FISH CANNING The main objective of fish canning is to yield a product that may be stored for a considerable period of time, at the end of which it will be interesting and safe to eat. Before packing, fish is cooked and then dried at suitable temperature. Fish deteriorate after death due to action of enzymes and bacteria. Both enzymes and bacteria can be permanently inactivated by heat and provided that reinfection does not occur, heat processed food can be kept indefinitely. This is the principle on which heat processing and canning is based. In order to achieve a fish pack of satisfactory keeping quality, the following conditions must be maintained:
1. Contents Contents of can can must be be sterile, sterile, that is free free from active active bacteria bacteria and enzyme enzymes. s. 2. The insid insidee surface surface of the can must be resista resistant nt to attack attack by any part of the content contentss and the outsid outsidee surface surface must must be resista resistant nt to corros corrosion ion under under reasona reasonable ble storag storagee conditions. 3. The lid lid of the can must must be sealed sealed to the the body to prev prevent ent the the entry of of air, water water and contaminants carried by these. These conditions are not fully realized in practice but nevertheless, packs are prepared where shelf life can be confidently predicted to be at least 2 years. Factors which affect suitability of a fish for a particular process: 1.
Size: Very small fish may be dried whole whereas larger fish may always be cut so as to increase the surface area available for salt penetration and or moisture loss.
2.
Oil content: Fish oils oxidize readily and become rancid. Rancidity gives a bitter flavor to the bitter product. Fish which contain much oil do not generally make good, salted and or dried products since the oil act as barrier to salt penetration and moisture loss.
3.
Flesh texture: Fish in which flesh is firm or moderately firm are easily handled. They can be cut without filling apart and dried product can be transported without breaking up. Fish which have a very soft flesh tend to tear when attempts are made to cut them and dried products are made.
Site of fish canning plant:
Following points must be taken in to consideration while choosing the site for canning plant as it controls the economy of the plant: 1. Plant should should be located located at such such a place place where where raw fish fish is availabl availablee easily. easily. 2. Water Water shou should ld be read readily ily availab available. le.
3. Market access should be there.
HANDLING OF RAW MATERIALS: Fresh fish make the best product. Hence, every effort must be made to ensure that the fish being processed are fresh. Boxing of fish in the sea has been shown to have a markedly beneficial effect on the appearance and keeping quality of fish. The fish tears in the belly region especially if the fish were feeding heavily before capture. Boxing prevents excessive pressure on the lower layers of fish by the above, which would otherwise lead to bursting of the wall. This apart form causing the fish to look unpleasant accelerates deterioration by releasing digestive juice to the surface of the surrounding fish. Preservation of raw material : 1.
By adding chemicals: If the time interval between catching and canning is not too long, some degree of preservation is achieved by sprinkling salt. Some canners use chlorine or a mixture of 3-tert-butyl-4-hydroxyanisole and 2-tert-butyl-4hydroxyanisole for short time preservation.
2.
Chilling: It is done whenever fish has to be kept for more than a few hours before canning. The proper and uninterrupted chilling improves the quality of the canned product.
3.
Freezing : whenever the time lapse between catching and canning exceed several days, bulk freezing is advisable for keeping the raw material in good condition.
FLOW CHART FOR CANNING FISH
TREATMENT OF RAW MATERIAL BEFORE CANNING: Nobbing: For small fish, dressing is restricted to removal of head and intestines. For larger fish like tuna and salmon, head and gut are removed but not the roe (firm eggs) or milt. This process of removing head and gut in one operation is called nobbing. It was previously carried out by hand but now the work is done entirely by machines capable of handling 180 fish a minute when fed by two persons. Fish are placed on endless belt which feed them to a circular cutting wheel. This partially severs the head which together with the gut is then drawn away from the body by two corrugated rollers. If desired, tails can be severed in the same operation.
Bleeding: Nobbing releases blood which must be removed because it causes brown staining in the processed fish. Tuna fish are hung after beheading and gutting to drain off the blood.
Washing: Washing removes the surface slime. Washer consists of a revolving cylinder, the lower half of which is immersed in running water. The fish are fed in at one end and tumbled about by paddles as they pass along the cylinder. Washing water should be chlorinated as chlorinated water has been proved to be efficient in removing bacteria from dressing line which may otherwise may become a dangerous source of contamination.
Brining: The main purpose of brining is to stabilize the flavor of the canned product and to bring out its characteristic taste. The fish are immersed in a concentrated solution of common salt for a predetermined period of time. Salt is absorbed by the flesh and impart a desired flavor to the product in which the salt content of 2% is acceptable. Brining toughens the skin of the fish. Brining also brightens the appearance of the fish removing any slime if present. The salt used for brining should be pure and should not contain appreciable quantities of magnesium chloride, a common contaminant of unrefined salt. A salt containing magnesium
chloride increases the risk of struvite formation. Struvite is a chemical called magnesium ammonium phosphate which sometimes forms crystals resembling bits of glass in fish cans. To ensure uniform brining, the fish should be stirred frequently. Brineometers should be used to check the salt content of the brine at frequent intervals. Brining times vary depending upon various factors. Large fish require longer time than small fish. Fatty fish also require longer brining time than leaner fish. Fish that have been filleted or split require shorter time than nobbed fish. In practice, bring times varying from 15 minutes to 45 minutes are used. Brines can be used many times over it is important to remember that there are many bacteria that are able to multiply in high concentrations of salt, especially when the solution carries the increasing quantities of oil, blood and pieces of gut. Thus brines should be changed frequently else they would become a source of contamination.
Precooking: When fish flesh is heated, a fair amount of water is released from the proteins. The amount varies depending on the fat content. Further release of water takes place during the storage of the canned product. If all this water were to remain in the can, a very unattractive pack would result. It is therefore necessary to cook the fish before it is retorted either before or after packing in to the can. Precooking is very critical process, so the fish should be heated enough so that no further exuded in the r etorting. It is generally necessary to reduce the water content of the fish to at least 60%. Tuna fish are cooked in brine while oil packed fish like sardine are precooked by immersing them in heated oil. Peanut oil is used for pre cooking and heated at 110°C for 2-3 minutes.
Drying: After brining, fishes are removed in wire mesh baskets and allowed to drain for several minutes or fish are allowed to dry in a cool air current. Tuna fish is dried for 18-24 hours for drying. Such drying should be carried in well covered ventilated places where fish is protected from contamination.
Smoking: Hot air drying may be accomplished by smoking. This imparts a desirable flavor to the canned fish in addition to removing moisture. It is used particularly for Sardine type of fish.
CANNING OPERATIONS: Filling of the can : the choice of the can used is governed by the size of fish being packed. The filling of fish in even highly mechanized plants is mostly done by hand. Cans should be washed immediately before filling as they rapidly accumulate dirt and dust during storage. In all filling operations care should be taken that no air pockets are left which cannot be removed by subsequent exhausting since they may cause swells and usually a small head space is left to hold small quantities of gases which may be generated during processing.
Addition of substances to enhance flavor: most fatty fish like tuna, salmon give acceptable products with nothing more than salt added. Non fatty fish call for special additives to improve the flavor and texture.
Brine is by far the most common additive. Wherever fish are not salted before packing, the filled can is either topped by a brine solution usually 3% or a salt pellet is added. Upon adding a salt pellet, it takes 3 days for the fish to become uniformly salted. Glutamate, sugar, oil (preferably olive oil), tomato sauce and carboxy methyl cellulose (take up water) are added to enhance the flavor and quality of the final product.
Exhausting: Small cans can be closed and processed directly. Larger cans however have to undergo one further important operation before being closed, namely exhausting. The purpose of exhausting is to produce a partial vacuum in the head space of the can which will persist after the can is heat processed and cooled. The head space of the can is the part which is not filled either with solid or liquid. When can is open, the head space is filled with a mixture of air and water vapor and if the lid is seamed on, the pressure in the head space will be equal to the outside atmospheric pressure. If the closed can is now heated, the pressure in the head space will increase as the air expands, the water evaporates in to steam and solid and liquid contents of the can expand. Gases are also given off by the fish flesh which slightly adds to the air pressure. This internal pressure forces the ends of the can outwards and may lead to swelling and distortion. As a result, the seam of the can may be strained and may leak even after it is cooled. Because small cans are mechanically stronger, they are unlikely to be harmed in this way. If while the can is still hot, a small hole is bored in the lid, air, water vapor and other gases will blow out until the pressure inside is again equal to the outside. If this hole is sealed up immediately while the can is still hot, and the can is allowed to cool, the headspace pressure will drop below that of outside atmosphere because a ir that has blown out while the can is hot cannot be replaced. This difference in pressure between the can head space and the atmosphere is called partial vacuum.
Closing the can: All fish cans are seamed by double seam method. A seal must be achieved that will prevent passage of contaminating material, carried either in air or water in to the can after it has been sterilized.
Processing and Retorting: There is only a marginal difference between the degree of heat treatment required for commercial sterilization and the amount of heat impairing the quality of final product. In order to obtain good commercial stability and to reduce the risks of undesirable changes, the optimum time temperature relationship must be established for each product and can size and for any given processing equipment. Before cans are loaded in to the retort, it is advantageous to wash them by either spraying or by dipping in hot water as fish pieces, oil or sauce adhering to the cans might contaminate the cooking water, clog the retorts and may after processing prevent the sticking of labels to the can. Usually, the cans are passed through a tank containing hot detergent such as 1-1.5%
Na3PO4 at 80°C. The washed cans should be rinsed with hot water in order to remove any detergent residues which might cause can corrosion.
Cooling: The tendency of certain fish products to produce off flavors during heat treatment necessitates rapid cooling immediately after processing. Cooling can take place inside or outside the retort. The evaporation takes place during removal of the cans from the retort to the labeling and packaging section and should be sufficient for drying the surface. Water used should be pure. As the cans are cooled, pressure inside changes rapidly and under such conditions even correctly made seam may allow the passage of trace water which if contaminated, may give rise to spoilage during subsequent storage. Chlorination of cooling water is recommended.
Labeling and boxing: After cooling, cans of large fish are stored for weeks before labeling. They are either stacked or boxed and then stacked. Labeling should not be carried out immediately after processing due to the soft nature of the fish. Storage of cans for a period allows the content to mature. Sauces, if present penetrate the flesh. For ordinary fish products, storage temperature should not exceed 20°C.
SPOILAGE IN CANNED FISH: Causes of canned fish spoilage: 1.
Precanning spoilage: insufficient pretreatment, especially inadequate cooling or improper preservation of the raw material or undue delay on the canning line previous to processing can give the microorganism causing spoilage of raw fish a chance to develop.
2.
Insufficient processing: insufficient processing leaves only a small number of heat resistant spore forming bacteria in the canned product.
3.
Can leaks: Contamination of the cans after processing can occur through leaks in the can. In contamination through leaks, any kind of bacteria can enter the can.
There are two main types of spoilage in canned fish: bacterial and chemical. Bacterial spoilage is either due to under processing or due to subsequent infection of the can contents by infected cooling water or bad seaming. Chemical spoilage is caused by the action on the can wall of various chemicals present in the fish or quite frequently, by acid sauces present in the can.
Bacterial spoilage: Bacterial spoilage of canned fish products may be divided in to two types. In one, caused mainly by anaerobic spore forming bacteria, swelling of the cans occur due to production of gases such as hydrogen and carbon dioxide. In the other type of spoilage, bacteria produce flat sours. Major defects in canned fish products can be listed as follows:
1.
Flipper: Slight positive pressure can be demonstrated by striking the can against a solid object. If one end bulges out, and returns to the original position under slight pressure, it is known as flipper.
2.
Springer: Greater pressure in the can causes formation of springer. The end of the can is permanently bulging and on pushing it back, the other end bulges.
3.
Soft Swell: Both ends are bulging but can be moved slightly by thumb pressure.
4.
Hard Swell: the internal pressure is so great that the bulging ends cannot be moved.
5.
Flat sour: No gas is produced in the cans but on opening, the contents are found to be inedible with an unpleasant flavor and odor.
Chemical spoilage: Cans are made up of tin plate which consists of mild steel sheet coated with a very thin layer of tin. For many canned goods, the tin is sufficiently unreactive to be used without any further protection. But fish products especially those containing acid sauces require cans with a second protective coat. This is a lacquer prepared from polymerized fish oil that is normally used. If there is a flaw in the lacquer, the acid attacks the tin and may penetrate to the steel. Gaseous hydrogen is formed and this may cause the can to swell. Trimethyl amine oxide plays an important role in chemical spoilage. Some fish products such as lobster, crab and shrimps form volatile sulphur stains which lead to the formation of iron or tin sulphides or both. When these products are packed, special lacquers are required. One such lacquer is called pigmented lacquer which contains zinc oxide and reacts with sulphur compounds to give a white instead of black stain and is therefore not offensive.
