The refrigeration of chilled foods 83 in the atmosphere by, particularly, carbon dioxide and water vapour. Fears of excessive global climate change are associated with high emissions of carbon dioxide(mainly from burning fossil fuels in power stations and elsewhere)and of other more powerful but much less abundant 'greenhouse gases including HFCs(hydrofluorocarbons) Under the auspices of the Montreal Protocol(Anon. 1987), the developed world ceased the production of ozone-depleting CFCs during the 1990s. This was made possible by the substitution of less environmentally harmful HCFCs The HCFCs themselves are expected to be phased out by 2010-20, if not earlier and in some applications there are no known effective substitutes at present available In Europe, the use of CFCs in existing equipment will be banned, and the supply of new equipment using HCFCs will be prohibited. At the time of writing. dates for these limitations are still uncertain. These matters have two direct impacts on users of chilling equipment. Firstly, every change of technology costs money, and may in some cases result in an increase in running costs as well as re-equipment costs. Secondly, it may be necessary in the future to move from locally safe but globally harmful CFCs and HCFCs to globally safe but potentially locally hazardous substances such as ammonia and propane. These latter substances can be used safely, but there are added costs and added needs for proper training of equipment users. HFCs(hydrofluoro- carbons) have been developed as alternatives. These do not deplete ozone and are widely available, but are being targeted by some environmentalists, as they are greenhouse gases within the Kyoto Protocol The purchaser of equipment needs to be aware of these matters, as he may otherwise obtain machinery that will have to be modified or even replaced long before its expected economic life is over. There could also be financial implications at the time of machinery disposal. The reduction of CFC and HCFC use in insulating foams in storage cabinets and stores has been well publicised but at the time of writing the implications for refrigeration machiner fficiently widely appreciated A further related issue is the relation between global warming, energy nd energy efficiency. New refrigerant fluids may be less efficient, but future environmental concerns may penalise excessive energy use. The equipment specifier is likely to face some difficult choices over the next few years. The user will face new responsibilities for minimising refrigerant leakage, ensuring fficient operation, and using only properly qualified maintenance staff. For a fuller discussion see(Heap 1998) 4.5 Chiled foods and refrigeration The benefit of chilled storage is the extension of life of the foodstuff in good condition, by slowing down the rate of deterioration. Chilling, it must be emphasised, cannot improve the quality of a poor product, neither can it stop the processes of spoilage- it can only slow them down(see Chapters 7, 9, 10)
in the atmosphere by, particularly, carbon dioxide and water vapour. Fears of excessive global climate change are associated with high emissions of carbon dioxide (mainly from burning fossil fuels in power stations and elsewhere) and of other more powerful but much less abundant ‘greenhouse’ gases including HFCs (hydrofluorocarbons). Under the auspices of the Montreal Protocol (Anon. 1987), the developed world ceased the production of ozone-depleting CFCs during the 1990s. This was made possible by the substitution of less environmentally harmful HCFCs. The HCFCs themselves are expected to be phased out by 2010–20, if not earlier, and in some applications there are no known effective substitutes at present available. In Europe, the use of CFCs in existing equipment will be banned, and the supply of new equipment using HCFCs will be prohibited. At the time of writing, dates for these limitations are still uncertain. These matters have two direct impacts on users of chilling equipment. Firstly, every change of technology costs money, and may in some cases result in an increase in running costs as well as re-equipment costs. Secondly, it may be necessary in the future to move from locally safe but globally harmful CFCs and HCFCs to globally safe but potentially locally hazardous substances such as ammonia and propane. These latter substances can be used safely, but there are added costs and added needs for proper training of equipment users. HFCs (hydrofluorocarbons) have been developed as alternatives. These do not deplete ozone and are widely available, but are being targeted by some environmentalists, as they are greenhouse gases within the Kyoto Protocol. The purchaser of equipment needs to be aware of these matters, as he may otherwise obtain machinery that will have to be modified or even replaced long before its expected economic life is over. There could also be financial implications at the time of machinery disposal. The reduction of CFC and HCFC use in insulating foams in storage cabinets and stores has been well publicised, but at the time of writing the implications for refrigeration machinery are insufficiently widely appreciated. A further related issue is the relation between global warming, energy use, and energy efficiency. New refrigerant fluids may be less efficient, but future environmental concerns may penalise excessive energy use. The equipment specifier is likely to face some difficult choices over the next few years. The user will face new responsibilities for minimising refrigerant leakage, ensuring efficient operation, and using only properly qualified maintenance staff. For a fuller discussion see (Heap 1998). 4.5 Chilled foods and refrigeration The benefit of chilled storage is the extension of life of the foodstuff in good condition, by slowing down the rate of deterioration. Chilling, it must be emphasised, cannot improve the quality of a poor product; neither can it stop the processes of spoilage – it can only slow them down (see Chapters 7, 9, 10). The refrigeration of chilled foods 83
84 Chilled foods For the international land transport of chilled (and frozen) foods, the UNECE Treaty Agreement on the International Carriage of Perishable Foodstuffs and on the Special Equipment to be used for such Carriage(ATP) lays down various provisions. Foods are classified and maximum temperatures are stated in the ATP agreement as follows(UNECE 1998) Red offal Butte Game +4°C Milk for immediate consumption +4°C Industrial milk Yoghurt kefir. cream. fresh cheese +4C Fish, molluscs, crustaceans in melting ice(0C) Unstabilized meat products +6°C Meat(not offal) +7°C Poultry, rabbits This list excludes prepared vegetable foods with or without dressings and fresh fruit and vegetables There are two quite distinct applications of refrigeration to chilled foods These are the chilling operation itself, in which the foodstuff is cooled from either an ambient temperature of maybe 30C or a cooking temperature of over 0oC, and the chilled storage, at a closely controlled temperature of between 1.5C and +150oC depending on the foodstuff Chilling equipment and chilled storage equipment are quite different in their requirements and their design, and although some chilling equipment may be used for chilled storage, storage equipment is not designed to cool products, only to maintain temperature Transport refrigeration for chilled food distribution is a special case of storage and transport equipment should not be expected to provide rapid cooling 4.6 Chilling The rate at which heat can be extracted during chilling is dependent on many factors. The size and shape of the pack or container will affect the rate of heat transfer to the cooling air (or, in some cases, water). The temperature and speed of the air will also affect this. Within the pack, the weight, density,water content, specific heat capacity, thermal conductivity, latent heat content, and initial food temperature will each play a part In the case of unpackaged foods, the factors leading to rapid cooling also lead to rapid loss of moisture, so it may seem that slow cooling is better. Generally his is not the case, as the extended cooling time is also an extended drying-out time. More rapid chilling is possible with thinner packs, with higher airspeeds, and with lower air temperatures. All these lead to higher operating costs, so equipment design has to be a compromise to give the best overall operating ystem. This means that available for different
For the international land transport of chilled (and frozen) foods, the UNECE Treaty Agreement on the International Carriage of Perishable Foodstuffs and on the Special Equipment to be used for such Carriage (ATP) lays down various provisions. Foods are classified and maximum temperatures are stated in the ATP agreement as follows (UNECE 1998): Red offal +3ºC Butter +6ºC Game +4ºC Milk for immediate consumption +4ºC Industrial milk +6ºC Yoghurt, kefir, cream, fresh cheese +4ºC Fish, molluscs, crustaceans in melting ice (0ºC) Unstabilized meat products +6ºC Meat (not offal) +7ºC Poultry, rabbits +4ºC This list excludes prepared vegetable foods with or without dressings and fresh fruit and vegetables. There are two quite distinct applications of refrigeration to chilled foods. These are the chilling operation itself, in which the foodstuff is cooled from either an ambient temperature of maybe 30ºC or a cooking temperature of over 70ºC, and the chilled storage, at a closely controlled temperature of between 1.5ºC and +15.0ºC depending on the foodstuff. Chilling equipment and chilled storage equipment are quite different in their requirements and their design, and although some chilling equipment may be used for chilled storage, storage equipment is not designed to cool products, only to maintain temperature. Transport refrigeration for chilled food distribution is a special case of storage, and transport equipment should not be expected to provide rapid cooling. 4.6 Chilling The rate at which heat can be extracted during chilling is dependent on many factors. The size and shape of the pack or container will affect the rate of heat transfer to the cooling air (or, in some cases, water). The temperature and speed of the air will also affect this. Within the pack, the weight, density, water content, specific heat capacity, thermal conductivity, latent heat content, and initial food temperature will each play a part. In the case of unpackaged foods, the factors leading to rapid cooling also lead to rapid loss of moisture, so it may seem that slow cooling is better. Generally, this is not the case, as the extended cooling time is also an extended drying-out time. More rapid chilling is possible with thinner packs, with higher airspeeds, and with lower air temperatures. All these lead to higher operating costs, so equipment design has to be a compromise to give the best overall operating system. This means that a range of equipment is available for different 84 Chilled foods