1、31.1CHAPTER 31POULTRY PRODUCTSProcessing 31.1Chilling 31.1Decontamination of Carcasses 31.4Further Processing 31.4Freezing 31.5Packaging . 31.7Airflow Systems in Poultry Processing Plants . 31.8Plant Sanitation 31.9Tenderness Control. 31.10Distribution and Retail Holding Refrigeration 31.10Preservin
2、g Quality in Storage and Marketing . 31.10Thawing 31.11OULTRY, and broilers in particular, are the most widely grownPfarm animal on earth. Two major challenges face the poultryindustry: (1) keeping food safe from human pathogens carried bypoultry in small numbers that could multiply, sometimes to da
3、nger-ous levels, during processing, handling, and meal preparation; and(2) developing environmentally sound, economical waste manage-ment facilities. Innovative engineering and refrigeration are a part ofthe solutions for these issues.PROCESSINGProcessing is composed of three major segments: Dressin
4、g, where the birds are placed on moving line, killed, anddefeathered.Eviscerating, where the viscera are removed, the carcass ischilled, and the birds are inspected and graded.Further processing, where the largest portion of the carcassesare cut up, deboned, and processed into various products. Thep
5、roducts are packaged and stored chilled or frozen.A schematic processing flowsheet is described in Figure 1;equipment layout for the dressing area is given in Figure 2 and forthe eviscerating area in Figure 3. The space needed in the productionarea for the various activities is shown in Figure 4. A
6、modern, highlyautomated poultry processing plant processes 1 to 3 million birdsper week. In the 1970s, a standard U.S. plant was processing 1500birds per hour (2 shifts, 5 days), or close to 120 000 birds per week.Barbut (2000) describes processing in detail.CHILLINGPoultry products in the United St
7、ates may be chilled to 3.5Cor frozen to lower than 3.5C. Means of refrigeration include ice,mechanically cooled water or air, dry ice (carbon dioxide sprays),and liquid nitrogen sprays. Continuous chilling and freezing sys-tems, with various means for conveying the product, are common.According to U
8、SDA regulations (1990), poultry carcasses with amass of less than 1.8 kg should be chilled to 4.5C or below in lessthan 4 h, carcasses of 1.8 to 3.6 kg in less than 6 h, and carcasses ofmore than 3.6 kg in less than 8 h. In air-chilling ready-to-cook poul-try, the carcasses internal temperature shou
9、ld reach 4.4C or lesswithin 16 hours (9CFR381.66).Slow air chilling was considered adequate for semiscalded, un-eviscerated poultry in the past. But with the transformation to evis-cerated, ready-to-cook, sometimes subscalded, poultry, air chillingwas replaced by chilling in tanks of slush ice. Imme
10、rsion chilling ismore rapid than air chilling, prevents dehydration, and effects a netabsorption of water of 4 to 12%. Per U.S. regulations (9CFR441.10),water retention in raw carcasses and parts must be shown to be anunavoidable consequence of processing, to the specifications of theFood Safety and
11、 Inspection Service (FSIS). Additionally, water-retaining poultry must carry a label stating the maximum percentageof water retained. Objections to this mass gain from external water,a concern that water chillers can be recontamination points, and thehigh cost of disposing of waste water in an envir
12、onmentally soundmanner have encouraged some operators to consider returning to airchillers.Continuous-immersion slush ice chillers, which are fed auto-matically from the end of the evisceration conveyer line, havereplaced slush ice tank chilling, a batch process. In general, tanksare only used to ho
13、ld iced, chilled carcasses before cutting up, or toage before freezing.The following types of continuous chillers are used:Continuous drag chillers. Suspended carcasses are pulledthrough troughs containing agitated cool water and ice slush.The preparation of this chapter is assigned to TC 10.9, Refr
14、igeration Appli-cation for Foods and Beverages.Fig. 1 Processing Sequence of Fresh PoultryFig. 1 Processing Sequence of Fresh Poultry31.2 2010 ASHRAE HandbookRefrigeration (SI)Slush ice chillers. Carcasses are pushed by a continuous series ofpower-driven rakes.Concurrent tumble systems. Free-floatin
15、g carcasses passthrough horizontally rotating drums suspended in tanks of, suc-cessively, cool water and ice slush. Movement of the carcasses isregulated by the flow rate of recirculated water in each tank.Counterflow tumble chillers. Carcasses are carried throughtanks of cool water and ice slush by
16、 horizontally rotating drumswith helical flights on the inner surface of the drumsRocker vat systems. Carcasses are conveyed by the recirculatingwater flow and agitated by an oscillating, longitudinally orientedpaddle. Carcasses are removed automatically from the tanks bycontinuous elevators.These c
17、hillers can reduce the internal temperature of broilersfrom 32 to 4.5C in 20 to 40 min, at processing speeds of 5000 to10 000 birds/h (Figure 5). Chillers must meet food safety require-ments (see, e.g., 9CFR381.66) and the facilitys Hazard Analysis ofCritical Control Points (HACCP) plan (see Chapter
18、 22).Adjuncts and replacements for continuous-immersion chillingshould be used, if available, because immersion chilling is believedto be a major cause of bacterial contamination. Water spray chilling,air blast chilling, carbon dioxide snow, or liquid nitrogen spray arealternatives, but with the fol
19、lowing limitations:Liquid water has a much higher heat transfer coefficient than anygas at the same temperature of cooling medium, so water immer-sion chilling is more rapid and efficient than gas chilling. Water spray chilling, without recirculation, requires much greateramounts of water than immer
20、sion chilling. Product appearance should be equivalent for water immersion orspray chilling, but inferior for air blast, carbon dioxide, or nitro-gen chilling, because of surface dehydration.Air chilling without packaging could cause a 1 to 2% loss of mois-ture, whereas water immersion chilling allo
21、ws from 4 to 15%moisture uptake, and water spray chilling up to 4% moistureuptake. Salt-brine chilling is the fastest chilling medium, but haslittle use in fresh poultry chilling.Coolant temperature and degree of contact between coolant andproduct are most important in transferring heat from the car
22、cass sur-face to the cooling water. The heat transfer coefficient between thecarcass and the water can be as high as 2000 W/(m2K). Mechanicalagitation, injection of air, or both can improve the heat transfer rate(Veerkamp 1995). Veerkamp and Hofmans (1974) expressed heatremoved from poultry carcasse
23、s by the following empirical relation-ship.(1)whereh = apparent heat transfer coefficient, W/(m2K)m = mass of the carcass, kg = cooling time, sQi= maximum heat removal, JFigure 5 shows time-temperature curves in a commercial counter-flow chiller and compares calculated and measured values.With adequ
24、ately washed carcasses and adequate chiller overflowin counterflow to the carcasses, the bacterial count on carcassesshould be reduced by continuous water-immersion chilling. How-ever, incidence of a particular low-level contaminant, such as Sal-monella, may increase during continuous water-immersio
25、n chilling;this can be controlled by chlorinating the chill water. However, forchlorine to be effective, the waters pH should be 7.0.Spray chilling without recirculation has reduced bacterial surfacecounts 85 to 90% (Peric et al. 1971). Microbe transfer by spray chill-ing is unlikely. Chilling with
26、air, carbon dioxide, or nitrogen presentsno obvious microbiological hazards, although good sanitary practicesFig. 2 Equipment Layout for Live Bird Receiving, Slaughtering, and Defeathering AreasFig. 2 Typical Equipment Layout for Live Bird Receiving, Slaughtering, and Defeathering AreasQQi- 0 . 0 0
27、9 h 0.73+loglog=0.194 h 0.187log m 0.564 h 2.219log+logPoultry Products 31.3are essential. If the surface of the carcass freezes as a part of the chill-ing process, the bacterial load may be reduced as much as 90%.Air or gas chilling is commonly used in Europe. In air-blastand evaporative chilling,
28、heat is conducted partly by the air-to-carcass contact and partly by evaporation of moisture from thecarcass surface. The amount of water removed by evaporationdepends on the carcass temperature, but even at 10C it is about1%. The apparent heat transfer coefficient ranges from 50 to200 W/(m2K). Majo
29、r disadvantages of air chilling are slowcooling, dripping from one bird to another in multitiered chill-ers, and mass loss during chilling. A diagram of a one-tieredevaporative air chiller is given in Figure 6. To reduce contamina-tion, it is very important that birds do not touch or drip on eachoth
30、er if multiple layers are used. Cryogenic gases are generally used in long insulated tunnelsthrough which the product is conveyed on an endless belt. Somefreezing of the outer layer (crust freezing) usually occurs, and thetemperature is allowed to equilibrate to the final, intended chilltemperature.
31、 Some plants use a combination of continuous waterimmersion chilling to reach 2 to 5C and a cryogenic gas tunnel toreach 2C. The water-chilled poultry, either whole or cut up, isgenerally packaged before gas chilling to prevent dehydration.Fig. 3 Equipment Layout for Eviscerating, Chilling, and Pack
32、aging AreasFig. 3 Typical Equipment Layout for Eviscerating, Chilling, and Packaging Areas31.4 2010 ASHRAE HandbookRefrigeration (SI)Ice requirements per bird for continuous immersion chillingdepend on entering carcass temperatures and mass, entering watertemperature, and exit water and carcass temp
33、erature. For a counter-flow system, 15C entering water and 18C exit water, 0.25 kg of iceper kilogram of carcass is a reasonable estimate. This may be com-pared to a requirement of 0.5 to 1 kg of ice per kilogram of poultryfor static ice slush chilling in tanks. For continuous counterflowwater-immer
34、sion chillers, if plant water temperature is considerablyabove 18C, it may be economical to use a heat exchanger betweenincoming plant water and exiting (overflow) chill water.Ice production for chilling is usually a complete in-plant opera-tion, with large piping and pumps to convey small crystalli
35、ne ice orice slush to the point of use. To reduce ice consumption, someimmersion chillers are double-walled and depend on circulatingrefrigerant to chill the water in the chiller. The chiller has an ammo-nia or refrigerant lubricant between the outer and inner jacket, withthe inner jacket serving as
36、 the heat transfer medium. Agitation or adefrost cycle must be provided during periods of slack production toprevent the chiller from freezing up.Chilling and holding to about 2C, the point of incipient freez-ing, gives the product a much longer shelf life compared with aproduct held at ice-pack tem
37、peratures (Stadelman 1970).DECONTAMINATION OF CARCASSESContamination of poultry meat by foodborne pathogens duringprocessing can be potentially dangerous if microbes multiply tocritical numbers and/or produce poisonous toxins (Zeidler 1996,1997). The Hazard Analysis of Critical Control Points (HACCP
38、)system (see Chapter 22 and the section on HACCP Systems inPoultry Processing) was specifically developed for each food toeliminate or keep pathogen levels very low so food-related illnessescannot break out. Appropriate refrigeration and strict temperaturecontrol throughout the food channel is vital
39、 to suppress microbialgrowth in high-moisture perishable foods and meats in particular.Decontamination steps are now being added just before chilling.Numerous methods have been developed (Bolder 1997; Mulder1995), including lactic acid (1%), hydrogen peroxide (0.5%), andtrisodium phosphate (TSP) spr
40、ays. Ozone (O3) is a strong oxi-dizer and can be used to decontaminate chiller and scalding water;however, it is very corrosive. Gamma irradiation of poultry is approved in many countries,including the United States; products are available for sale in a fewoutlets. The publics fear of this technique
41、 limits sales. However,the threat of food poisoning is reducing objections to irradiatedfoods because irradiation is very effective, and can kill 95.5% ofnon-spore-forming pathogens (Stone 1995). A dose of 2.5 kGy isthe most suitable for poultry.Steam under vacuum effectively kills 99% of the surfac
42、e bacte-ria on beef and pork carcasses and is used commercially. In this con-tinuous system, the carcass is carried on a rail to a chamber. Avacuum is pulled and steam at 143C is applied for 25 ms. Uponbreaking the vacuum, the carcass surface is cooled to prevent thesurface from cooking. USDA engine
43、ers developed steam equipmentfor poultry in 1996.FURTHER PROCESSINGMost chickens and turkeys, for both chilled and frozen distri-bution, are cut up in the processing plant. More than 90% of thebroilers in the United States are sold as cut-up products produced atFig. 4 Space-Relationship-Flow Diagram
44、 for Poultry Process-ing PlantFig. 4 Space-Relationship-Flow Diagram for Poultry Processing Plant(Square metres of floor space needed)Fig. 5 Broiler and Coolant Temperatures inCountercurrent Immersion ChillerFig. 5 Broiler and Coolant Temperatures in Countercurrent Immersion ChillerFig. 6 One-Tier E
45、vaporative Air ChillerFig. 6 One-Tier Evaporative Air ChillerPoultry Products 31.5the processing plant. The cutting procedure is almost fully auto-matic.Backs and necks are often mechanically deboned, giving a com-minuted slurry that is frozen in rectangular flat cartons containingabout 27 kg. Turke
46、y breasts, legs, and drumsticks are available asseparate film-packaged parts, and turkey thigh meat is marketed asa ground product resembling hamburger. Partial cooking and bread-ing and battering of broiler parts is done in poultry processingplants.Unit OperationsThe following types of equipment us
47、ed for further processing ofpoultry products are also used in red meat facilities.Size Reduction and Mixing Machines. Several types of size-reduction and mixing equipment are available.In grinding, meat is conveyed by an auger and forced through agrinding plate.Flaking is done by cutting blades lock
48、ed at a specific angle on arotating drum. Flaking does not extensively break muscle cells, asin grinding, and moisture loss and dripping are limited. Producttexture resembles muscle texture.Chopping is generally conducted with silent cutter equipment.Meat is placed in a rotating bowl with ice, which
49、 is used to keepthe temperature low, and vertical rotating blades chop the movingmeat. The length of chopping time determines the particle size.The end product is used in hot dogs and sausages.Mixing, tumbling, and injecting machines produce a uniformproduct out of various meats and nonmeat ingredients such as salt,sugar, dairy or egg proteins, spices, and flavorings. Together withsalt, mixing also helps extract myosin, which acts likes a glue inholding the product together. Injection machines insert an accurate and repeatable volume ofliquid
