16 Secondary chilling of meat and meat products Meat is chilled immediately after slaughter. Most of the subsequent opera- tions in the cold chain are designed to maintain the temperature of the meat Cooking is a very common operation in the production of many meat products and operators appreciate the importance of rapidly cooling the cooked product. However, any handling such as cutting, mixing or tumbling will add heat to the meat and increase its temperature. A secondary cooling operation is always required with chilled meat and meat products to reduce their temperature to approaching 0C and maintain their storage life The aim of any cooking process for meat/meat produce is to ensure the destruction of vegetative stages of any pathogenic microorganisms. However, there is always the possibility that the cooking process will not kill some microorganisms that produce spores or that the food can become recontaminated. Therefore, microbiologists recommend that the tempera ture of the meat should be rapidly reduced, especially from approximately 60 and 5C, to prevent multiplication of existing or contaminating bacte ria. Rapid cooling is also desirable with cooked products to maintain quality by eliminating the overcooking that occurs during slow cooling There are specific cooling recommendations for cook-chill and cook-freeze catering systems. However, even with thin products these are difficult to achieve without surface freezing. Cooling large hams and other cooked meat joints is inherently a much slower process and studies have shown that companies often have very poor cooling systems. The methods available to cool meat joints, pies and other cooked prod ucts have been described in detail by James(1990a). A review of the use of vacuum cooling in the food industry has been published by McDonald and Sun(2000)
16 Secondary chilling of meat and meat products Meat is chilled immediately after slaughter. Most of the subsequent operations in the cold chain are designed to maintain the temperature of the meat. Cooking is a very common operation in the production of many meat products and operators appreciate the importance of rapidly cooling the cooked product. However, any handling such as cutting, mixing or tumbling will add heat to the meat and increase its temperature. A secondary cooling operation is always required with chilled meat and meat products to reduce their temperature to approaching 0 °C and maintain their storage life. The aim of any cooking process for meat/meat produce is to ensure the destruction of vegetative stages of any pathogenic microorganisms. However, there is always the possibility that the cooking process will not kill some microorganisms that produce spores or that the food can become recontaminated. Therefore, microbiologists recommend that the temperature of the meat should be rapidly reduced, especially from approximately 60 and 5 °C, to prevent multiplication of existing or contaminating bacteria. Rapid cooling is also desirable with cooked products to maintain quality by eliminating the overcooking that occurs during slow cooling. There are specific cooling recommendations for cook–chill and cook–freeze catering systems. However, even with thin products these are difficult to achieve without surface freezing. Cooling large hams and other cooked meat joints is inherently a much slower process and studies have shown that companies often have very poor cooling systems. The methods available to cool meat joints, pies and other cooked products have been described in detail by James (1990a). A review of the use of vacuum cooling in the food industry has been published by McDonald and Sun (2000)
322 Meat refrigeration The majority of plants rely on air blast cooling systems for the chilling of pre-cooked meat products. In batch systems the products, packs or tray of cooked material are placed directly on racks in the chiller or on trolleys that can be wheeled into the chiller when fully loaded. Continuous systems range from trolleys pulled through tunnels to conveyorised spiral or tunnel Some meals and products are chilled using cryogenic tunnels, however, care must be taken to avoid surface freezing. Imperviously packed prod- ucts can be chilled by immersion in cooled water or other suitable liquid. With some cooked products such as large hams in moulds and sausages, chlorinated water sprays can be used in the initial stages of cooling Increas ingly, pie fillings are pressure-cooked and vacuum cooled. With many prod ucts an initial cooling stage using ambient air can often substantially reduce the cooling load in the cooling system 16.1 Cooked meat 16.1.1 Legislation In the UK the Food Safety (Temperature Control) Regulations(1995 apply to any food that "is likely to support pathogenic micro-organisms or the formation of toxins'and that must be kept at or below 8C. Regulation 11 does not define a cooling time or rate, only that the food should be cooled as quickly as possible following the final heating stage The guidance document to the above regulations produced by the Department of Health is even less specific Under heading Vill, cooling of food, paragraph 47 it states: The cooling period for any food would not be regarded as unacceptable merely because other equipment, not present at he business, could have cooled the food more quickly. The time taken to chieve cooling must be consistent with food safety. Cooling will often be a step which is critical to food safety The Meat Products(Hygiene) Regulations(1994)contain special condi tions for meat-based prepared meals. They require that the meat product and the prepared meal shall be refrigerated to an internal temperature of +10C or less within a period of not more than 2h after the end of cooking However, they then go on to state that produce may be exempt from the 2h period where a longer period is justified for reasons connected with the production technology employed. The wording is similar in the EC Meat recurve In the USa the essential rules of the US Regulations(318. 179 CFR CH Il, 1.1.96 edition) on safe cooling of cooked meats are Chilling shall begin within 90 min after the cooking cycle is completed All products should be chilled from 488C to 12. 7C in no more than
The majority of plants rely on air blast cooling systems for the chilling of pre-cooked meat products. In batch systems the products, packs or trays of cooked material are placed directly on racks in the chiller or on trolleys that can be wheeled into the chiller when fully loaded. Continuous systems range from trolleys pulled through tunnels to conveyorised spiral or tunnel air blast chillers. Some meals and products are chilled using cryogenic tunnels, however, care must be taken to avoid surface freezing. Imperviously packed products can be chilled by immersion in cooled water or other suitable liquid. With some cooked products such as large hams in moulds and sausages, chlorinated water sprays can be used in the initial stages of cooling. Increasingly, pie fillings are pressure-cooked and vacuum cooled. With many products an initial cooling stage using ambient air can often substantially reduce the cooling load in the cooling system. 16.1 Cooked meat 16.1.1 Legislation In the UK the Food Safety (Temperature Control) Regulations (1995) apply to any food that ‘is likely to support pathogenic micro-organisms or the formation of toxins’ and that must be kept at or below 8 °C. Regulation 11 does not define a cooling time or rate, only that the food should be cooled as quickly as possible following the final heating stage. The guidance document to the above regulations produced by the Department of Health is even less specific. Under heading VIII, cooling of food, paragraph 47 it states: ‘The cooling period for any food would not be regarded as unacceptable merely because other equipment, not present at the business, could have cooled the food more quickly. The time taken to achieve cooling must be consistent with food safety. Cooling will often be a step which is critical to food safety’. The Meat Products (Hygiene) Regulations (1994) contain special conditions for meat-based prepared meals. They require that the meat product and the prepared meal shall be refrigerated to an internal temperature of +10 °C or less within a period of not more than 2 h after the end of cooking. However, they then go on to state that produce may be exempt from the 2 h period where a longer period is justified for reasons connected with the production technology employed. The wording is similar in the EC Meat Products Directive. In the USA the essential rules of the US Regulations (318.17 9 CFR CH III, 1.1.96 edition) on safe cooling of cooked meats are: • Chilling shall begin within 90 min after the cooking cycle is completed. • All products should be chilled from 48.8 °C to 12.7 °C in no more than 6 h. 322 Meat refrigeration
Secondary chilling of meat and meat products 323 able 16.1 Recommended good practice and maximum cooling times for uncured meat Cooling time(h) Good practice Maximi To50°C From50°to12°C From12°to5°C 1618 Total time to5°C Source: Gaze et al.. 1998 able 16.2 Recommended good practice and maximum cooling times for cured meat Cooling time(h) Good practice Maximi To50°C From50°to12°C From12°to5°C 1.75 Total time to5°C 10.00 12.50 Source: Gaze et al.. 1998 Chilling shall continue and the product should not be packed for ship ment until it has reached 4. 4C These US Federal Regulations have been widely adopted outside areas under the control of the USDA, including by European retailers. Further recommendations have been made by Gaze et aL., 1998. Their main recom ' For a typical uncured cooked meat product, made from good quality raw material under hygienic conditions and with sound process controls, it is suggested that the following limitations (Table 16.1) for cooling time from completion of the cooking process should apply For products which are cured(defined as minimum 2.5% salt on water phase and 100 ppm nitrite in-going), these times may be extended (Table 16.2). As an approximation it is suggested this be by 25%. 16.1.2 Practical In many industrial cooking operations whole hams and large meat joints are often cooked and cooled in an intact form and then supplied to restau- rants or retail shops where they are sliced before sale. Surveys(Cook, 1985: James, 1990b and c; Gaze et al., 1998) have shown that industry uses a variety of methods for cooling whole hams(Table 16.3, Table 16.4 and Table 16.5) In these processes the earlier data showed that cooling times were as long
• Chilling shall continue and the product should not be packed for shipment until it has reached 4.4 °C. These US Federal Regulations have been widely adopted outside areas under the control of the USDA, including by European retailers. Further recommendations have been made by Gaze et al., 1998. Their main recommendations are that: • ‘For a typical uncured cooked meat product, made from good quality raw material under hygienic conditions and with sound process controls, it is suggested that the following limitations (Table 16.1) for cooling time from completion of the cooking process should apply.’ • ‘For products which are cured (defined as minimum 2.5% salt on water phase and 100 ppm nitrite in-going), these times may be extended (Table 16.2). As an approximation it is suggested this be by 25%.’ 16.1.2 Practical In many industrial cooking operations whole hams and large meat joints are often cooked and cooled in an intact form and then supplied to restaurants or retail shops where they are sliced before sale. Surveys (Cook, 1985; James, 1990b and c; Gaze et al., 1998) have shown that industry uses a variety of methods for cooling whole hams (Table 16.3, Table 16.4 and Table 16.5). In these processes the earlier data showed that cooling times were as long Secondary chilling of meat and meat products 323 Table 16.1 Recommended good practice and maximum cooling times for uncured meat Cooling time (h) Good practice Maximum To 50 °C 1 2.5 From 50 °C to 12 °C 6 6 From 12 °C to 5 °C 1 1.5 Total time to 5 °C 8 10 Source: Gaze et al., 1998. Table 16.2 Recommended good practice and maximum cooling times for cured meat Cooling time (h) Good practice Maximum To 50 °C 1.25 3.25 From 50 °C to 12 °C 7.5 7.5 From 12 °C to 5 °C 1.25 1.75 Total time to 5 °C 10.00 12.50 Source: Gaze et al., 1998
324 Meat refrigeration Table 16.3 Examples of commercial ham cooling in the UK Cooling method 动品 Total Final rature° In metal mould in chill oom17to6°C,0.2ms In bag in chill room -3°Cto-10°0.3ms In bag water shower then chill room at-1°then 3°Cto5°C In bag in ambient 13.5 15°Cto7°C Source: James, 1990c later study cooling times were still as long as 16h but final temperatur.e as 21h, and final temperatures high: 15-20C(Table 16.3, Table 16.4). In the were no higher than 8C (Table 16.6) A similar picture is seen in data on the cooling of cooked pork with final mperatures as high as 12C and cooling times of up to 20h(Table 16.4) Corresponding figures for the cooling of cooked beef were 15C and 22h (Table 16.4). Data obtained from numerous sources within the UK cater- ing industry by Mottishaw(1986)indicate that the cooling procedures for bulk-cooked meats could also vary considerably(Table 16.6). For example, some meat products are said to be cooled to 1C in 2h, whereas at the other extreme, products may take 72h to cool to 4 C. Commonly, a 4.5kg product ill take 12h to cool below 5C and larger products could take longer. In ddition, there is often a delay before chilling begins, this may vary from 10 min up to 6h 16.1.3 Experimental studies The most relevant cooling data for cooling of cooked meat from laboratory investigations are shown in Table 16.7. A simple process for estimating the immersion cooling time of beef roasts has been produced by Nolan (1986). Generally, the results show that immersion cooling is almost twice as fast as air cooling at the same temperature. Vacuum cooling was an order of magnitude faster than immersion cooling but the weight loss was substantially (over twice) higher. Using a less severe vacuum treatment or a combination of the different methods is likely to provide an optim solution The James and Bailey(1982) study showed that in ham cooling, a 0. 75h initial cooling period in ambient air reduced the initial load on the refrig- eration by a factor of almost 2. If the ham was placed straight into air at
as 21 h, and final temperatures high: 15–20 °C (Table 16.3,Table 16.4). In the later study cooling times were still as long as 16 h but final temperatures were no higher than 8 °C (Table 16.6). A similar picture is seen in data on the cooling of cooked pork with final temperatures as high as 12 °C and cooling times of up to 20 h (Table 16.4). Corresponding figures for the cooling of cooked beef were 15 °C and 22 h (Table 16.4). Data obtained from numerous sources within the UK catering industry by Mottishaw (1986) indicate that the cooling procedures for bulk-cooked meats could also vary considerably (Table 16.6). For example, some meat products are said to be cooled to 1 °C in 2 h, whereas at the other extreme, products may take 72 h to cool to 4 °C. Commonly, a 4.5 kg product will take 12 h to cool below 5 °C and larger products could take longer. In addition, there is often a delay before chilling begins, this may vary from 10 min up to 6 h. 16.1.3 Experimental studies The most relevant cooling data for cooling of cooked meat from laboratory investigations are shown in Table 16.7. A simple process for estimating the immersion cooling time of beef roasts has been produced by Nolan (1986). Generally, the results show that immersion cooling is almost twice as fast as air cooling at the same temperature.Vacuum cooling was an order of magnitude faster than immersion cooling but the weight loss was substantially (over twice) higher. Using a less severe vacuum treatment or a combination of the different methods is likely to provide an optimum solution. The James and Bailey (1982) study showed that in ham cooling, a 0.75 h initial cooling period in ambient air reduced the initial load on the refrigeration by a factor of almost 2. If the ham was placed straight into air at 324 Meat refrigeration Table 16.3 Examples of commercial ham cooling in the UK Cooling method Weight Height Cooling Total Final (kg) of joint time to (h) temperature (°C) (cm) 20 °C (h) In metal mould in chill 6.4 19 12 1.4 15 room 17 °C to 6 °C, 0.2 ms-1 In bag in chill room 7.3 18 9.3 21 2 -3 °C to -10 °C, 0.3 ms-1 In bag water shower then 6.8 18 6.6 14 5 chill room at -1 °C then 3 °C to 5 °C In bag in ambient 6.8 20 – 13.5 24 15 °C to 7 °C Source: James, 1990c
Table 16.4 Previously unpublished survey data on cooling of cooked meat in industry and shops Meat Wt Diam mm Method rap Initial Time(h) 10C Final temp/time g Cto50°C Ham 6.35 Chill roon176°C0.2ms Metal mould 15/14 3.8 726 Chill room -3/-1oC03ms- Sealed bag 3.8 4 Chill room 17-6. 0.2 ms- Sealed bag 0.0 Shop air 15-7C<0.2ms Sealed ba -055 4.7 9/21 4/13.5 1/13.5 4.7 22/13.5 Shower 20min. chill 3/5C 4h Sealed bas ∽8 9.3 5/14 Bacon 4.54 114 Factory air, 20-12C 4/12.5 114 2.6 15/13.5 114 16/13.5 Pork 6.80 Shower 20min, chill-1C 4h, chill 3/5C Bag 5/1 5/12 p30-20°C7h,chil86°C 20476-101 Kitchen22°c2h,chil2/5°C Uncovered 4/7.5 2.0476-101 4/9.0 Beef5.9016 Kitchen23°C1.5h,chil3-5° Netted 9/15 Chil200° Netted 2.6 11.0 Shop30-20°c7h, chill 186°C Punctured 15/2 101 Blast chill -5/-3C 1.2 ms Uncovered 713.9 3.86 127 Blast chill 4/5C 2 ms Netted 3.40 127 Domestic fridge 2/7C static Netted 3.40 Chil1/2°C0.3ms Netted 3.63 Blast freeze" ms- Netted 1.6 4. 9/48
Secondary chilling of meat and meat products 325 Table 16.4 Previously unpublished survey data on cooling of cooked meat in industry and shops Meat Wt Diam mm Method Wrap Initial Time (h) 10 °C Final temp/time kg temp °C to 50 °C Ham 6.35 191 Chill room 17–6 °C 0.2 ms-1 Metal mould 71 3.6 – 15/14 70 3.8 – 15/14 7.26 178 Chill room -3/-1 °C 0.3 ms-1 Sealed bag 69 3.8 12.7 2/21 68 3.4 12.5 2/21 Chill room 17–6 °C 0.2 ms-1 Sealed bag – 4.8 20.0 9/21 – 4.7 20.0 9/21 6.80 203 Shop air 15–7 °C <0.2 ms-1 Sealed bag 69 3.7 – 24/13.5 75 4.2 – 21/13.5 75 4.7 – 23/13.5 75 4.3 – 22/13.5 6.80 178 Shower 20 min, chill 3/5 °C 4 h Sealed bag 72 2.6 9.3 5/14 Bacon 4.54 114 Factory air, 20–12 °C Bag 76 1.9 – 14/12.5 4.08 114 71 2.6 – 15/13.5 4.08 114 76 2.7 – 16/13.5 Pork 6.80 203 Shower 20 min, chill -1 °C 4 h, chill 3/5 °C Bag 77 2.2 6.8 5/12 6.35 203 79 2.2 7.2 5/12 5.44 165 Shop 30–20 °C 7 h, chill 18–6 °C Bag 82 4.5 19.5 12/20 2.04 76–101 Kitchen 22 °C 2 h, chill 2/5 °C Uncovered 100 2.0 5.9 4/7.5 2.04 76–101 100 1.9 5.5 4/9.0 Beef 5.90 165 Kitchen 23 °C 1.5 h, chill 13–5 °C Netted 93 2.4 13.0 9/15 6.80 152 Chill 20–0 °C Netted 70 2.6 11.0 0/16 5.90 165 Shop 30–20 °C 7 h, chill 18–6 °C Punctured 75 4.4 22.0 15/22 bag – 101 Blast chill -5/-3 °C 1.2 ms-1 Uncovered 90 – 3.4 7/3.9 3.86 127 Blast chill 4/5 °C 2 ms-1 Netted 73 1.7 5.3 5/7 3.40 127 Domestic fridge 2/7 °C static Netted 72 2.2 7.5 9/7 3.40 127 Chill 1/2 °C 0.3 ms-1 Netted 71 1.9 6.8 9/7 3.63 127 Blast freeze -30 °C 1 ms-1 Netted 73 1.6 4.6 9/4.8
326 Meat refrigeration Table 16.5 Examples of commercial ham cooling in the UK Cooling method Cooling time(h) Temperature Total To10°C Initial In casings and moulds in batch air chillers at -1°C,0.93ms ngs and moulds in forced air at O°C Dry cured hams in conveyorised system using refrigerated bri Premium hams in conveyorised stem using refrigerated brine Rind-on hams in conveyorised Chill room with moderate air movement In static air in a refrigerator 10.5 Revision of above Immersion in ambient water followed by moving air Source: CCFRA survey., 1995. Interpolated data from cooling plots Table 16.6 Summary of previously unpublished survey data on cooling of cooked meat in industry and shops joint size Time(h) Time(h)to Temp(C) Time(h) 5.44-7.26kg,178mm 11.4 15.6 diameter 0.9/3546/176 363-4.54kg,114mm diameter 1/1.7 2.3/5.3 4/13.5 1.81-2. kg, 76mm Average 1.5 diameter Microbiologically acceptable: 5h 50-10C, 12h 10-1 -2C it released 220 Wh in the first hour compared with 118 Wh after 0.75 min in ambient air. In this case a period of ambient cooling would sub- stantially reduce the peak heat load on the refrigeration system. Alterna tive methods of cooling are also available. a double cabinet cryogenic batch cooler has been used to cool cooked roast, smoked pork loin and smoked ham from 65C to below 10C with a weight loss of >0.5%
-2 °C it released 220 Wh in the first hour compared with 118 Wh after 0.75 min in ambient air. In this case a period of ambient cooling would substantially reduce the peak heat load on the refrigeration system. Alternative methods of cooling are also available.A double cabinet cryogenic batch cooler has been used to cool cooked roast, smoked pork loin and smoked ham from 65 °C to below 10 °C with a weight loss of >0.5%. 326 Meat refrigeration Table 16.5 Examples of commercial ham cooling in the UK Cooling method Cooling time (h) Temperature (°C) Total To 10 °C Initial Final In casings and moulds in 16 7 65 4 batch air chillers at -1 °C, 0.93 ms-1 In casings and moulds in 8 70 3 forced air at 0 °C Dry cured hams in conveyorised 10 6 75 3 system using refrigerated brine Premium hams in conveyorised 14 6 75 3 system using refrigerated brine Rind-on hams in conveyorised 8 5.5 75 5 system using refrigerated brine Chill room with moderate air 5 3.5 73 3 movement In static air in a refrigerator 15 10.5 80 8 Revision of above. Immersion 8 5 78 0 in ambient water followed by moving air Source: CCFRA survey, 1995. Interpolated data from cooling plots. Table 16.6 Summary of previously unpublished survey data on cooling of cooked meat in industry and shops Joint size Time (h) Time (h) to Temp (°C) Time (h) to 60 °C 50–10 °C 5.44–7.26 kg, 178 mm Average 2.4 10.6 11.4 15.6 diameter Range 0.9/3.5 4.6/17.6 2/24 12/22 3.63–4.54 kg, 114 mm Average 1.4 3.8 10.5 8.6 diameter Range 1/1.7 2.3/5.3 5/15 4/13.5 1.81–2.27 kg, 76 mm Average 1.5 3.7 4 8.3 diameter Microbiologically acceptable: 5 h 50–10 °C, 12 h 10–1 °C
Secondary chilling of meat and meat products 327 Table 16.7 Cooling times(h) for meat joints from published sources Ref. Cooling regime 70=50°50-12°12-5°70-5°708°C Good practice 1.5 13.75 kg vacuum packed beef roasts330×160×130mm Vacuum 1.4 0.9 2.1 Immersion1±1°C Air1±1 Air1±1°C,1 8 669 7.2 0.75h at 15C then". 5ms- 3.0 3 5-5.5kg(11-12Ib)ham logs 400×120×120 mm in metal oulds 18°C 2.1 then air0°C,3ms-1 air0°C.3ms- botton 0.94 kg beef slabs. 50mm thick Air0°C,12ms Water0°C Vacuum 2.7kg rolled beef forequarter Air0°C,1.2ms-l 0 2.7 kg rolled beef silverside 110mm dia Air0°C,1.2ms-l 3.1 Vacuum .7 6.4kg boned out turkey Air0°C,1.2ms Water0° Vacuum 7.1 kg boned Water0°C Sources: 1. McDonald et al.(2000); 2. James and Bailey (1982): 3. Anon(1987): 4. Burfoot eral!.(1990
Secondary chilling of meat and meat products 327 Table 16.7 Cooling times (h) for meat joints from published sources Ref. Cooling regime 70–50 °C 50–12 °C 12–5 °C 70–5 °C 70–8 °C Good practice 1 6 1 8 Maximum 2.5 6 1.5 10 1 3.75 kg vacuum packed beef roasts 330 ¥ 160 ¥ 130 mm Vacuum 0.1 1.4 0.9 2.4 2.1 Immersion 1 ± 1 °C 1.5 4.2 2.8 8.5 6.9 Air 1 ± 1 °C, 2 ms-1 1.2 3.5 2.9 7.6 6.1 Air 1 ± 1 °C, 1 ms-1 1.5 4.2 4.6 10.3 8.1 2 7 kg hams in metal moulds Air -2 °C, 5 ms-1 2.4 3.8 2.6 9.0 7.2 0.75 h at 15 °C then -2 °C, 5 ms-1 3.0 4.0 2.9 9.9 7.9 3 5–5.5 kg (11–12 lb) ham logs 400 ¥ 120 ¥ 120 mm in metal moulds 30 m water spray at 18 °C 0.6 4.0 2.1 6.7 6.0 then air 0 °C, 3 ms-1 top rack 30 m water spray at 18 °C then 0.4 3.9 2.2 6.5 5.5 air 0 °C, 3 ms-1 bottom rack 4 0.94 kg beef slabs, 50 mm thick 50–10 °C 70–10 °C Air 0 °C, 1.2 ms-1 1.7 2.1 Water 0 °C 1.0 1.2 Vacuum 0.6 0.6 2.7 kg rolled beef forequarter, 110 mm dia. Air 0 °C, 1.2 ms-1 4.4 5.1 Water 0 °C 3.1 3.6 Vacuum 0.3 0.4 2.7 kg rolled beef silverside, 110 mm dia. Air 0 °C, 1.2 ms-1 4.0 4.9 Water 0 °C 2.6 3.1 Vacuum 0.6 0.7 6.4 kg boned out turkey Air 0 °C, 1.2 ms-1 5.4 6.6 Water 0 °C 4.6 5.6 Vacuum 0.2 0.3 7.1 kg boned out ham Air 0 °C, 1.2 ms-1 8.9 10.4 Water 0 °C 4.8 5.9 Vacuum 0.5 0.5 Sources: 1. McDonald et al. (2000); 2. James and Bailey (1982); 3. Anon (1987); 4. Burfoot et al. (1990)
328 Meat refrigeration 16.2 Pastry products 16.2.1 Commercial operations Although it should be a far simpler and quicker operation to reduce the temperature of small individual items, such as meat pies, many manufac turers allow an inadequate length of time for the cooling operation and the products are packaged at temperatures substantially above the storage value. After wrapping and boxing it is very difficult to remove the residual heat. Typically, pie manufacturers allow Ih for their single-stage cooling operations and the core temperature of pies before packing can range from 17to37°C(able16.8) The surface temperature of cooked products is very high when they leave baking ovens and consequently the difference between the surface and the ambient is very large at this time. To reduce energy usage and costs a number of manufacturers operate two-stage cooling operations utilising ambientairfollowedbysubzeroairinthesecondstage(table16.10).com paring the data from the first two examples in Table 16.9 and Table 16.10 it can be seen that similar final product temperatures are produced in the ingle- and two-stage cooling processes. The use of very low temperatures during single-stage cooling operations can produce quality problems due to freezing of the pastry at the surface of the products. In addition with some baked products manufacturers believe that the quality of the pastry suffers if taken below 10C. One minced beef pie manufacturer used air at 12Cin he second stage of a two-stage cooling process to avoid this problem(Table 16.10). However, even when the cooling time was increased by 25%, the ature of the pie was 20C at the packing stage. In two facto large pies(4.5kg) were also produced for catering use or to be sold after Table 16.8 Examples of commercial single-stage cooling of pastry products in the uK Product Type of Air Cooling Temperature Temp. Velocity (h) Initial Final (°C)(ms-2) (°C)(°C) Steak and kidney Spiral 11/170.5 90-9517-20 pie(185g Spiral 90-9517-20 Cold store 1.090-9530 Ambient 1.0 90-9537 Ambient 1.090-9532 Spiral 11/17 355 0.8939610 Pork pie(4.5 kg) Ambient 16-23 Source: James, 1990c
16.2 Pastry products 16.2.1 Commercial operations Although it should be a far simpler and quicker operation to reduce the temperature of small individual items, such as meat pies, many manufacturers allow an inadequate length of time for the cooling operation and the products are packaged at temperatures substantially above the storage value. After wrapping and boxing it is very difficult to remove the residual heat. Typically, pie manufacturers allow 1 h for their single-stage cooling operations and the core temperature of pies before packing can range from 17 to 37 °C (Table 16.8). The surface temperature of cooked products is very high when they leave baking ovens and consequently the difference between the surface and the ambient is very large at this time. To reduce energy usage and costs a number of manufacturers operate two-stage cooling operations utilising ambient air followed by sub zero air in the second stage (Table 16.10). Comparing the data from the first two examples in Table 16.9 and Table 16.10 it can be seen that similar final product temperatures are produced in the single- and two-stage cooling processes. The use of very low temperatures during single-stage cooling operations can produce quality problems due to freezing of the pastry at the surface of the products. In addition with some baked products manufacturers believe that the quality of the pastry suffers if taken below 10 °C. One minced beef pie manufacturer used air at 12 °C in the second stage of a two-stage cooling process to avoid this problem (Table 16.10). However, even when the cooling time was increased by 25%, the core temperature of the pie was 20 °C at the packing stage. In two factories, large pies (4.5 kg) were also produced for catering use or to be sold after 328 Meat refrigeration Table 16.8 Examples of commercial single-stage cooling of pastry products in the UK Product Type of Air Cooling Temperature chiller Temp. Velocity time Initial Final (°C) (ms-1 ) (h) (°C) (°C) Steak and kidney Spiral -11/-17 0.5 1.0 90–95 17–20 pie (185 g) ≤ Spiral -3 3–5 1.0 90–95 17–20 ≤ Cold store -30 <0.2 1.0 90–95 30 ≤ Ambient 20 0.3 1.0 90–95 37 ≤ Ambient 20 3.5 1.0 90–95 32 Sausage rolls Spiral -11/-17 0.5 0.8 93–96 10 Pork pie (4.5 kg) Ambient 16–23 <0.2 8.0 68 25 Source: James, 1990c
Secondary chilling of meat and meat products 329 Table 16.9 Examples of commercial two-stage cooling of pastry products in the Product vpe of Cooling Temperature Temp. Veloci )(C) Ambient kidne 0.67 mbient 3-5 0.3-1.4 Ambient Minced beef ie(140g) (45kg) Amb 6.0ms-)appreciable reduc- tions in cooling time were still being achieved. In a high throughput baking line(>1000 items per hour) the 7% increase in throughput, which would be achieved by raising the air velocity from 6 to 10ms and consequently reducing the cooling time by 10 min, could justify the higher capital and Inning costs of larger fans. With larger pies cooling times of up to 6h have been measured(Fig. 16.2). Only one reference(McDonald and Sun, 2000) to the vacuum cooling of pork pies has been located. This quotes a coolin time for 0.5kg pies from 80 to 10C of over &h
slicing from delicatessen outlets. In a single-stage ambient cooling operation the centre temperature was still 25 °C (Table 16.8) after 8 h; however in the two-stage process the centre of the pie had been reduced to 10 °C after 6.5 h (Table 16.9). 16.2.2 Experimental studies Data from the most relevant experimental studies on pie cooling are shown in Table 16.10. The importance of achieving a minimum required air velocity around small products was clearly demonstrated by data obtained from cooling pork pies (Fig. 16.1).To guarantee that all the crust remained above -2 °C on the unwrapped 400 g (70 mm high, 95 mm diameter) pies an air temperature of -1.5–±0.5 °C was used. At this temperature a small increase in air velocity from 0.5 to 1.0 ms-1 reduced the cooling time by 85 min (almost 30%). Even at very high velocities (>6.0 ms-1 ) appreciable reductions in cooling time were still being achieved. In a high throughput baking line (>1000 items per hour) the 7% increase in throughput, which would be achieved by raising the air velocity from 6 to 10 ms-1 and consequently reducing the cooling time by 10 min, could justify the higher capital and running costs of larger fans. With larger pies cooling times of up to 6 h have been measured (Fig. 16.2). Only one reference (McDonald and Sun, 2000) to the vacuum cooling of pork pies has been located. This quotes a cooling time for 0.5 kg pies from 80 to 10 °C of over 8 h. Secondary chilling of meat and meat products 329 Table 16.9 Examples of commercial two-stage cooling of pastry products in the UK Product Type of Air Cooling Temperature chiller Temp. Velocity time Initial Final (°C) (ms-1 ) (h) (°C) (°C) Steak and Ambient 20 3–5 0.33 93 – kidney pie (185 g) Spiral -3 2 0.67 – 17–20 ≤ Ambient 20 3–5 0.33 93 – Spiral -3 0.3–1.4 0.67 – 22 ≤ Ambient 20 0.3 0.33 93 – Spiral -3 2 0.67 – 24–27 Minced beef Ambient 20 <0.2 0.16 96 80 pie (140 g) Chill room 12 1 1.08 80 20 Gala pie Ambient 20 <0.2 1.75 96 76 (4.5 kg) Chill room 0 <0.4 6.5 76 10 Source: James, 1990c
330 Meat refrigeration Table 16.10 Published data on the cooling of pork pies Reference Pie weight Conditions Time to 5°C(h) 1&2 0° C still air for60 min jelly then7°C til centre at10° C then-20°C,0.5ms1 0C still air for 60 min jelly then 10°C.5ms o° still air for6 Omin jelly then-20°C 1.6 20° still air for60 min jelly then1°C 0C still air for 70 min jelly then -30C, sPams" for 63 min jelly then"C, 2.6 1°C.3ms -1°C.3ms -1 45017°C,2ms-for38 min then-1.5°C, 4ms-1 17°C,2ms-for38 min then-15°C 2.9 101 17°C,2ms-for38 min then-4°C 4 ms-I 17°C,2 ms- for38 min then-1.5°C, 2.6 10 17°C,2ms-lfor38 min then-10°, 17°C,2ms-lfor38 min then-10°C, 17°C.2 ms-I for38 min then-1.5°C 4.6 17°C.2 ms for38 min then-15°C 1 ms 17°C.2 ms for38 min then-15°C 17°C,2 ms for38 min then-1.5°C, 2.6 Sources: 1. Evans Gigiel(1989a): 2. Evans Gigiel(1989b): 3. James(1990b); 4. James era.(1987);5. James(1990c) 16.3 Solid/liquid mixtures Meat slurries, mixtures of solid meat and a gravy/sauce are commonly used as pie/pasty fillings and a growing range of ready meals. Surveys have shown that many companies have problems in cooling meat slurries(Table 16.11) and in the centre of large vats of pie fillings, for example, cooling rates can be as slow as 2C per hour. Subsequent laboratory studies showed that large
16.3 Solid/liquid mixtures Meat slurries, mixtures of solid meat and a gravy/sauce are commonly used as pie/pasty fillings and a growing range of ready meals. Surveys have shown that many companies have problems in cooling meat slurries (Table 16.11) and in the centre of large vats of pie fillings, for example, cooling rates can be as slow as 2 °C per hour. Subsequent laboratory studies showed that large 330 Meat refrigeration Table 16.10 Published data on the cooling of pork pies Reference Pie weight Conditions Time to (g) 5 °C (h) 1 & 2 75 20 °C still air for 60 min jelly then 7 °C 3.0 until centre at 10 °C then -20 °C, 0.5 ms-1 20 °C still air for 60 min jelly then 1.5 -10 °C, 5 ms-1 20 °C still air for 60 min jelly then -20 °C, 1.6 0.5 ms-1 20 °C still air for 60 min jelly then 1 °C, 2.3 0.5 ms-1 20 °C still air for 70 min jelly then -30 °C, 2.9 5 ms-1 0 °C, 3 ms-1 for 63 min jelly then -30 °C, 2.6 5 ms-1 3 235 -1 °C, 3 ms-1 1.5 450 -1 °C, 3 ms-1 >2.5 900 -1 °C, 3 ms-1 >6 4 450 17 °C, 2 ms-1 for 38 min then -1.5 °C, 3.2 4 ms-1 17 °C, 2 ms-1 for 38 min then -1.5 °C, 2.9 10 ms-1 17 °C, 2 ms-1 for 38 min then -4 °C, 3.0 4 ms-1 17 °C, 2 ms-1 for 38 min then -1.5 °C, 2.6 10 ms-1 17 °C, 2 ms-1 for 38 min then -10 °C, 2.5 4 ms-1 17 °C, 2 ms-1 for 38 min then -10 °C, 2.2 10 ms-1 5 450 17 °C, 2 ms-1 for 38 min then -1.5 °C, 4.6 0.5 ms-1 17 °C, 2 ms-1 for 38 min then -1.5 °C, 3.6 1 ms-1 17 °C, 2 ms-1 for 38 min then -1.5 °C, 2.9 6 ms-1 17 °C, 2 ms-1 for 38 min then -1.5 °C, 2.6 10 ms-1 Sources: 1. Evans & Gigiel (1989a); 2. Evans & Gigiel (1989b); 3. James (1990b); 4. James et al. (1987); 5. James (1990c)
