Document ZBdm8mOJkKjao2ZN985NbgyN8

362 CHAPTER 32 1962 Guide And Data Boole procedure for removing surface bacteria has been indicated by Koona. Miller and Gorealme et al have reported a sub stantial decrease in bacterial contamination and an increase in shelf life by the use of low concentrations (10 to 20 ppm) of chlorine in the processing and chilling water. Kohler et al were able to increase shelf life of chilled poultry by the addition of 10 ppm of the antibiotic ehlortetracycline (aureomycin) to the water used to chill the eviscerated car casses. Both chlortetraq/dine and oxytetracydine have been proposed by producers of these antibiotics, and approved by Food and Dmg Administration as additives to poultry chill ing water. Many studies in laboratories and in commercial processing plants have been made in order to appraise the ttacfulneas and safety of this practice. Permissible amounts of chlortetraeycline in the chilled poultry carcass have been limited by federal regulations to seven parts per million, and it has been shown that much greater concentrations than this are completely destroyed during normal cooking. Experi mental results and conclusions on the amount of extended shelf life provided by the use of these antibiotics vary some what. However, different storage temperatures were used, initial bacterial loads probably varied between studies, and not all investigators determined the actual amounts of anti biotic introduced into the meat during the chilling or soaking period, Kohler et al found at least seven days additional shelf life at 37 F was provided to eviscerated poultry by chilling two hours in ice water containing 10 ppm of chlortetracycUne. Ziegler and Stadelman reported an extension of shelf life at' 36 F of about five days by a 10 min dip in solutions contain ing 10 to 40 ppm chlortetracycUne. Ayres el a! in tests on ten antibiotics, reported an extension of about 5 days shelf life at 40 F for chlortetracycUne, and comparable effectiveness for chlortetracycUne and oxytetiacycline at a concentration of 30 ppm. Control birds developed a bacterial population predominantly of the Pseudomonas, Achromcbocter type, while the chlortetracycUne treated samples developed significant proportions of yeasts. Yeasts were inhibited by two anti fungal antibiotics that had Utile effect on the other flora present; hence a combination of antibiotics was recom mended. In an evaluation of 15 min dips in water containing 10 ppm of chlortetracycUne, Shannon and Stadelman found that shelf life extension by antibiotic increased as the storage temperature was decreased, ranging from an additional day at 68 F to at least 10 days extension at 32 F. Baker reported as high bacterial counts in controls after eight days as chlor tetracycUne treated samples had after 19 days, at storage temperatures of 32 to 35 F. Vaughn et al obtained increases in storage life at 45 F of xero to three days by antibiotic treat ment in commercial type trials. Whole birds kept much better than those that had been cut up. In addition to aU of the preceding antibiotic tests, which refer to chickens, Kraft et al (1958) have demonstrated an extension of the shelf life of chilled turkeys by use of antibiotics. From the above results, it may be stated tentatively that antibiotics have a definite but Umited value in the handling of chilled poultry, and that they are certainly no substitute for good sanitation and low temperatures (near 32 F) in processing, transporation and retailing. Since shelf Ufe is limited to a considerable degree by bac terial growth (slime formation) on the skin layer, it is rea sonable to assume that drastic changes In the skin surface, such as the removal of the epidermal layer by high tempera ture scalding, might have an appreciable effect on shelf Ufe. Ziegler and Stadelman studied the effect of scalding tempera ture on shelf Ufe of chilled poultry and found that approxi mately one day more shelf life was obtained with 128 F scald than with 140 F scald. There is need for a rapid, reliable method for determining the numbers of bacteria on poultry, since most standard bacteriological counting techniques are tedious and time* .consuming. The resazurin dye reduction test, which corre lates well with bacterial contamination, has been suggested by Walker et al (1959) and by Wells (1959) as a possible rapid routine test in processing and distribution channels. PART : MILK PROCESSING The function of the milk plant is the blending, processing, packaging and distribution of fluid cows' milk and milk products for safe human consumption. Most dairy plants will receive milk from several dairy farms and, specializing in milk from one breed of dairy cattle, from various breeds of cattle. This milk is usually mixed, then processed by separa tion and blended to produce a milk which will contain a uni form quantity of butter fat as required for the various items being distributed. Pasteurization is an important step in toe processing as a means of destroying undesirable bacteria and for prolonging the keeping quality of the milk. Proper pas teurization will kill all pathogenic types of bacteria and nearly ail other objectionable organisms but other heat resistant types of bacteria will continue to multiply unless the milk is cooled promptly after the pasteurization process. The bacteria contained in milk will multiply quite rapidly if it is held for any length of time at temperatures above 50 F. For pro longed keeping time milk should be cooled as promptly as possible after being taken from the cow to a-temperature of 40 F or below and held at this temperature until it is con sumed. Although milk is one of our most perishable foods, with proper refrigeration and processing, it will retain its acceptable flavor for 15 days or longer after it has been taken from the cow. HANDLING MILK AT THE DAIRY FARM Milk is collected at the dairy farm in either milk cans or farm bulk milk tanks. If cans are used toe milk is usually cooled over a refrigerated Baudelot type cooler as toe milk is dumped from toe milker pails and before going into the cans. The night milking is usually held in a refrigerated room until the morning milking has been cooled and then both milkings &re transported to either a receiving station or direct to the milk plant. If a farm bulk tank is used the milk is dumped directly into toe tank from the milker pails or from the sanitary pipe of a milking system. The farm milk tank is insulated on sides and bottom and arranged with refrigerating surface built into the stainless steel lining of the tank. A motor driven agitator stirs the milk while it is being cooled. The motor is connected with the condensing unit so both will stop when the milk has reached the desired temperature as set on the thermostat. Smaller farm milk tanks may have the condensing unit built into one end to form a package unit but larger tanks are arranged for remote location of the condensing unit. The con. densing unit for the milk tank is sized so that all the milk from one milking will be cooled to 50 F within one hour after the milking has been completed. The second and other consecu tive milkings are' dumped directly into the tank with the milk already cooled. Milk from a bulk tank may be picked up at any time, day or night, depending on toe requirements of the milk plant and in some areas, or on smaller farms, may be picked up every other day. Milk from a bulk tank on the farm is picked up by an in sulated stainless steel milk tank truck and transported either directly to the milk plant or to a receiving station where it is transferred to a larger tank truck. Properly insulated milk tank trucks do not require refrigeration because the raise in Poultry and Dairy Products 363 Tabte 1 . Requirements for Percent Butterfat in Dairy Products Product _Skim mat ... Standard mils Special milk and half light cream (coffee) Heavy cream (whipping) Strfferfaf Not usually specified 3.0 to 3.8% 4.0 to 5.0% (as labeled) 10.0% (average) 16.0 to 20.0% 30.0 to 38-0% temperature of the milk in transporation will only be one or two degrees. If nflk cans are used in transporting milk from the dairy farin to a milk receiving station some refrigeration may be necessary at the station to precool the milk before it is re layed to the milk plant. The refrigerating equipment at the receiving station will be sized depending on the amount of cooling to be done and the size of the can washer being used. The milk will be cooled as fast as it can be received and is usually passed over a surface type cooler or a plate type heat exchanger and discharged directly into a tank truck for trans portation to the milk plant. If cans are used in transporting milk to the milk plant from the dairy farm it may be necessary to precool the milk at the plant unless closed trucks are used. Some dairy plants will receive milk both in cans and from tnk bucks. Many milk plants are now providing precooling equipment to oool incoming milk, from either cans or tank truck, to a temperature as low as 36 F before passing the milk to the bolding or storage tanks. This refrigerating load may fluctuate greatly and careful consideration should be given to the equipment selected. HOLDING TANKS Milk is usually received at the dairy plant faster, than it can be processed making it necessary to have insulated tanJrx to receive the milk and hold it until it can be pasteurized. Some plants operate only five days per week and require tank capacity for holding milk received for two days. Tanks are usually 2000 to 5000 gal in size but some specially built tacks are in use up to a 8000 gal capacity. These tanks have stain less steel linings insulated with two or three inch thick jacketed insulation and have some type of agitation to keep the butterfat uniformly mixed in the milk. If milk is received cold enough or if it is precooled before going to the tanks it may not be necessary to provide refrigeration for the milk in storage. If some cooling is desired in toe holding tanks they can be obtained with refrigerating surface built around the lining of the tank. This refrigerating surface may be an annular space formed by a plate welded to the outside of the lining suitable for direct expansion refrigeration or circulation of chilled water, or the surface may be arranged so chilled water will flow from a distributing pipe at the top and drain from toe bottom of the lining. The refrigerating surface built into a holding tank is usually designed for cooling the milk at a rate of one degree per hour but tanks having surface for a fester rate of cooling can be obtained. An evaporator tem perature of 28 F is the minimum that can be used for direct expansion cooling of milk to abqut 40 F without danger of freezing milk on the lining of the .tank. Milk will be continuously agitated while it is in a holding tank either by a slow speed propeller driven by a gear head motor or by filtered compressed air discharged into the tank by a perforated removable sanitary pipe extending along the bottom of the tank. Compressed air is visually supplied by a non-lnbricated type compressor at a pressure slightly higher than the static head of milk in toe tank. Without refrigeration, a tank holding 40 F milk in a 95 F room will warm up approximately three degrees in 24 hr when tank has 2-in. thick insulation and will warm up about two degrees with 3-in. insulation. STANDARDIZING Before going through toe pasteurizing process, the milk is standardized or Mended to produce a product containing the amount of butterfat desired for the item being processed. All states and most larger cities have laws which establish legal minimum standards, usually on a basis of percent butterfat content, and in many states toe percent of solids-not-fat is also specified. Table 1 shows toe range in percent butterfat as required for dairy products in various states. - The greater portion of milk being processed in a plant will be put out as standard milk which will require a lower percent butterfat than contained in the milk as received from the dairy farm. The standard desired is obtained by either sep arating a part of the milk to skim milk and cream, using the skim milk to reduce the overall butterfat content in tire milk or by removing the excess butterfat from toe milk as it is being passed to the pasteurizing process. Most milk separa tors now being used are the closed type requiring a pump to force the milk through the separator with the skim milk being discharged through one sanitary pipe to a skim milk tank and another pipe discharging cream to the cream vat. Hot milkseparators are available in capacities up to 20,000 lb of milk per hr and are designed for most efficient operation at milk temperatures of 90 to 100 F. Hot milk separation requires a means of heating the milk to the separating temperature. Equipment for cooling should be provided for both the cream and the kim milk as it leaves the separator before going to tanks or vats. Cold milk separators are used in many plants as a means of pJimjnating the heating and cooling processes required for the hot milk machines. Milk is separated at 40 F at a rate of 5500 lb per hr input for the largest machine. Pumps re quired to supply milk to the separator are operated at. a slower speed to prevent churning of the butterfat. The newest type separator used in milk plants is known as a standardizing clarifier. Tins machine will handle milk at temperatures of 40 F or higher and is designed to remove from 0.1 to 2.0 percent butterfat from the milk being passed through it. This unit can be arranged to take milk from the holding tanks, as it was received from the dairy farm at about 4.5 percent butterfat, and deliver milk to tire pas teurizing equipment at the standard desired for standard milk, for example, 3-5 percent. Thesurplus butterfat will be discharged as cream which can be used for blending to pro duce higher percent butterfat products. As a clarifier this unit separates out and holds in the bowl, sediment and ani mal tissue which otherwise should be removed from the milk by means of filters or strainers. In standardising the various items being distributed by a dairy plant there mil often be a surplus of skim milk or cream or both. To utilize this surplus many plants have added equipment to process buttermilk, cottage cheese, and butter. BATCH PASTEURIZATION Batch or holder type pasteurization is accomplished by filling a vat almost full with raw milk, holding it to a tempera ture of not less than 143 F and holding the milk at that tem perature or above for 9) minutes. After 30 minutes toe milk may be drawn from the vat and then cooled before it is passed