. 2% when measured over an 18 h chilling period(Fig. 6.5). In a longer chilling cycle, the effect would be even more severe. Hence there are considerable economic advantages to be gained in systems where the air velocity is reduced after the majority of the heat has been extracted from the carcasses( Gigiel and Peck, 1984) From this time on, the rate of cooling is then determined by thermal con- ductivity of the meat and not by the heat transfer coefficient at its surface In Australia, the Meat Research Corporation(1995)recommends the use of infrared thermometry to automate this process. If the room is also

lean and heavy animals fat. Comparisons can thus only be made over a limited weight range. In the Langford work (Bailey and Cox, 1976) using 140 kg sides in air at 0 °C, 0.5 m s-1 , cooling times of the fattest carcasses were as much as 20% above the average and the leanest 20% below. In South Africa (Kerens and Visser, 1978) cooling times at 0°C, 0.75 m s-1 for fat and lean sides of 100 kg were 24.5 and 19.0h, respectively, and for 125 kg, 27 and 22 h, respectively. 6.2.1.2 Effect of environmental and carcass variables on weight loss Weight loss is governed by the same variables that affect cooling rate but with different relative importance. 6.2.1.2.1 Air temperature The effect of air temperature on evaporative weight loss during chilling is dependent upon the criteria used to define the end of the chilling process (Fig. 6.5). When chilling for a set time (18h) weight loss increases as tem￾perature decreases. The opposite effect is found when chilling to a set temperature (10 °C in deep leg) with weight loss decreasing as the air temperature is lowered. However, the magnitude of the effect of air tem￾perature on weight loss is small, as a reduction in air temperature from 4 to 0 °C produces a change of <0.1% (Fig. 6.5) under either criteria. 6.2.1.2.2 Air velocity The effect of air velocity is similar to that of air temperature. An increase from 0.5 to 3.0 m s-1 made <0.1% difference to losses when sides were chilled to a deep leg temperature of 10 °C. Increasing the air velocity from 0.75 to 3m s-1 raised weight losses by up to 0.2% when measured over an 18 h chilling period (Fig. 6.5). In a longer chilling cycle, the effect would be even more severe. Hence, there are considerable economic advantages to be gained in systems where the air velocity is reduced after the majority of the heat has been extracted from the carcasses (Gigiel and Peck, 1984). From this time on, the rate of cooling is then determined by thermal con￾ductivity of the meat and not by the heat transfer coefficient at its surface. In Australia, the Meat Research Corporation (1995) recommends the use of infrared thermometry to automate this process. If the room is also Primary chilling of red meat 105 Table 6.2 Chilling time (in h) to 7 °C in the deep leg of 50–220 kg beef sides in air at 0 °C, 0.75 m s-1 (source: Kerens and Visser, 1978) or 0 °C, 1.0 m s-1 Conditions Side weight (kg) 50 75 100 140 180 220 0 °C, 0.75 m s-1 13.0 17.6 21.6 27.4 – – 0 °C, 1.0 m s-1 – – 25.6 30.9 36.0 42.1 Source: Bailey and Cox, 1976

106 Meat refrigeration Air speed 3.0 0.75 Fig 6.5 Weight loss during 18 h chilling at an air temperature of 0C at different velocities and relative humidities( source: James and Bailey, 1990) operated as a storage chill, for example over weekends, the need to operate it low air velocities to reduce weight loss and subsequent surface dis- colouration is even more important 6. 2.1.2.3 Relative humidity Relative humidity has a greater effect on weight loss than either air tem perature(see previously) or velocity(Fig. 6.5). Reducing relative humidity from 95 to 80% increased evaporative weight loss over an 18h chilling cycle ato° by nearly0.% 6.2. 1.2.4 Side weight Percentage evaporative weight loss decreases as side weight increases (Table 6.3), the effect being marked at very low side weights(<100kg),but far less so at and above the average side weight for the UK (135 kg) 6.2.1.2.5 Fat cover It is clear from Fig 6.5 that fat cover has a substantial effect on evapora tive weight loss during an 18h chilling period. In the worst circumstances a very lean side with little or no fat cover can lose almost 1% more than sides of similar weight with a thick even covering of fat

operated as a storage chill, for example over weekends, the need to operate at low air velocities to reduce weight loss and subsequent surface dis￾colouration is even more important. 6.2.1.2.3 Relative humidity Relative humidity has a greater effect on weight loss than either air tem￾perature (see previously) or velocity (Fig. 6.5). Reducing relative humidity from 95 to 80% increased evaporative weight loss over an 18 h chilling cycle at 0 °C by nearly 0.5%. 6.2.1.2.4 Side weight Percentage evaporative weight loss decreases as side weight increases (Table 6.3), the effect being marked at very low side weights (<100 kg), but far less so at and above the average side weight for the UK (135 kg). 6.2.1.2.5 Fat cover It is clear from Fig. 6.5 that fat cover has a substantial effect on evapora￾tive weight loss during an 18h chilling period. In the worst circumstances a very lean side with little or no fat cover can lose almost 1% more than sides of similar weight with a thick even covering of fat. 106 Meat refrigeration 3.0 1.5 75 80 85 90 95 0.75 Air speed m s–1 Relative humidity (%) 2.0 2.5 Weight loss (%) Fig. 6.5 Weight loss during 18 h chilling at an air temperature of 0 °C at different velocities and relative humidities (source: James and Bailey, 1990)

Primary chilling of red meat 107 Table 6.3 Effect of side weight on evap loss(%)after cooling for 18 and 42h at 0C. 0.75ms and 95% relative humidity Chilling time Side weight(kg) 110130150 170 2.5 2.4 ource: Bailey and Cox. 1976 6.2. 1.2.6 Operational factors Investigations have been carried out in a commercial chiller that was designed to operate in either (1)a slow chilling mode to avoid cold short- ning or(2)a rapid chilling mode for a quick turnover and reduced weight loss. The work showed that operational factors are as important as techni- cal specifications with respect to total weight loss( Gigiel et al., 1989b).Over 50%of the variance in weight loss was accounted for by the difference in time that elapsed between death and hot weighing, whilst a further 11. 8% was related to the time that elapsed between hot weighing and loading the beef side into the chiller 6.2.1.3 Product loads If specified cooling schedules are to be attained, refrigeration machinery must be designed to meet the required heat extraction rate at all times during the chilling cycle Heat enters a beef chill room via open doors, via personnel, through the insulation, from lights and cooling fans, and from the cooling carcasses or sides. The product load is the major component of he total heat to be extracted from a fully loaded chill room(Collett and Gigiel, 1986) The rate of heat release from a single side varies with time. It is at a pea immediately after loading and then falls rapidly. The peak value is primarily a function of the environmental conditions during chilling and is not sub- stantially affected by side weights in the region of 120-140kg(Kerens, 1981) In commercial systems, the peak load imposed on the refrigeration plant is so a function of the rate at which hot sides are introduced into the chill room. Increasing air velocity, decreasing air temperature or shortening loading time increases the peak heat load. There is a four-fold difference in peak load between a chill room operating at 8 C, 0.5ms loaded over &h and the same room operating at 0C, 3ms-and loaded over 2h. The average product load can easily be calculated by dividing the total enthalpy change during chilling by the chilling time. The ratios of peak to later stages of chilling, when compressor off-loading might be required eo average(Table 6.4) and actual to average heat loads (Table 6.5)can be use both to determine compressor size and ascertain the heat loads during

6.2.1.2.6 Operational factors Investigations have been carried out in a commercial chiller that was designed to operate in either (1) a slow chilling mode to avoid cold short￾ening or (2) a rapid chilling mode for a quick turnover and reduced weight loss. The work showed that operational factors are as important as techni￾cal specifications with respect to total weight loss (Gigiel et al., 1989b). Over 50% of the variance in weight loss was accounted for by the difference in time that elapsed between death and hot weighing, whilst a further 11.8% was related to the time that elapsed between hot weighing and loading the beef side into the chiller. 6.2.1.3 Product loads If specified cooling schedules are to be attained, refrigeration machinery must be designed to meet the required heat extraction rate at all times during the chilling cycle. Heat enters a beef chill room via open doors, via personnel, through the insulation, from lights and cooling fans, and from the cooling carcasses or sides. The product load is the major component of the total heat to be extracted from a fully loaded chill room (Collett and Gigiel, 1986). The rate of heat release from a single side varies with time. It is at a peak immediately after loading and then falls rapidly.The peak value is primarily a function of the environmental conditions during chilling and is not sub￾stantially affected by side weights in the region of 120–140 kg (Kerens, 1981). In commercial systems, the peak load imposed on the refrigeration plant is also a function of the rate at which hot sides are introduced into the chill room. Increasing air velocity, decreasing air temperature or shortening loading time increases the peak heat load. There is a four-fold difference in peak load between a chill room operating at 8°C, 0.5 ms-1 loaded over 8 h and the same room operating at 0 °C, 3 m s-1 and loaded over 2 h. The average product load can easily be calculated by dividing the total enthalpy change during chilling by the chilling time. The ratios of peak to average (Table 6.4) and actual to average heat loads (Table 6.5) can be used both to determine compressor size and ascertain the heat loads during the later stages of chilling, when compressor off-loading might be required. Primary chilling of red meat 107 Table 6.3 Effect of side weight on evaporative weight loss (%) after cooling for 18 and 42 h at 0 °C, 0.75 m s-1 and 95% relative humidity Chilling time Side weight (kg) (h) 50 110 130 150 170 18 2.7 2.0 1.9 1.8 1.7 42 3.6 2.5 2.4 2.2 2.1 Source: Bailey and Cox, 1976