1、33.1CHAPTER 33DAIRY PRODUCTSMilk Production and Processing. 33.1Butter Manufacture . 33.6Cheese Manufacture 33.10Frozen Dairy Desserts 33.13Ultrahigh-Temperature (UHT) Sterilization and Aseptic Packaging (AP) 33.19Evaporated, Sweetened Condensed, and Dry Milk. 33.22AW milk is either processed for be
2、verage milks, creams, andR related milk products for marketing, or is used for the manu-facture of dairy products. Milk is defined in the U.S. Code of Fed-eral Regulations and the Grade A Pasteurized Milk Ordinance(PMO). Milk products are defined in 21CFR131 to 135. Public Law519 defines butter. Not
3、e that there are many nonstandard dairy-based products that may be processed and manufactured by theequipment described in this chapter. Dairy plant operations includereceiving raw milk; purchase of equipment, supplies, and services;processing milk and milk products; manufacture of frozen dairydesse
4、rts, butter, cheeses, and cultured products; packaging; mainte-nance of equipment and other facilities; quality control; sales anddistribution; engineering; and research.Farm cooling tanks and most dairy processing equipment manu-factured in the United States meet the requirements of the 3-ASanitary
5、 Standards (IAMFES). These standards set forth the mini-mum design criteria acceptable for composition and surface finishesof materials in contact with the product; construction features suchas minimum inside radii; accessibility for inspection and manualcleaning; criteria for mechanical and chemica
6、l cleaning or sanitiz-ing in place (CIP and SIP); insulation of nonrefrigerated holdingand transport tanks; and other factors that may adversely affectproduct quality and safety or the ease of cleaning and sanitizingequipment. Also available is 3-A Accepted Practices, which dealswith construction, i
7、nstallation, operation, and testing of certain sys-tems rather than individual items of equipment.The 3-A Sanitary Standards and Accepted Practices are devel-oped by the 3-A Standards Committees, which are composed ofconferees representing state and local sanitarians, the U.S. PublicHealth Service,
8、dairy processors, and equipment manufacturers.Compliance with the 3-A Sanitary Standards is voluntary, butmanufacturers who comply and have authorization from the 3-ASymbol Council may affix to their equipment a plate bearing the3-A Symbol, which indicates to regulatory inspectors and purchas-ers th
9、at the equipment meets the pertinent sanitary standards.MILK PRODUCTION AND PROCESSINGHandling Milk at the DairyMost dairy farms have bulk tanks to receive, cool, and hold milk.Tank capacity ranges from 0.8 to 19 m3, with a few larger tanks. Ascows are mechanically milked, the milk flows through san
10、itary pipe-lines to an insulated stainless steel bulk tank. An electric-motor-driven mechanical agitator stirs the milk, and mechanical refrigera-tion begins to cool it even during milking.The Pasteurized Milk Ordinance (PMO) requires a tank to havesufficient refrigerated surface at the first milkin
11、g to cool to 10C orless within 4 h of the start of the first milking and to 7C or lesswithin 2 h after completion of milking. During subsequent milkings,there must be enough refrigerating capacity to prevent the tempera-ture of the blended milk from rising above 10C. The nameplatemust state the maxi
12、mum rate at which milk may be added and stillmeet the cooling requirements of the 3-A Sanitary Standards.Automatic controls maintain the desired temperature within apreset range in conjunction with agitation. Some dairies continu-ously record temperatures in the tank, a practice required by thePMO f
13、or bulk milk tanks manufactured after January 1, 2000. Be-cause milk is picked up from the farm tank daily or every other day,milk from the additional milkings generally flows into the reservoircooled from the previous one. Some large dairy farms may use aplate or tubular heat exchanger for rapid co
14、oling. Cooled milk maybe stored in an insulated silo tank (a vertical cylinder 3 m or more inheight).Milk in the farm tank is pumped into a stainless steel tank on atruck for delivery to the dairy plant or receiving station. The tanksare well insulated to alleviate the need for refrigeration during
15、trans-portation. Temperature rise when testing the tank full of watershould not be more than 1.1 K in 18 h, when the average temperaturedifference between the water and the atmosphere surrounding thetank is 16.7 K.The most common grades of raw milk are Grade A and Manu-facturing Grade. Grade A raw m
16、ilk is used for market milk andrelated products such as cream. Surplus Grade A milk is used for icecream or manufactured products. To produce Grade A milk, thedairy farmer must meet state and federal standards; a few municipalgovernments also have raw milk regulations.For raw milk produced under the
17、 provisions of the Grade A PMOrecommended by the U.S. Public Health Service, the dairy farmermust have healthy cows and adequate facilities (barn, milkhouse, andequipment), maintain satisfactory sanitation of these facilities, andhave milk with a bacteria count of less than 100 000 per mL for indi-v
18、idual producers. Commingled raw milk cannot have more than300 000 counts per mL. The milk should not contain pesticides, anti-biotics, sanitizers, and so forth. However, current methods detecteven minute traces of these prohibited substances, and total purity isdifficult. Current regulators require
19、no positive results on drug resi-due. Milk should be free of objectionable flavors and odors.Receiving and Storing MilkA milk processing plant receives, standardizes, processes, pack-ages, and merchandises milk products that are safe and nutritiousfor human consumption. Most dairy plants either rece
20、ive raw milkin bulk from a producer or arrange for pickup directly from dairyfarms. The milk level in a farm tank is measured with a dipstick ora direct-reading gage, and the volume is converted to mass. Fat testand mass are common measures used to base payment to the farmer.A few organizations and
21、the state of California include the percentof nonfat solids and protein content.Plants can determine the amount of milk received by (1) weigh-ing the tanker, (2) metering milk while pumping from the tanker toThe preparation of this chapter is assigned to TC 10.9, RefrigerationApplication for Foods a
22、nd Beverages.33.2 2010 ASHRAE HandbookRefrigeration (SI)a storage tank, or (3) using load cells on the storage tank or othermethods associated with the amount in the storage tank.Milk is generally received more rapidly than it is processed, soample storage capacity is needed. A holdover supply of ra
23、w milk atthe plant may be needed for start-up before arrival of the first tankersin the morning. Storage may also be required for nonprocessing daysand emergencies. Storage tanks vary in size from 4 to 230 m3. Thetanks have a stainless steel lining and are well insulated.The 3-A Sanitary Standards f
24、or silo-type storage tanks specifythat the insulating material should be of a nature and an amount suf-ficient to prevent freezing during winter in colder climates, or anaverage 18 h temperature change of no more than 1.6 K in the tankfilled with water when the average temperature differential betwe
25、enthe water and the surrounding air is 16.7 K. Inside tanks should havea minimum insulation R-value of 8, whereas partially or whollyoutside tanks have a minimum R-value of 12. R-value units are(m2K)/W. For horizontal storage tanks, the allowable temperaturechange under the same conditions is 1 K.Ag
26、itation is essential to maintain uniform milkfat distribution.Milk held in large tanks, such as the silo type, is continuously agi-tated with a slow-speed propeller driven by a gearhead electricmotor or with filtered compressed air. The tank may or may not haverefrigeration, depending on the tempera
27、ture of the milk flowing intoit and the maximum holding time.Refrigeration (if provided) of milk in a storage tank may use arefrigerated jacket around the interior lining of the silo or tank. Thiscooling surface may be an annular space from a plate welded to theoutside of the lining for direct refri
28、gerant cooling or circulation ofchilled water or a water/propylene glycol solution. Another systemprovides a distributing pipe at the top for chilled liquid to flow downthe lining and drain from the bottom. Some plants pass milk througha plate cooler (heat exchanger) to keep all milk directed into t
29、hestorage tanks at 4.4C or less. Direct refrigerant cooling must becarefully applied to prevent milk from freezing on the lining. Thislimits the evaporator temperature to approximately 4 to 2C.Separation and ClarificationBefore pasteurizing, milk and cream are standardized and blendedto control the
30、milkfat content within legal and practical limits. Nonfatsolids may also need to be adjusted for some products; some statesrequire added nonfat solids, especially for lowfat milk such as 2%(fat) milk. Table 1 shows the approximate legal milkfat and nonfatsolids requirements for milks and creams in t
31、he United States.One means of obtaining the desired fat standard is by separatinga portion of the milk. The required amount of cream or skim milk isreturned to the milk to control the final desired fat content. Milkwith excessive fat content may be processed through a standardizer-clarifier that rem
32、oves fat to a predetermined percentage (0.1 to2.0%) and clarifies it at the same time. To increase the nonfat solids,condensed skim milk or low-heat nonfat dry milk may be added.Milk separators are enclosed and fed with a pump. Separatorsdesigned to separate cold milk, usually not below 4.4C, have i
33、n-creased capacity and efficiency as milk temperature increases. Ca-pacity of a separator is doubled as milk temperature rises from 4.4to 32.2C. The efficiency of fat removal with a cold milk separatordecreases as temperature decreases below 4.4C. The maximumefficiency for fat removal is attained at
34、 approximately 7 to 10C orabove. Milk is usually separated at 20 to 33C, but not above 38Cin warm milk separators. If raw, warmed milk or cream is to beheld for more than 20 min before pasteurizing, it should be imme-diately recooled to 4.4C or below after separation.The pump supplying milk to the s
35、eparator should be adjusted tosupply milk at the desired rate without causing a partial churningaction.An automated process uses a meter-based system that controlsthe separation, fat and/or nonfat solids content, and ingredient addi-tion for a variety of common products. If the initial fat tests fed
36、 intothe computer are correct, the accuracy of the fat content of the stan-dardized product is 0.01%.At an early stage between receiving and before pasteurizing,the milk or resulting skim milk and cream should be filtered orclarified, optimally during the transfer from the pickup tanker intothe plan
37、t equipment. A clarifier removes extraneous matter andleucocytes, thus improving the appearance of homogenized milks.Pasteurization and HomogenizationThere are two systems of pasteurization: batch and continuous.The minimum feasible processing rate for continuous systems isabout 250 g/s. Therefore,
38、batch pasteurization is used for relativelysmall quantities of liquid milk products. The product is heated in astainless steel-lined vat to not less than 62.8C and held at that tem-perature or above for not less than 30 min. The Grade A PMOrequires that batch or vat pasteurizers keep the vapor space
39、 above liq-uid product at a temperature at least 2.8 K higher than the minimumrequired temperature of pasteurization during the holding period.Pasteurizing vats are heated with hot water or steam vapor in contactwith the outer surface of the lining. One heating method consists ofspraying heated wate
40、r around the top of the lining. It flows to the bot-tom, where it drains into a sump, is reheated by steam injection, andreturns to the spray distributor. Steam-regulating valves control thehot-water temperature. The maximum temperature differencebetween the milk or milk product throughout the vat d
41、uring its hold-ing period must not exceed 0.5 K. Therefore, the vat must have ade-quate agitation throughout the holding period. Whole and lowfatmilk, half-and-half, and coffee cream are cooled, usually in the vat, to54C and then homogenized. Cooling is continued in a heatexchanger (e.g., a plate or
42、 tubular unit) to 4.4C or lower and thenpackaged.Plate coolers may have two sections, one using plant water andthe second using chilled water or propylene glycol. The temperatureof the product leaving the cooler depends on the flow rates and tem-perature of the cooling medium.Most pasteurizing vats
43、are constructed and installed so that theplants cold water is used for initial product cooling after pasteuriza-tion. For final vat cooling, refrigerated water or propylene glycol isrecirculated through the jacket of the vat to attain a product temper-ature of 4.4C or less. Cooling time to 4.4C shou
44、ld be less than 1 h.High-temperature short-time (HTST) pasteurization is a contin-uous process in which milk is heated to at least 71.7C and held atthis temperature for at least 15 s. The complete pasteurizing systemusually consists of a series of heat exchanger plates contained in apress, a milk ba
45、lance tank, one or more milk pumps, a holding tube,Table 1 U.S. Requirements for Milkfat and Nonfat Solids in Milks and CreamsProductLegal MinimumMilkfat, % Nonfat Solids, %Federal RangeMost Often Federal RangeMost OftenWhole milk 3.25 3.0 to 3.8 3.25 8.25 8.0 to 8.7 8.25Lowfat milk 0.5 0.5 to 2.0 2
46、.0 8.25 8.25 to 10.0 8.25Skim milk 0.5* 0.1 to 0.5 0.5* 8.25 8.25 to 9.0 8.25Flavored milk 2.8 to 3.8 3.25 8.25 7.5 to 10.0 8.25Half-and-half 10.5 10.0 to 18.0* 10.5 Light (coffee) cream18.0 16.0 to 30.0* 18.0 Light whipping cream30.0 30.0 to 36.0* 30.0 Heavy cream 36.0 36.0 to 40.0 36.0 Sour cream
47、18.0 14.4 to 20.0 18.0 *MaximumDairy Products 33.3flow diversion valve, automatic controls, and sources of hot water orsteam and chilled water or propylene glycol for heating and coolingthe milk, respectively. Homogenizers are used in many HTST sys-tems as timing pumps used to process Grade A produc
48、ts. The heatexchanger plates are arranged so that milk to be heated or cooledflows between two plates, and the heat exchange medium flows inthe opposite direction between alternate pairs of plates.Ports in the plates are arranged to direct the flow where desired,and gaskets are arranged so that any
49、leakage will be from the prod-uct to the heating or cooling media, to minimize potential for prod-uct contamination. Terminal plates are inserted to divide the pressinto three sections (heating, regenerating, and cooling) and arrangedwith ports for inlet and outlet of milk, hot water, or steam for heat-ing, and chilled water or propylene glycol for cooling. To provide asufficient heat-exchange surface for the temperature change desiredin a section, milk flow is arranged for several passes through eachsection. The capacity of the pasteurizer
