ASHRAE REFRIGERATION IP CH 30-2010 MEAT PRODUCTS《肉制品》.pdf

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1、30.1CHAPTER 30MEAT PRODUCTSSanitation 30.1Carcass Chilling and Holding 30.2Processed Meats 30.12Frozen Meat Products. 30.16Shipping Docks 30.16Energy Conservation. 30.17ROUND the world about 4 to 5 million (0.4 million in theAUnited States) four-legged animals such as hogs, cattle, calves,buffalo, w

2、ater buffalo, lambs, sheep, goats, and deer are slaughteredeach day to supply the demand for red meats and their products.The majority of these animals are slaughtered in commercialslaughterhouses (abattoirs) under supervision, although a smallportion (0.08% in the United States) are still killed on

3、 the farm.The slaughter process from live animals to packaged meat prod-ucts is illustrated in Figure 1.SANITATIONSound sanitary practices should be applied at all stages of foodprocessing, not only to protect the public but to meet aestheticrequirements. In this respect, meat processing plants are

4、no differ-ent from other food plants. The same principles apply regardingsanitation of buildings and equipment; provision of sanitary watersupplies and wash facilities; disposal of waste materials; insect andpest control; and proper use of sanitizers, germicides, and fungi-cides. All U.S. meat plant

5、s operate under regulations set forth ininspection service orders. For detailed sanitation guidelines to befollowed in all plants producing meat under federal inspection,refer to the U.S. Department of Agricultures Agriculture Hand-book 570, the Food Safety and Inspection Service (FSIS), and Mar-rio

6、tt (1994).Proper safeguards and good manufacturing practices shouldminimize bacterial contamination and growth. This involves usingclean raw materials, clean water and air, sanitary handling through-out, good temperature control (particularly in coolers and freezers),and scrupulous between-shift cle

7、aning of all surfaces in contactwith the product.Precooked products present additional problems because con-ditions are favorable for bacterial growth after the product cools tobelow 130F. In addition, potential pathogen growth may be en-hanced because their competitor organisms were destroyed durin

8、gcooking. Any delay in processing at this stage allows surviving mi-croorganisms to multiply, especially when cooked and cooled meat ishandled and packed into containers before processing and freezing.Creamed products offer especially favorable conditions for bacterialgrowth. Filled packages should

9、be removed immediately and quicklychilled, which not only reduces the time for growth, but can also re-duce the number of bacteria.It is even more important during processing to avoid any oppor-tunity for growth of pathogenic bacteria that may have entered theproduct. Although these organisms do not

10、 grow as quickly at tem-peratures below 40F, they can survive freezing and prolonged fro-zen storage.Storage at about 25F allows growth of psychrophilic spoilagebacteria, but at 14F these, as well as all other bacteria, are dormant.Even though some cells of all bacteria types die during storage,acti

11、vity of the survivors is quickly renewed with rising temperature.The processor should recommend safe preparation practices to theconsumer. The best procedure is to provide instructions for cookingthe food without preliminary thawing. In the freezer, sanitation isconfined to keeping physical cleanlin

12、ess and order, preventingaccess of foreign odors, and maintaining the desired temperatures.Role of HACCPMany of the procedures for the control of microorganisms aremanaged by the Hazard Analysis and Critical Control Point(HACCP) system of food safety, which is described in Chapter22. It is a logical

13、 process of preventive measures that can controlfood safety problems. HACCP plans are required by the USDA inall plants. One aspect of the plan recommends that red meat car-casses and variety meats be chilled to 40F within 24 h, and thatthis temperature be maintained during storage, shipping, andpro

14、duct display.The preparation of this chapter is assigned to TC 10.9, Refrigeration Appli-cation for Foods and Beverages.Fig. 1 Steps of Meat ProcessingFig. 1 Steps of Meat Processing30.2 2010 ASHRAE HandbookRefrigerationCARCASS CHILLING AND HOLDINGA hot-carcass cooler removes live animal heat as rap

15、idly as pos-sible. Side effects such as cold shortening, which can reduce tender-ness, must be considered. Electrical stimulation can minimize coldshortening. Rapid temperature reduction is important in reducingthe growth rate of microorganisms that may exist on carcass sur-faces. Conditions of temp

16、erature, humidity, and air motion must beconsidered to attain desired meat temperatures within the time limitand to prevent excessive shrinkage, bone taint, sour rounds, surfaceslime, mold, or discoloration. The carcass must be delivered with abright, fresh appearance.Spray Chilling BeefSpraying col

17、d water intermittently on beef carcasses for 3 to 8 hduring chilling is currently the normal procedure in commercial beefslaughter plants (Johnson et al. 1988). Basically, this practice re-duces evaporative losses and speeds chilling. Regulations do not al-low the chilled carcass to exceed the prewa

18、shed hot-carcass weight.The carcass is chilled to a large extent by evaporative cooling. As thecarcass surface tissue dries, moisture migrates toward the surface,where it evaporates. Eventually, an equilibrium is reached when thetemperature differential narrows and reduces evaporative loss.When carc

19、asses were shrouded, once a common method forreducing weight loss (shrink), typical evaporative losses rangedfrom 0.75 to 2.0% for an overnight chill (Kastner 1981). Allen et al.(1987) found that spray-chilled beef sides lost 0.3% compared with1.5% for non-spray-chilled sides. Although variation in

20、carcassshrink of spray-chilled sides was influenced by carcass spacing,other factors, especially those affecting the dynamics of surface tis-sue moisture, may be involved. Carcass washing, length of spraycycle, and carcass fatness also affect shrinkage. With enough care,however, carcass cooler shrin

21、k can be nearly eliminated.Loin eye muscle color and shear force are not affected by spraychilling, but fat color can be lighter in spray-chilled compared tonon-spray-chilled sides. Over a 4 day period, color changes and driplosses in retail packs for rib steaks and round roasts were not relatedto s

22、pray chilling (Jones and Robertson 1989). Spray chilling couldprovide a moderate reduction in carcass shrinkage during coolingwithout having a detrimental influence on muscle quality.Vacuum-packaged inside rounds from spray-chilled sides hadsignificantly more purge (i.e., air removed) (0.9 lb or 0.2

23、6%) thanthose from conventionally chilled sides. Spacing treatments whereforeshanks were aligned in opposite directions and where they werealigned in the same direction but with 6 in. between sides both resultin less shrink during a 24 h spray-chill period than the treatmentwhere foreshanks were ali

24、gned in the same direction but with allsides tightly crowded together (Allen et al. 1987). Some studieswith beef (Hamby et al. 1987) and pork (Greer and Dilts 1988) indi-cated that bacterial populations of conventionally and spray-chilledcarcasses were not affected by chilling method (Dickson 1991).

25、However, Acuff (1991) and others showed that using a sanitizer(chlorine, 200 ppm, or organic acid, 1 to 3%) significantly reducescarcass bacterial counts.Chilling TimeAlthough certain basic principles are identical, beef and hog car-cass chilling differs substantially. The massive beef carcass is on

26、lypartially chilled (although shippable) at the end of the standardovernight period. The average hog carcass may be fully chilled (butnot ready for cutting) in 8 to 12 h; the balance of the period accom-plishes only temperature equalization.The beef carcass surface retains a large amount of wash wat

27、er,which provides much evaporative cooling in addition to that derivedfrom actual shrinkage, but evaporative cooling of the hog carcass,which retains little wash water, occurs only through actual shrink-age. A beef carcass, without skin and destined largely for sale asfresh cuts, must be chilled in

28、air temperatures high enough to avoidfreezing and damage to appearance. Although it must subsequentlybe well tempered for cutting and scheduled for in-plant processing,a hog carcass, including the skin, can tolerate a certain amount ofsurface freezing. Beef carcasses can be chilled with an overnight

29、shrinkage of 0.5%, whereas equally good practice on hog carcassesresults in 1.25 to 2% shrinkage.The bulk (16 to 20 h) of beef chilling is done overnight in high-humidity chilling rooms with a large refrigeration and air cir-culation capacity. The rest of the chilling and temperature equal-ization o

30、ccurs during a subsequent holding or storage period thataverages 1 day, but can extend to 2 or 3 days, usually in a separateholding room with a low refrigeration and air circulation capacity.Some packers load for shipment the day after slaughter, becausesome refrigerated transport vehicles have ampl

31、e capacity to removethe remaining internal heat in round or chuck beef during the firsttwo days in transit. This practice is most important in rapid deliveryof fresh meat to the marketplace. Carcass beef that is not shipped theday after slaughter should be kept in a beef-holding cooler at tem-peratu

32、res of 34 to 36F with minimum air circulation to avoid exces-sive color change and weight loss.Refrigeration Systems for CoolersRefrigeration systems commonly used in carcass chilling andholding rooms are operated with ammonia as the primary refriger-ant and are of three general types: dry coils, ch

33、illed brine spray, andsprayed coil.Dry-Coil Refrigeration. Dry-coil systems comprise most chill-ing and holding room installations. Dry-coil systems usually in-clude unit coolers equipped with coils, defrosting equipment, andfans for air/vapor circulation. Because the coils operate withoutcontinuous

34、 brine spray, eliminators are not required. Coils are usu-ally finned, with fins limited to 3 or 4 per inch or with variable finspacing to avoid icing difficulties. Units may be mounted on thefloor, overhead on the rail beams, or overhead on converted brinespray decks.Dry-coil systems operated at su

35、rface temperatures below 32Fbuild up a coating of frost or ice, which ultimately reduces airflowand cooling capacity. Coils must therefore be defrosted periodically,normally every 4 to 24 h for coils with 3 or 4 fins per inch, to main-tain capacity. The rate of build-up, and hence defrosting fre-que

36、ncy, decreases with large coil capacity and high evaporatingpressure.Defrosting may be done either manually or automatically by thefollowing methods:Hot-gas defrost introduces hot gas directly from the system com-pressors into the evaporator coils, with fans off. Evaporator suc-tion is throttled to

37、maintain a coil pressure of about 60 to 75 psig(at approximately 40 to 50F). The coils then act as condensersand supply heat for melting the ice coating. Other evaporators inthe system must supply the compressor load during this period.Hot-gas defrost is rapid, normally requiring 10 to 30 min for co

38、m-pletion. See Chapter 2 for further information about hot-gas de-frost piping and control.Coil spray defrost is accomplished (with fans turned off) byspraying the coil surfaces with water, which supplies heat to meltthe ice coating. Suction and feed lines are closed, with pressurerelief from the co

39、il to the suction line to minimize the refrigera-tion effect. Enough water at 50 to 75F must be used to avoidfreezing on the coils, and care must be taken to ensure that drainlines do not freeze. Sprayed water tends to produce some fog inthe refrigerated space. Coil spray defrost may be more rapid t

40、hanhot-gas defrost.Room air defrost (for rooms 35F or higher) is done with fansrunning while suction and feed lines are closed (with pressure re-lief from coil to suction line), to allow build-up of coil pressureMeat Products 30.3and melting the ice coating by transfer of heat out of the air flow-in

41、g across the coils. Refrigeration therefore continues duringdefrosting, but at a drastically reduced rate. Room air defrost isslow; the time required may vary from 30 min to several hours ifthe coils are undersized for dry-coil operation.Electric defrost uses electric heaters with fans either on or

42、off.During defrost, refrigerant flow is interrupted.Unit coolers may be defrosted by any one or combinations of thefirst three methods. All methods involve reduced chilling capacity,which varies with time loss and heat input. Hot-gas and coil spraydefrost interrupt chilling only for short periods, b

43、ut they introducesome heat into the space. Room air defrost severely reduces thechilling rate for long periods, but the heat required to vaporize ice isobtained entirely from the room air.Evaporator controls customarily used in carcass chilling andholding rooms include refrigerant feed controls, eva

44、porator pressurecontrols, and air circulation control.Refrigerant feed controls are designed to maintain, under vary-ing loads, as high a liquid level in the coil as can be carried withoutexcessive liquid spillover into the suction line. This is done by usingan expansion valve that throttles liquid

45、from supply pressure (typi-cally 150 psig) to evaporating pressure (usually 20 psig or higher).Throttling flashes some of the liquid to gas, which chills the remain-ing liquid to saturation temperature at the lower pressure. If it doesnot bypass the coil, flashed gas tends to reduce flooding of the

46、inte-rior coil surface, thus lowering coil efficiency.The valve used may be a hand-controlled expansion valve super-vised by operator judgment alone, a thermal expansion valve gov-erned by the degree of suction gas superheat, or a float valve (orsolenoid valve operated by a float switch) governed by

47、 the level offeed liquid in a surge drum placed in the coil suction line. This surgedrum suction trap allows ammonia flashed to gas during throttlingto flow directly to the suction line, bypassing the coil. The trap maybe small and placed just high enough so that its level governs that inthe coils b

48、y gravity transfer. Or, as in ammonia recirculation, it maybe placed below coil level so that the liquid is pumped mechanicallythrough the coils in much greater quantity than is required for evap-oration. In the latter case, the trap is large enough to carry its normaloperating level plus all the li

49、quid flowing through the coils, thuseffectively preventing liquid spillover to the compressors. Neverthe-less, it is necessary in all cases to provide further protection at thecompressors liquid return.Present practice strongly favors liquid ammonia recirculation,mainly because of the greater coil heat transfer rates with the resul-tant greater refrigerating capacity over other systems (see Chapter2). Some have coils mounted above the rail beams with 4 to 6 ft ofceiling head space. Air is forced through the coils, sometimes usingtwo-speed fans.Manual and thermal expansion valves