Primary chilling of red meat 1l In beef sides the heat capacity and thickness of the carcasses makes it very difficult to reduce the internal temperature of the meat, to a value suit able for cutting or transportation, within a 24 h cooling cycle. Lamb and mutton carcasses are much smaller and rapid cooling rates can be achieved. However, it has been known for many years that reducing the temperature of the muscles in either beef or lamb to below 10.C within 10h post mortem is likely to increase the toughness of the meat when cooked owing to a phenomenon called cold shortening(see Chapter 3). Many experi- mental investigations have been carried out to determine the extent of toughening under different cooling conditions and ways of alleviating the condition by either a delay period(Anon, 1975)or electrical stimulation Crystal, 1978). In commercial operation, a chilling system needs to be designed and operated to chill efficiently while maintaining meat quali In order to achieve this objective, the designer must have information about the environmental conditions that are necessary to meet any given meat temperature specification, and the effect of these conditions on the cooling rate, weight loss, microbiology, appearance and acceptability of the product Most lamb carcasses chilled in the eu have to have a maximum inter- nal temperature of 7C, before cutting or transport. Some abattoirs would like to dispatch lamb on the day of slaughter and to meet this requirement, chilling has to be complete in 8-10h. For others overnight chilling in 14 16h is normally desired 6.2.2.1 Effect of environmental and carcass variables on cooling rate The temperature of the air and its velocity over the surface of the carcass are the two main environmental factors governing the rate that heat can be extracted from a sheep carcass. Carcass weight and fat cover control the amount of heat that has to be extracted and its rate of conduction to the surface Published data from a number of sources on chilling time is presented Table 6.8 and Table 6.9 and discussed in the following sections. 6. 2.2.1.1 Air temperature and velocity Earle and Fleming(1967) found that reducing the air temperature used during chilling from 4 to 0C results in approximately a 25% reduction in chilling time to 7C in the deep leg of carcasses ranging in weight from 12 to 33 kg No data have been located that examine the effect of air velocity on the chilling rate of lamb or mutton carcasses, but those produced for goats of 20kg(Gigiel and Creed, 1987), which have a comparable chilling time, show rge effect. In air at 0C, increasing the air velocity from 0.5 to 1ms- reduces the chilling time to 7C in the deep leg from 10 to &h and further ncreasing the velocity to 3ms" results in a time of 5h Chilling in air at 0C, 1.0ms will achieve a chilling time to 7C of 10h for carcasses up to 30kg in weight, which will allow for dispatch on the sameIn beef sides the heat capacity and thickness of the carcasses makes it very difficult to reduce the internal temperature of the meat, to a value suit￾able for cutting or transportation, within a 24h cooling cycle. Lamb and mutton carcasses are much smaller and rapid cooling rates can be achieved. However, it has been known for many years that reducing the temperature of the muscles in either beef or lamb to below 10°C within 10 h post￾mortem is likely to increase the toughness of the meat when cooked owing to a phenomenon called ‘cold shortening’ (see Chapter 3). Many experi￾mental investigations have been carried out to determine the extent of toughening under different cooling conditions and ways of alleviating the condition by either a delay period (Anon, 1975) or electrical stimulation (Crystal, 1978). In commercial operation, a chilling system needs to be designed and operated to chill efficiently while maintaining meat quality. In order to achieve this objective, the designer must have information about the environmental conditions that are necessary to meet any given meat temperature specification, and the effect of these conditions on the cooling rate, weight loss, microbiology, appearance and acceptability of the product. Most lamb carcasses chilled in the EU have to have a maximum inter￾nal temperature of 7°C, before cutting or transport. Some abattoirs would like to dispatch lamb on the day of slaughter and to meet this requirement, chilling has to be complete in 8–10h. For others overnight chilling in 14– 16 h is normally desired. 6.2.2.1 Effect of environmental and carcass variables on cooling rate The temperature of the air and its velocity over the surface of the carcass are the two main environmental factors governing the rate that heat can be extracted from a sheep carcass. Carcass weight and fat cover control the amount of heat that has to be extracted and its rate of conduction to the surface. Published data from a number of sources on chilling time is presented in Table 6.8 and Table 6.9 and discussed in the following sections. 6.2.2.1.1 Air temperature and velocity Earle and Fleming (1967) found that reducing the air temperature used during chilling from 4 to 0 °C results in approximately a 25% reduction in chilling time to 7 °C in the deep leg of carcasses ranging in weight from 12 to 33 kg. No data have been located that examine the effect of air velocity on the chilling rate of lamb or mutton carcasses, but those produced for goats of 20 kg (Gigiel and Creed, 1987), which have a comparable chilling time, show a large effect. In air at 0 °C, increasing the air velocity from 0.5 to 1m s-1 reduces the chilling time to 7 °C in the deep leg from 10 to 8 h and further increasing the velocity to 3 m s-1 results in a time of 5 h. Chilling in air at 0 °C, 1.0 m s-1 will achieve a chilling time to 7 °C of 10 h for carcasses up to 30 kg in weight, which will allow for dispatch on the same Primary chilling of red meat 111