Document nNrmODMEo66qV0zgQGp1mwax2

438 CHAPTER 40 TIME (HOURS) TO FREEZE FISH TO 20 F Fig. 2 .... Freezing Time for Tuna immersed in Brine of direct immersion-freesing machines were developed for freezing whole or panned fish These machines were generally unsuitable for freezing packaged fishery products, which make, up the bulk of frozen fish production, and have been replaced by methods employing air cooling, contact with refrigerated plates or shelves, or combinations of these meth ods. Immersion freezing is limited mostly to the freezing of tuna, shrimp, salmon, and halibut at sea and to the freezing of shrimp ashore. Extensive research has been conducted on brine-freezing groundfisb aboard the vessel, but this method is not yet in commercial use. An important consideration in immersion freezing of fish is tire selection of a suitable freezing medium. The requirements of such a freezing medium are that it be: non-toxic, acceptable to public health regulatory agencies, easy to renew, inexpen sive and have a low freezing temperature and viscosity. It is difficult to obtain a freezing medium that meets all of these requirements. For many years sodium chloride brine was the only freezing medium employed commercially in freezing fi*HHowever, experiments by the Bureau of Commercial Fisheries yielded another acceptable freezing medium containing a mix ture of glucose and salt in water. This medium reduces salt penetration into the fish and at the same time provides a pro tective glaze. More recently glycol and glycerine solutions have been used as freezing mediums. However, they have not as yet been used commercially for freezing fishery products because of their high cost. Immersion freezing of shrimp. A very snail quantity of the shrimp landed in the United States are immersion frozen both on the vessel and ashore. A glucose (20%)-saJt (20%) solution is employed because it permits the shrimp to freeze individually without fusing together, and also minimizes salt penetration. Commercial equipment is available for freezing shrimp aboard the fishing vessel One system in general use employs a stainless steel tank located on the deck of the vessel. Refriger ant 12 circulating through evaporator coils located in one section of the tank provides the necessary refrigeration effect, maintaining the glucose-salt brine at temperatures of 0 to 1962 Guide And Data Bo^ ' --5 F. A hydraulically driven propeller inside the tank f nishes the necessary brine circulation. Shrimp, when i4njUr* on the vessel, are headed and washed, weighed in 50 or?- lb lots and sorted into wire mesh freezer baskets. Thl! baskets are then immersed in the brine within the freel tank. After the proper freezing time elapses, about 15 minut^ the baskets are picked up and the shrimp put into 5Q 25^ or smaller sized cartons and stored in the refrigerated hoy Jr the vessel. There are several shore-side immersion systems t freezing fresh, iced shrimp, unloaded from the fishing vesuri One system is similar to that just described for use on u vessel. The freezing tanks may be somewhat larger but esseo- tially the shrimp are frozen in the same manner. Anotl*r type of immersion freezing system in use provides continuous freezing. This freezer employs a conveyor belt, located over* steel tank and serviced by a series of nozzles. The equipment is located within a heavily insulated enclosure. The shrimp to be frozen are placed on the conveyor belt. A glucose-salt brine pumped from the steel tank reservoir through a heat ts- changer where it is cooled to 0 F, is discharged from the spray nozzles located over the conveyor belt and flows over the shrimp, thereby freezing them. Immersion freezing of tuna. The majority of the tuna har vested in this country are brine-frozen aboard the fishing vessel. Freezing at sea enables the fishing vessel to mat* fa extended voyages necessary, because of the poor availability of tuna, and return to port with a full payload of high-quality fish. Tuna are frozen in brine wells which are lined with galva nized pipe coilson the inside. Direct expansion of ammonia info the evaporator coils provides the necessary refrigeration effect. The wells are so designed that the tuna can first be precooled and washed with refrigerated sea water, and then frozen in an added sodium chloride, brine. After the fish are frozen, the brine is pumped overboard and the tuna kept in 10 F dry stor age. Prior to unloading, the fish are thawed in a 33 F brine00 the vessel. In some cases the fish are thawed in tanks at the cannery. Therefore, if the fish are thawed ashore, thawing on the vessel is not required beyond the stage needed to separate thosefused together in the vessel's wells. In freezing tuna, sometimes the fish are held in the weiis for a long period of time prior to freezing, or frozen at a very slow rate because of high well temperatures caused by overloading, insufficient refrigeration capacity or inadequate brine circa- tion. Any of these practices will have 8 detrimental effect on the quality of the product, especially the smaller fish which are more subject to salt penetration and quality changes. Tuns not promptly and properly frozen may absorb excessive quantities of salt, rendering them of inferior quality, and may even be bacteriologically spoiled when landed. Studies by the Bureau of Commercial Fisheries show that tuna may require 5-72 hr to freeze, depending on the size of the fish and the freezing procedures used. Some freezing tunes for tuna of various sizes are shown in Fig. 2. Immersion freezing of groundfish. An immersion freezing system for freezing New England groundfish was developed by the Bureau of Commercial fisheries and installed on its vessel Delaware. Results of this research show that freezing groundfish at sea will enable the vessel to stay out until a full pay load is obtained and return to port with top quality fch- In developing equipment and handling procedures for freezing fish at sea many technical problems were solved, resulting the development of freezing and thawing techniques which will make posable the landing of frozen fish, which can be kept in cold storage and thawed, filleted and the fillets *** frozen and marketed as uniformly high quality fish. Id immersion freezing groundfish aboard the vessel Dd* ?B^"'fishery Prodoch 439 . ^ Freezing Time for Whole Round Cod and f*" Hoddock, of Various Thicknesses, in Sodium Chloride Brine tare, z 23 percent sodium chloride brine was used as a freezing ^inm. Tbe freezer consisted of a steel tank extending from zbove the deck to the bottom of the fish hold. The fish were with sea water, then put in the round into cylindrical pfranised metal mesh baskets located within the tank and connected' at each end by a continuous chain drive. Move ment of the baskets through the 0 F brine enabled constant renewal of the film of brine surrounding the fish, insuring rapid freering. A ratio of about 20-25 lb of fish per cu ft of basket space vss used to prevent packing of this fish. When the proper freezing time elapsed (Table 1) the fish were removed from the individual freezing baskets (which are numbered), glazed with sea water,and put into the 0 F refrigerated hold. For iMiimnm protection the frozen fish were glazed with fresh water during unloading, then transferred to wooden boxes for holding during frozen storage. For processing, the fish were moved from frozen storage and thawed by flooding the box, or a suitable thawing tank if used, with fresh potable water or clean sea water for three to four hours. The fish were then filleted by mashing or hand, *nd the fillets are frozen and marketed. Tests conducted show that fillets from fish frozen at sea compare favorably with fish kept no more than a few days on ice. Fish of this latter level of quality are seldom available 00 a commercial scale. Salt penetration studies showed that, as the brine tempera ture and the period of immersion increased, the salt penetra tion into the fish also increased. However, use of proper freez ing procedures resulted in negligible increase in salt content of the fish. In investigations on thawing it was found that rapid thaw ing in water removed most of the salt that penetrated into the fish during freezing and resulted in a firm, fresh fillet. Air thawing did not produce as satisfactory results from the standprint of residual salt content and quality of thawed fish. In zdditwo, glaring studies have shown that increased storage file can be obtained by washing the brine off the fish with sea *rier after they are frozen and reglaring the fish with fresh water during unloading from the vessel. Freezing of salmon at sea was adapted on a commercial ksia after World War H, so that the vessels could make longer tops and still land high quality fish. However, the success of refrigerated sea water in preserving fish in recent years has resulted in conversion of some freezer boats and construction f new vessels for storing fish in refrigerated sea water. The *pnpment, labor, and handling costs associated with the use ^refrigerated sea water are much less than those for freezing at sea. Therefore, storage in refrigerated aea water might eventually replace freezing at sea, for species of fish such as "hWt and salmon. These same techniques of holding fish in ^frigerated brine have been tried to provide hold-over facili- ties at the preceding plant and show considerable promise in reducing plant operating costs without loss in quality of the raw material prior to processing. Immersion freezing of salmon, and other species offish. Some salmon are still brine-frozen in tanks or wells located in the vessel The refrigeration effect is provided by ammonia or other suitable refrigerant flowing through pipe coils lining the insides of the tanks. A propeller type agitator or a brine pump provides the necessary brine circulation. A typical freezing operation is a 22 percent sodium chloride brine, made up in the freezer t"-nk and then chilled to about 5 F. Round salmon are then brailed into the tank and allowed to freeze. After the fiaVi are frozen (about eight hours is required for freezing) the brine is pumped to another t-nk for use in freezing additional quantities of fish The frozen salmon may then be kept in the dry refrigerated tank for a few hours, providing sufficient re frigeration capacity is available. Transfer of the fish from the freezing tank to the 0 F refrigerated hold is then accomplished by removing a cover plate at the bottom of the tank and allowing tbe fish to flow from tbe tank, through an opening in the deck into the refrigerated hold. CALCULATION OF REFRIGERATION REQUIREMENTS The total refrigeration requirements for freezing fish or other food products can be determined by calculating the product load and the refrigerator heat load. The latter is due to h**t gain through the insulated structure, air infiltration due to personnel usage, dissipation of electrical energy in the refrigerator space (lights, fans, motors, etc.) and losses due to equipment operating efficiency. The calculation of refrigerator heat load is discussed in Chapter 27 of the 1961 Guide And Data Book and would not vary appreciably between freezers for fish and other food products. Therefore, this section is concerned with only tbe refrigeration requirements that are necessary to remove the heat from fishery products and ac complish the necessary cooling and freezing. The heat load required to freeze a product is: q - WICIU -U) +hf + CAW - *.)] (1) where * Q -- heat removed, Btu. W ~ weight of product, pounds. c ~ specific heat above freezing, Btu per (pound) (Fahrenheit degree). d = specific heat below freezing, Btu per (pound) (Fahrenheit degree). kf = latent heat of fusion, Btu per pound. (1 * initial temperature of product, Fahrenheit. W " temperature at which the latent heat is removed from the product, Fahrenheit. (a a final temperature of frozen product, Fahrenheit. Example 1 illustrates the use of Equation 1. Specific heat, lateot beat and freezing point of various fishery products are given in Table 2. Example 1: Determine heat, expressed in Btu, that must be removed to lower the temperature of 2000 lb of haddock fish fillets from 5Q-0 F. Solution: Q - tF|C(W0 + hif + CAW - i)l Q = 2000 (0.84(50 - 28) + 115 + 0.44(28 - 0)1 Q - 291,600 Btu. Thus to freeze 1 ton of fish from 50-0 F, 291,600 Btu are required. However, Equation 1 merely shows the Btu removed