Frozen process of fish.pptx
- 1. PROCESSING OF MARINE PRODUCTS G BHARATHI ASSISTANT PROFESSOR DEPARTMENT OF FOOD AND DAIRY TECHNOLOGY
- 2. INTRODUCTION • The freezing process alone is not a method of preservation. It is merely the means of preparing the fish for storage at a suitably low temperature. In order to produce a good product, freezing must be accomplished quickly. A freezer requires to be specially designed for this purpose and thus freezing is a separate process from low temperature storage. • As with any type of food it is important to handle seafood safely to reduce the risk of foodborne illness, often called “food poisoning.” Follow these safe handling tips for buying, preparing, and storing fish and shellfish – and you and your family can safely enjoy the fine taste and good nutrition of seafood.
- 3. FREEZING OF STORAGE SEAFOOD • Only buy fish that is refrigerated or displayed on a thick bed of fresh ice (preferably in a case or under some type of cover). Because the color of a fish can be affected by several factors including diet, environment, treatment with a color fixative such as carbon monoxide or other packaging processes, color alone is not an indicator of freshness. The following tips can help you when making purchasing decisions: • Fish should smell fresh and mild, not fishy, sour, or ammonia-like. • A fish’s eyes should be clear and shiny.
- 4. •Whole fish should have firm flesh and red gills with no odor. Fresh fillets should have firm flesh and red blood lines, or red flesh if fresh tuna. The flesh should spring back when pressed •Fish fillets should display no discoloration, darkening, or drying around the edges. •Shrimp, scallop, and lobster flesh should be clear with a pearl-like color and little or no odor. •Some refrigerated seafood may have time/temperature indicators on their packaging, which show if the product has been stored at the proper temperature. Always check the indicators when they are present and only buy the seafood if the indicator shows that the product is safe to eat. •Fresh fish and fish fillets sold as “Previously Frozen” may not have all the characteristics of fresh fish (e.g., bright eyes, firm flesh, red gills, flesh, or bloodlines), however, they should still smell fresh and mild, not fishy, sour, or rancid.
- 5. GUIDELINES ON FREEZING • Look for the label: Look for tags on sacks or containers of live shellfish (in the shell) and labels on containers or packages of shucked shellfish. These tags and labels contain specific information about the product, including the processor’s certification number. • Discard Cracked/Broken Ones: Throw away clams, oysters, and mussels if their shells are cracked or broken.
- 6. • Do a “Tap Test”: Live clams, oysters, and mussels will close when the shell is tapped. If they don’t close when tapped, do not select them. • Check for Leg Movement: Live crabs and lobsters should show some leg movement. They spoil rapidly after death, so only live crabs and lobsters should be selected and prepared. Fish is largely water, normally 60-80 percent depending on the species, and the freezing process converts most of this water into ice. Freezing requires the removal of heat, and fish from which heat is removed falls in temperature in the manner shown in Figure 1. During the first stage of cooling, the temperature falls fairly rapidly to just below 0°C, the freezing point of water. As more heat requires to be extracted during the second stage, in order to turn the bulk of the water to ice, the temperature changes by a few degrees and this stage is known as the period of "thermal arrest". When about 55% of the water is turned to ice, the temperature again begins to fall rapidly and during this third stage most of the remaining water freezes. A comparatively small amount of heat has to be removed during this third stage.
- 7. FROZEN OF SEAFOOD • Frozen seafood can spoil if the fish thaws during transport and is left at warm temperatures for too long before cooking. • Don’t buy frozen seafood if its package is open, torn, or crushed on the edges. • Avoid packages with signs of frost or ice crystals, which may mean the fish has been stored a long time or thawed and refrozen. • Avoid packages where the “frozen” fish flesh is not hard. The fish should not be bendable.
- 8. Store Properly Put seafood on ice or in the refrigerator or freezer soon after buying it. If seafood will be used within 2 days after purchase, store it in a clean refrigerator at a temperature of 40°F or below. Use a refrigerator thermometer to check! Otherwise, wrap it tightly in plastic, foil, or moisture-proof paper and store it in the freezer. frozen storage of fish can give a storage life of more than one year, if properly carried out. It has enabled fishing vessels to rem ain at sea for long periods, and allowed the stockpiling of fish during periods of good fishing and high catching rates, as well as widened the market for fish products of high quality. The mechanism by which frozen fish deteriorates is somewhat different from that causing spoilage of chilled fish. Provided the temperature is low enough - below -10°C bacterial action will be stopped by the freezing process. Chemical, biochemical and physical processes leading to irreversible changes will still occur, but at a very slow rate. Deterioration during frozen storage is inevitable, and in order to obtain satisfactory results, fish for freezing must be of good quality.
- 9. The rate of oxidation can be reduced by reducing the exposure to oxygen. This can be achieved by introducing a barrier at the surface of the fish. Thus fish in a block keep better than fish frozen individually, and the addition of an ice glaze is beneficial. Glazing is carried out after freezing by brushing or spraying chilled water onto the surface of the fish or by dipping in cold water. Packaging materials, impermeable to moisture and oxygen can be effective, especially if vacuum packaging is employed. Some transfer of moisture from the product is unavoidable during freezing and frozen storage, which leads to dehydration of the fish. Good operating conditions are essential in order to keep dehydration to a minimum. It has been clearly established that fluctuating cold store temperatures are a major cause of dehydration. In practice the more severe cases of drying occur during frozen storage rather than during freezing. In extreme dehydration the frozen fish acquires a dry wrinkled look, tends to become pale or white in colour and the flesh become spongy. This characteristic appearance is called, inappropriately, 'freezerburn'.
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