Document VjLwx1MyoJV1xZJ5zk1zQnqXK

440 CHAPTER 40 1962 Guide And Data Boofc Table 2 .... Average Water Content and Specific and latent Heats of Various Fishery Products R*b Water Content % Average freezing faint, f SpedAc Heat* Above freezing, tto/llb) (f deg) Spettfie Heafb Mow freezing, Bh//(ib)(f deg) Latent fteat* Bte/U ' Whole fish Haddock, Cod Halibut Tuna . Herrin* (kippered) Herrin* (smoked) Salmon Menhaden Rsh RBets or Sleaks Haddock, Cod, Ocean perch Hake, Whiting Pollock Mackerel Shell feh Scallop meat Shrimp American lobster Oysters and Clams (meat and liquor) 78 75 70 70 64 64 62 80 82 79 57 80 83 79 87 '6 0.82 28 0.80 28 0.76 28 0.76 0.41 28 0.71 0.39 28 0.71 28 0.70 0.38 28 0.84 28 0.86 28 0.83 28 0.66 0.37 28 0.84 28 0.86 0.45 28 0.83 28 0-90 0.46 112 108 100 100 92 92 115 118 113 115 119 113 125 C^lealAted by Sebd; 1'innuta; for nluM above freezing S - 0.008a + 0.20; for vahue below freezing S - 0.003 + 0.20 where a water content in mu,, 0^0 - areexfiefaentofaohdooDStitateBtoaf tbezufaetaace. " " Pew. M&VBtuT l0* beal llatem ht Iwaon) in Bin per lb. calcnlzted by multiplying the percentage*)? water content by the latent beat of fuaioa at water from the product and does not take into consideration the time required for freezing. The freezing time of a particular product varies with prod uct temperature, size and shape, method of packaging, re frigeration capacity, method of heat transfer between product and cooling medium (ia., blast, plate, shelf or immersion freezer) and temperature of the cooling medium. These factors are so closely interrelated that-it would be difficult to calcu late exactly how much any one factor will affect the freezing time. The freezing time can best be determined by experimen tation, recording the change in temperature of the particular sized product in question as it is being frozen in a plate, blast, shelf coil or immersion freezer (freezing times for various fishery products are^given in Table 1 and Figs. 1, 2, and 3). Once the freezing time of a particular product has been deter mined the refrigeration capacity in Btuh can be calculated by dividing the beat withdrawn from the product (Btu) by the time required for freezing (hr). Tons of refrigeration can then be calculated by dividing the heat In Btu per hr, removed from the product by 12,000 Btu. Assuming the product in Example 1 represents a 1-in. thick, 1 lb package of haddock fish fillets and it is found that the time required to lower the product temperature from 50 to 0 F is 1 hr if plate-frozen and 2 hr if blast-frozen the refrigeration capacity (q) required to remove the heat from 1 ton of product would be determined in the following manner. For plate-frozen fish fillets ,,,, 291,600 _ q - Q/h -------- j----- - 291,600 Btuh The refrigeration capacity necessary for product heat re moval must be increased by 25 to 50 percent in order to com pensate for heat leakage and other losses. The additional capacity, necessary would vary with the particular refrigera tion system. STORAGE OF FROZBJ HSH Fishery products may undergo undesirable changes is flavor, odor, appearance, and texture during frozen storage. These changes are attributable to dehydration (moisture loss ^ ,. 291,600 Tons of refrigeration ---------------- 24.3 12,000 For blast-frozen fish fillets 291,600 9 - Q/h -------- ----- - 145,800 Btuh Tons of refrigeration 145,800 - 12.2 12,000 Fig. 3 .... Freezing Packaged Fish Fillets and Slicks in Plate Freezer frpien fishery Products 441 the fish), oxidation of the oils or pigments and enzyme ^vity m the flesh. The rate at which these changes occur on (1) the composition of the particular species of TTTty the level and constancy of storage room temperature humidity; and (3) the protection afforded the product guougli the use of suitable packaging materials and glaring compounds- Effect of Composition on Quality The composition of-a particular species of fish affects its frozen storage life considerably. Fish having a high oil conteut, such as some species of salmon, tuna, mackerel and jgniog, have & comparatively short frozen storage life because 0f the development of rancidity due to the oxidation of the pfa lod pigments in the flesh. As often happens, there are (grtrin fish, as sablefish, that, despite high oil content, are quite resistant to oxidative deterioration in frozen storage. Table 3 . Relative Susceptibility of Representative Species of Fish to Oxidative Changes in Frozen Storage Severe Pink chub Moderate Flounders and sole Herring Mackerel Chum salmon Sheepshead Smelt Ocean perch Lake trout Tuna Minor Haddock Cod Oysters Halibut Lake herring Kbl<*trnh Coho salmon King salmon Red salmon Vert Slight Yellow pike Yellow perch Crab Lobster The development of rancidity may be of less importance in those fish having a low oil content. Therefore lean fish such as haddock and cod, if handled properly, can be kept in frozen storage for many months without serious loss of quality. The relative susceptibility of various species of fish to oxidative changes during frozen storage is shown in Table 3. Effect of Temperature on Quality Frozen fish must be kept at 0 F or lower in order to insure adequate shelf life. Storage above 0 F, even for a compara tively short period of time, will result in rapid loss of quality. Time-temperature tolerance studies recently initiated by the U. S. Bureau of Commercial fisheries show that frozen sea foods have memory; that is, each time they are subjected to high temperatures, or poor handling practices, the loss in quality is recorded. When the product is finally thawed, the total effect of each and all exposures to high temperatures or ether mistreatments is reflected in the quality of the product ri the consumer level Continuous and maintained storage *t temperatures lower than 0 F reduces oxidation, dehydra tion and enzyme changes resulting in longer product shelf life. It b important therefore that frozen seafoods be kept at tem peratures as close to 0 F as possible from the time frozen until reaching the consumer. Information of the shelf life of frozen fishery products *tored at different temperatures is given in Table 4. For many years it was thought too costly to operate rengerated warehouses lower than 0 F. However, in recent TB&ra improvements in the design and operation of refrigera te0 equipment have made operation of refrigerated ware- at --.10 F and --20 F economically possible. Many new ,rarEhouses are now being operated at --10 F or lower. Effect of Humidity on Quality A high relative humidity in the cold storage room will tend to reduce the evaporation of moisture from the product. The relative humidity of the air in the refrigerated room is directly affected by the temperature difference between the room cooling coils and the room, temperature. An increase in this temperature differential results in decreased relative humidity and accelerated rate of moisture withdrawal from the frozen product, likewise, small temperature differences between the air and the evaporator cooling coils results in a high relative humidity and reduced moisture loss from the product. The following example illustrates how the design of the re frigerated warehouse governs the relative humidity. Assume the cooling coil temperature is calculated to be --10 F and the room operating temperature 0 F. Then, during operation, moisture in the 0 F air (dry bulb temp) will be deposited on the cooling coils in the form of frost until a state of equilibrium is reached, and the dew point temperature of the 0 F air is the same as the coil temperature. Air at 0 F with a dew point tem perature of --10 F exerts a vapor pressure of 0.0108 psi. However, air completely saturated at 0 F has a dew point temperature of 0 F and exerts a vapor pressure of 0.0188. Therefore, the percent relative humidity for an empty room can be calculated by dividing the vapor pressure of the air at its dew point temperature (0.0108) by the vapor pressure of completely saturated air at its dry bulb temperature (0.0188). The relative humidity obtained would be 57.5 percent. The relative humidity in commercial freezers is 10-20 per cent higher than that of an empty freezer because of constant evaporation of moisture from the product. In a freezer oper ating at 0 F, with a 70 percent rh and pipe coil temp of --10 F, the moisture vapor pressure of the air within the package and in direct contact with the frozen fish would be 0.0188. The air in the freezer would, however, have a vapor pressure of 0.0132 and tiie moisture vapor pressure at the coils would be 0.0108. These differences in moisture vapor pressure will result in considerable moisture loss from the product unless it is ade quately protected by suitable packaging materials or glazing Table 4 .... Review of Effect of Storage Temperature on Shelf life of Some Frozen Fishery Products frodoct Packaged Haddock FQlets Tanw pMn. bn, f 10 0 -20 Packaged CodFulets Packaged Pollock fillets 10 0 -10 10 0 -20 Packaged Ocean Perch Fillets 15 10 0 -10 Packaged Striped Bass Fillets 15 0 SMf life. MonO. Product 4 to 5 11 to 12 Longer thAtx 12 Glazed Whole Halibut Tecs- tun, F 10 0 -10 -20 Shelf life. Moods* 3 6 9 12 5 Whole 10 6 Bhie Fin 0 to --5 10 to 11 Tuna -20 4 8 12 into 2 'Glazed 10 Whole Herring Longer tti*n )2 0 -17 6 9 1J4 to 2 Packaged 3Mto4 Mackerel 6 to 8 fillets 9 to 10 15 0 -10 2 3 3 to 5 fi4 Glazed 14 9 Blocks of Whale --4 Meat 3 6 12