Fish Preservation MBT, lecture 7 Tahir
Why and how does freshly caught fish spoil? • Freshly caught fish spoil easily and need to be properly preserved. The five most popular methods of fish preservation are freezing, canning, smoking, and pickling and drying. • Top quality fresh fish are essential for fish preservation. Of all flesh foods, fish is the most susceptible to tissue decomposition, development of acidity, and microbial spoilage. • Spoilage and slime-producing bacteria are present on every fish and multiply rapidly on a dead fish held in warm surface water. • Fish begin to deteriorate as soon as they leave the water. To delay spoilage, clean the fish as soon as possible. • Thorough cleaning of the body cavity and chilling of the fish will prevent spoilage. Fish spoilage occurs rapidly at summer temperatures; spoilage is slowed down as freezing temperatures are approached.
Drying Fish • Several preservation methods are followed over the world for preserving fish. Aim of all these methods is same- to extend the shelf-life of fish so that the fish can be used in future properly. • One of these methods is “drying” which is the oldest known method of preserving perishable food items including fish • In Bangladesh, sun drying is the most widely used method of fish preservation. This method is also considered as the least expensive method of preservation.
Drying Fish • Drying involves removal of water content from the fish body. • Generally two terms are now being commonly used in drying of fish viz. “sun drying” and “dehydration” • These two methods of preserving fish are almost similar but with little differences. • In Sun drying this process is carried out by exposing target fish directly under the sun. This is usually done in the open air using solar energy to evaporate the water content in the fish. • Natural air carried away the evaporated water from fish body.
Dehydration • Dehydration, almost same as sun drying, except that this process is practiced under controlled operational parameters like air temperature, relative humidity, air velocity etc. • Common practice is to dry fish in an enclosure provided with facilities to control these parameters. Japanese equipment technology and Japan scale type hot blast technique are more commonly used. • Low temperature dehydration and drying room • The international advanced low temperature dehydration drying machine , mainly for the processing of dried sea cucumber and other can be aquatic products processing such as: holothurian, abalone, carp, seasoned squid , fish, dried shrimp
Advantages of dried fish: • Dried fish processed through sun drying or dehydration is highly concentrated fish compared to other preserved form of fish. • As water content become reduced so microbial activity can not run at normal rate thus reduce the spoilage of fish. • Less expensive method and comparatively simple procedure. • Under Reduced water content, enzymatic and many chemical process which are responsible for fish spoilage retarded. • In this method, complicated machinery and equipment are not required. • Dried fish remain stable at most ambient temperature.
Disadvantages of sun drying: • The major problem of sun drying is efficiency and quality of final product remain at the mercy of nature (i.e. operational parameters). • In improper sun drying, dried product suffers from many disadvantages. Some of these problems are- • This process is can only be carried out when bright sunlight is available. Also no control over the operational parameters. • Long duration required. Sometimes under unfavorable operational parameters it takes several days to complete which affects the quality of final product. • In sun drying, possibility of contamination with dust, sand; infestation with insects, their eggs and larvae is high. • Shelf life of the final product is not too long and poor quality final product is produced in most cases.
Driers • Driers are devices used to dry fish under controlled environment. • A variety of driers are used for drying fish, e.g. Cabinet drier, Kiln drier, Tunnel drier, Spray drier, Solar tent drier etc. • Preservation is essential for extra catches. Considering the economic and other conditions of dry fish farmers and existing facilities and weather of the country Bangladesh, sun drying of fish is considered best way to preserve fish. • But dry fish farmers need financial support and training on basic knowledge of scientific drying process.
Freezing fish • This is the simplest, most convenient, and most highly recommended method of fish preservation. A good quality frozen product requires the following: • Careful handling of the fish after catching. • Wrapping material or method that is airtight and prevents freezer burn and the development of undesirable flavors. • A freezer storage temperature of 0° F or lower. To freeze fish • Option 1 • Remove the guts and thoroughly clean the fish soon after catching. • Prepare the fish as you would for table use. Cut large fish into steaks or fillets. Freeze small fish whole. • Wrap the fish in heavy-duty freezer bags. Separate layers of fish with two thicknesses of packaging material for easier thawing. • Store at 0° F or lower. When ready to use, thaw in the refrigerator. • Option 2 • Cut large fish into steaks or fillets. Small fish, such as sunfish and panfish, or small servings of fish can be frozen in ice. • Place the fish in a shallow pan or water-tight container. Cover with ice water and place in the freezer until frozen (8-12 hours). Remove block from container, wrap, and store in freezer.
the storage life of good quality frozen fish held at 0° f or lower follows: • Northern pike, trout, whitefish, smelt, lake herring, carp – four to six months • Chinook salmon, coho salmon, white bass – five to eight months • Walleye, bass, crappie, sunfish, yellow perch, blue gill – eight to twelve months (Source: Minnesota Sea Grant, 2012)
Canning fish • Fish is a low acid food and can be processed safely only at temperatures reached in a pressure canner. Failure to heat process fish at 240° F or higher may allow spores of the dangerous heat-resistant bacteria, Clostridium botulinum, to survive, germinate, and grow. • The poison produced by botulinum bacteria causes botulism, a deadly food poisoning. The addition of small amounts of vinegar, or packing fish in tomato juice or tomato paste, does not remove the requirement for heat processing fish in a pressure canner. • Use standard heat-tempered canning jars. . Wide-mouth pint jars will be easier to fill than narrower ones. • General USDA method for canning fish without sauce (including blue, mackerel, salmon, steelhead, trout, and other fatty fish except tuna)
Canning fish • Note: Glass-like crystals of magnesium ammonium phosphate sometimes form in canned salmon. There is no way for the home canner to prevent these crystals from forming, but they usually dissolve when heated and are safe to eat. • PROCEDURE • Clean and gut fish within 2 hours after catching. Keep cleaned fish on ice until ready to can. • Remove head, tail, fins and scales. Wash and remove all blood. • Split fish lengthwise, if desired. Cut cleaned fish into 3½ inch lengths. • Fill pint jars, skin side next to glass, leaving 1 inch headspace. Do not add liquids. Adjust lids and process. • Pints—100 minutes 11 PSI • Weighted-gauge Pressure CannerPints—100 minutes 15 PSI • Heat fish to boiling temperatures for 10 minutes before tasting or serving. Canning fish in quart jars • http://www.uaf.edu/ces/pubs/catalog/detail/index.xml?id=
Pickling • Pickling is an easy method of preserving fish. • Pickled fish must be stored in the refrigerator at no higher than 40° F (refrigerator temperature), and for best flavor must be used within four to six weeks. • Only a few species of fish are preserved commercially by pickling, but almost any type of fish may be pickled at home. • Refrigerate the fish during all stages of the pickling process. • Ingredients for Pickled Fish • Fish – Use only fresh, high quality fish. • Water – Avoid hard water, as it causes off color and flavors. • Vinegar – Use distilled, white vinegar with an acetic acid content of at least 5 percent This percentage of acetic acid is needed to stop bacterial growth. • Salt – Use high grade, pure canning or pickling salt. It does not contain calcium or magnesium compounds which may cause off color and flavors in pickled fish. • Spices
General method for precooked pickled fish • Soak fish in a weak brine (1 cup salt to 1 gallon of water) for one hour. • Drain the fish; pack in heavy glass, crock, enamel, or plastic container in strong brine (2-½ cups salt to 1 gallon of water) for 12 hours in refrigerator. • Rinse the fish in cold water. • Combine the following ingredients in a large pan or kettle. This makes enough for 10 pounds of fish. • ¼ oz bay leaves • 2 T allspice • 2 T mustard seed • 1 T whole cloves • 1 T pepper, ground • 1-2 T hot, ground dried pepper • ½ lb onions, sliced • 2 qt distilled vinegar • 5 c water (avoid hard water of high mineral content) • Bring to a boil, add fish, and simmer for 10 minutes until fish is easily pierced with a fork.
General method for precooked pickled fish • Remove fish from liquid, place on a single layer on a flat pan. Refrigerate and cool quickly to prevent spoilage. • Pack cold fish in clean glass jars, adding a few whole spices, a bay leaf, freshly sliced onions, and a slice of lemon. • Strain the vinegar solution, bring to a boil, and pour into jars until fish is covered. • Seal the jar immediately with two-part sealing lid, following the manufacturer's instructions. • Pickled fish must be stored in the refrigerator as stated in general directions.
Caution: the broad fish tapeworm • The broad fish tapeworm infection can be contracted by humans from eating raw or undercooked species of fish found in the Great Lakes area. • Those who wish to prepare raw pickled fish should first freeze the fish at 0° F for 48 hours. • The larvae of the broad fish tapeworm pass through smaller fish until they lodge as hatched small worms in the flesh of large carnivorous species of fish, like northern pike, walleye pike, sand pike, burbot, and yellow perch. This worm, if eaten by humans in its infective stage, can attach to the small intestine and grow to lengths of 10 to 30 feet. • The infective worms are destroyed readily either by cooking or freezing. Two recent outbreaks of this tapeworm in Minnesota were related to eating uncooked pickled pike. • Those who wish to prepare raw pickled fish should first freeze the fish at 0° F for 48 hours.
Smoking fish • Smoking has long been used as a means of temporarily preserving fish. • The steps in the smoking process are necessary not only for safe preservation, but also to produce good flavor and aroma. • Carp, suckers, buffalo catfish, salmon, trout, and chubs may be successfully smoked. • A safe, high quality product can be produced using the following brining and smoking procedures. • Certain steps in the brining and smoking process require careful attention. • Brining • Use correct amount of salt in the brine. • Use enough brine for a given amount of fish. • The temperature during brining must be no higher than 40° F. • Use similar size and kinds of fish in the brine. • Smoking • There should be uniform heat treatment of all fish in the smoking chamber. • Use freshly caught, dressed fish, whole or filleted. Wash fish thoroughly.
Steps for safe smoked fish • Use freshly caught, dressed fish, whole or filleted. Wash fish thoroughly. • Fish for smoking must be brined. • 1 ½ cups salt to 1 gallon water—12 hours in refrigerator. • 4 cups salt to 1 gallon cold water—15 minutes. • Remove from brine, rinse. • Place short stem of meat thermometer in thickest portion of flesh of largest fish. • Put fish in smoker when air temperature is 100° F (you need a second thermometer to measure this). • During smoking, air temperature should rise to 225° F. • Fish flesh should reach 180° F and be kept there for 30 minutes. • Fish smoked must be stored in refrigerator. Use within one month. • Smoked fish can be canned as well.