Fish kept shaded will be cooler than if they are exposed to the sun. Keeping the surface of the fish wet will help bring the temperature down evaporation of the water absorbs heat from the fish. It is easier to keep the fish damp if materials such as wet seaweed, leaves, sacking, or sawdust are used as a light covering to increase the amount of water available for evaporation.
Whether the fish are stowed with ice or without, overfilling of containers should be avoided to prevent crushing them figure 5. Spoilage can never be prevented through chilling or cooling, but the cooler the fish are, the greater the reduction in bacterial and enzymatic degradation. In some areas, work has been done on ice-making machines that do not require gasoline, diesel oil, or electricity as an energy source.
A biomass-fueled ice-making machine has been developed at the Asian Institute of Technology in Thailand. It requires little maintenance and has no moving parts. Almost any waste biomass can serve as the fuel figure 5.
This ice maker uses an intermit- tent ammonia-water absorption cycle. These refrigeration systems produce their cooling effect through the heat absorbed when liquid ammonia Is converted to gaseous ammonia.
As liquid ammonia vaporizes, heat is extracted from its surroundings. When this. As seen in figure 5. The ammonia is clis- tilled out of the water mixture, passes through the liquid seal C , and is cooled to liquid ammonia in the condenser coil D. The liquid ammonia is held in the ammonia receiver E. To make ice, the liquid ammonia is released into the ice box F where it reverts to gaseous ammonia and converts containers of water to ice.
The gaseous ammonia is then redissolved in water in the generator B and the cycle can start over. The complete cycle takes about 12 hours and produces about kg of ice. A compact solar refrigeration system that uses the same tech- nology as the biomass-fueled ice-making machine has also been developed figure 5. In this case, the ammonia-water solution is heated in the pipes of a solar collector. It has been successfully field tested in Khan Yai, a remote rural island off southern Thailand.
However, to ensure a high-quality finished product, it is necessary to begin with a high-quality raw product. This, once again, accentuates the importance of primary processes.
Silting Whether an end in itself, or as part of a smoking or drying process, salting has been used for thousands of years to preserve marine products. Salting has no adverse effect on the value of fish protein.
Bacterial growth can be significantly retarded by the presence of sufficient quantities of common salt sodium chloride. When fish is placed in a brine solution, the salt penetrates the fish, and water is extracted from the tissues by osmosis. At a salt concentration of percent in the fish, the activity of most bacteria that cause spoilage will be inhibited.
The higher the salt concentration in the fish, the. Several methods of salting are cornrnonly used: dry salting, kench salting, brine salting, and pickle salting.
Dry salting is the simplest method and is used primarily for fish with high water content. Granular salt is rubbed onto the outer and inner surfaces of the fish. Kench salting is a similar method that involves stacking split fish and layers of salt.
The pickle or liquid formed is allowed to drain. In Brazil and India, sardines are preserved by pressing and salting. Avoiding air expo- sure is almost unpossible in these dry-salting processes. The wet-salting methods brine and pickle are recommended for tropical applications, especially with fatty fish.
In brine salting, the entire or split fish is immersed in an aqueous salt solution. For strongly cured fish, about 30 g of salt per g of fish is needed. During processing, the brine solution will become diluted as water is drawn from the fish, and.
Plastic or wooden barrels can be used for brine treatment. The largest fish should be able to lie flat in the container. A wooden lid, which can be weighted, should be employed to ensure that the fish are submerged in the brine solution.
Another wet cure is pickle salting. The fish are covered with salt and placed in layers with salt between the layers. Since a watertight container is used, the brine that is formed begins to cover the fish. A lid is placed over the fish to ensure that they are completely submerged in the liquid. Halophilic or salt-tolerant bacteria or molds may grow on in- completely dried salted fish or on dry salted fish that have become moist.
However, pickle-cured fish are free of growths of halophiles, because these organisms are aerobic, and the brine of pickle-cured fish does not contain sufficient oxygen to support their growth. This oxygen-poor environment also reduces rancidity in fatty fish. Drylllg Much of the fish in rural areas of the tropics Is preserved by sun drying. While the cost of sun drying is low, there are significant losses due to spoilage, contamination by dust, and insect infestation, particularly when the fish are laid close to the ground.
As a first step, raised structures would reduce contamination from some wastes and insects. Solar fish driers are simple and inexpensive and can eliminate much of the spoilage that occurs with traditional drying methods. These driers usually have a wood or bamboo-frame table, covered with plastic or glass to produce an enclosed chamber figure 5.
The surface of the table can be covered with black plastic or paint to absorb the sun's heat. With openings at the top and bottom of the drier, air will be heated and flow around the fish. Fish exposed to this flow of heated air will rapidly lose moisture, reducing drying time by as much as half over open-air drying. Solar driers have a number of advantages over traditional drying methods. They exclude rain, insects, animals, and dirt, and can produce.
Doe temperatures blab enough to reduce the posslblUty of mold or bacteria spoilage. An oil drum solar drier has a creative design figure 5.
The ends of the drum are removed and three rectangular ports are cut in the side. The drum is mounted on a wooden frame that includes air vents and access doors on both ends of the drum. Two sheets of clear plastic enclose the drum. These allow sunlight to heat the drum and, because of the air space between the two sheets, provide insulation to retain the heat. The outside of the drum is painted black to absorb solar radiation and the inside is painted white.
This heated air then enters the drum through the rectangular ports and passes over the trays of fish in the drum and out through the vents at the ends of the drier. When in use, fish are placed on the bamboo supports and transparent plastic covers the top.
A mud wall solar drier has been developed in Tanzania. The bamboo tubes have a number of small holes so that air can flow into the drier. Fish trays are placed on top of the bamboo tubes and openings are cut into the top edge of the wall to exhaust the heated air. The inside walls and bottom of the drier are plastered with mud that is mixed with charcoal powder to absorb the heat.
In addition, a layer of dark-colored stones can be placed in the bottom of the dryer to provide heat storage. The roof can be a transparent plastic sheet or film. A solar dome dryer figure 5. Designed on the basis of results with solar tent driers, this large unit has a capacity of about 1 ton of prepared fish.
Use of the solar dome dryer also significantly reduced contamination from insects, animals, and dust. A solar collector can also be attached to a cabinet drier figure 5.
The solar plate collector uses black coated, corrugated metal to absorb the radiation. This is covered by a double panel of glass. Or plastic to insulate the warm air inside the collector. Air passes on both sides of the metal collector, becomes heated, and flows into the upright cabinet drier and through the trays. The solar agrowaste-fueled drier was designed and constructed in the Philippines figure 5.
It has the advantage of utilizing alternative energy resources in the absence of solar heat. The drier has both a solar booster and furnace. The body of the drier is trapezoidal and is made of wood or aluminum frames covered with polyacetate film.
Black film covers the bottom of the drier. The side walls have up to 4 doors that allow 14 trays x 53 cm to slide into the drier. Woven nylon screen is used to line the bottom of the trays. The top portion of the back wall has several screened warm-air outlets. A small stove can be connected to the drier. Charcoal or agricultural waste materials can be used as fuels in the stove furnace.
Warm air from the stove is regulated with a shutter so that only heat enters the unit while fumes are excluded. The solar system may be used alone or simultaneously with the stove. Alternatively, the agrowaste system may be operated alone in the absence of solar heat or solar heat can be used during the day and agrowaste drying at night.
Other models of low-cost fish driers use only agrowaste as fuel. The agrowaste fish drier figure 5. The trays in the drier can hold up to kg of fresh fish. At the base of the structure is a furnace made of hollow blocks, with inside dimensions of 0. An exhaust tube carries smoke and gases outside the system. The furnace and drying chamber are separated by a corrugated, galvanized iron heat guard.
Smoke contains substances that kid bacteria, thus helping to preserve the product. The heat also dries the fish. Often fish are salted before they are smoked. In tropical countries, fish are generally heavily smoked at relatively high temperatures so that they are also cooked.
This is usually long enough to eliminate the non- sporulating spoilage bacteria. However, the spores of Bacillus sublil" and B. The bactericidal action of the smoke is considerably increased by the presence of salt in the fish. In simple smokers, fish are laid on trays or hung in the column of smoky air above the fire.
The traditional Ghanaian mud oven Is cylindrical, with a thatched cover figure 5. The oven consists of layers of mud about 2. Grill bars are installed at about 1 m off the ground.
The fish, placed on the grill bars, must be regularly turned to encourage even drying and smoking. A stokehole is located in the base wall. The drums are cut along their length and rejoined to form a larger cylinder.
Fish are smoked on grills within this cylinder. The Ivory Coast kiln figure 5. Most fishing in India is carried out within a distance of about seven miles from land; the boats remain at sea for a few hours and return to port on the same day. Like the salting method, it lowers the water content of the fish to a point where microorganisms, bacteria, enzymes, and yeasts cannot grow and multiply.
The most popular fish preservation method is solar drying. It is done in combination with salting. Fish dried under the sun look and taste better. Steps in Drying. Wash the fish thoroughly. The primary objective of food preservation is to prevent or slow down the growth of micro-organisms including moulds, yeasts and bacteria as the growth of these micro-organisms causes spoilage of food.
Food Preservation Methods 1. If you are new to the world of food preservation, this might be a great place to start. You'll need a food dehydrator and that is about it. So as you can tell, this method is pretty basic. You'll just lay the food in the dehydrator and wait until it is completely dried. Like meat, fish and other seafood may be spoiled by autolysis, oxidation or most commonly by microorganisms.
Smoking is usually done through four processes. First is cleaning the fish. Second is brining which is soaking the fish in a brine solution. The third is drying and the fourth one is smoking the fish. In smoking process, the length of smoking time usually takes up to 30 to 45 minutes and the temperature is 85 degree Celsius.
Hardwoods together with plant leaves are commonly used. Pickling and spicing; this method in fish preservation used vinegar and other spices. The growth of bacteria and other organisms is prevented by the acetic acid of the vinegar; the vinegar will preserve the fish as well as improves its taste. Canning is another method in fish preservation. It is the process of preservation that uses hermetically sealed containers such as bottles or cans.
The procedure of heating the fish before and after canning can kill bacteria and other microorganisms that can cause fish spoilage. Turn this call to action on or off. Link this call-to-action to a page or your choice.
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