SALTING AND DRYING THEORY OF SALTING AND DRYING

SALTING AND DRYING

THEORY OF SALTING AND DRYING THEORY OF SALTING Salting is preservation of fish with dry edible salt. Salt absorbs much of water from food and makes it difficult for micro – organisms to survive. Salt delays the activity of bacteria or even inactivate them by lowering the water activity.

THEORY OF DRYING AND DEHYDRATION DRYING • Drying is one of the oldest method of preservation of food. • Drying refers to “Sun drying” where fish is dries under open air using solar energy to evaporate water in the fish. • The evaporated water is carried out by natural currents

DEHYDRATION A process of drying under controlled operational parameters like temperature, air velocity and relative humidity is known as dehydration. It is carried out in enclosed atmosphere with facilities to control operational parameters.

METHODS OF SALTING DRY SALTING Dressed fish is mixed with crystalline salt in containers. Salt and fish are spread in alternate layers, the proportion of salt increasing upwards. Fish is allowed to remain in brine for 2 – 3 days and dried afterwards KENCH SALTING A method of dry salting except that the self – brine formed is allowed to drain off. KENCH SALTING

BRINE SALTING In this method of salting, fish is kept immersed in the in brine of desired concentration for the required time. This a preliminary step to smoking and canning MIXED SALTING PICKLE CURING An advantageous method over brine salting for large and oily fishes is mixed or “Pickle curing”. Fish is mixed with dried salt and packed in watertight containers with salt sprinkled in each layer.

METHODS OF DRYING NATURAL DRYING Solar and wind engines are made use of in natural and drying process. High temperature (35 - 40 °C), low Relative Humidity (< 70 – 75%), raised Platforms and drying racks are required for natural drying MECHANICAL DRYI NG There are two types of mechanical drying: In one type, heat is transferred to product through hot air/ gas usually air. In another type, heat is transferred to the product through a solid surface.

MECHANICAL DRYING Drying through hot gas Cabinet Drier Drying through a solid surface Drum Drier Kiln Drier Tunnel Drier Spray Drier Vacuum Shelf Drier

Cabinet Drier Consist of insulated or non – insulated framed structure with trays where material is spread. Fan is located inside to blow air as ah heat source over the material Kiln Drier KILN DRIER It is a type of batch drier with two - story building The floor of upper story is made up of slats on which material is spread The burners or furnace producing hot gas is placed on the lower floor.

Tunnel Drier Commonly used for drying fish These are made in form of long tunnels, 10 – 15 m long. Trollys loaded with trays containing fish are moved into the tunnel Hot air is blown over the material across the trays Spray drier It is used for drying foods which are in liquid or suspension form Food in liquid is suspended in a stream of hot air in a chamber where it gets rapidly dried

Drum Drier In drum drier heat is transferred to the product through solid surface. It is used for drying fluid materials. Fluid is deposited over the drum as thin film, and drum is heated by steam, while it is being rotated. Vacuum Shelf Drier It consists of vacuum tight chamber with access door and outlet for gases and vapours. Vacuum will be drawn inside the chamber through the vapour outlet, and drying will be proceeded under vacuum.

SPOILAGE IN SALTED FISH “Pink or Red” This occurs in salting during storage at warm weather conditions where surface of fish becomes covered with red slime. It is caused by halophilic rods and cocci originating from salt. They include Halobacterium salinaria, Sarcina morrhuae, S. littoralis, Micrococcus resens Prevention: Storage of fish at low temperature Moulds grow at RH of 75 % or more. “Dun” is a type of mould development in heavily salted fish. Give appearance as if sprinkled with ground black pepper. Preservation: low temperature storage and use of good quality salt

SAPONIFICATON Damage caused by aerobic microorganisms active at low temperature. It results in malodorous slime on the surface of fish. Prevention: Fish can be kept in brine containing vinegar and water. PUTREFACTIVE SPOILAGE Slow salting process cause this spoilage which cause flesh near backbone to become tanned or reddened with offensive odour. Preservation: Any pre salting operation that can accelerate the salting

Infestation by maggots: Cheese flies (Drosophila casei) are attracted to drying fish by bits smelland unhygienic atmosphere Rust: appearance of colour similar to rusting of iron on the surface o fish is Rust Generally occur in oily fishes like Sardine and Mackerel by the oxidation of oil in fish due to atmospheric oxygen. White spots: presence of Calcium and Magnesium in salt cause whitening in flesh. Fragmentation: Cured and dried fish becomes brittle and break during storage and transportation.

SPOILAGE IN DRIED FISH MOULDS: Moulds can grow on salted or unsalted dried fish if the moisture content is high and RH is above 75%. It increases surface moisture owing to other types of spoilage. INSECT INFESTATION: Unsalted dried fish are often infested with Brownflies, Chrysomya Spp. , Lucilia Spp. , Sarcophaga Spp. Etc. Pesence of salt can reduce the activity. RANCIDITY: Fatty fish, are prone to oxidation and development of rancid flavour. Airtight packaging can control rancidity.

QUALITY STANDARDS FOR CURED FISH PRODUCTS AS RECOMMENDED BY BUREAU OF INDIAN STANDARDS Sl. No. PRODUCT MOISTURE(%) SODIUM CHLORIDE (%) BY MASS OF MFB ACID INSOLUBLE ASH % BY MASS ON MFB (max. ) 1. Dry- salted catfish (a) 35 25(min) 1. 5 2. Dry- salted dhoma (b) 35 10 -15 (min) 2 3. Dry- salted Horse mackerels (Caranx spp. ) (c) 40 25 (min) 1. 5 4. Dry- salted Threadfin (Dara) (d) 40 25 (min) 1. 5 5. Dry- salted Leather – jackets (Chorinemus spp. ) 40 25 (min) 1. 5 6. Dry- salted mackerel (e) 35 25 (min) 1. 5 7. Dry- salted Jew fish (Ghol) (d) 40 25 (min) 1. 5 8. Dry- salted seer fish (f) 45 30 (min) 1. 5 9. Dry- salted shark (g) 40 25 -30 (min) 1. 5

Sl. No. PRODUCT MOISTURE(%) SODIUM CHLORIDE (%) BY MASS OF MFB ACID INSOLUBLE ASH % BY MASS ON MFB (max. ) 10. Dry – salted suirai (tuna) (h) 35 25 (min) 1. 5 Dried products 11. Dried and laminated Bombay duck (i) 15 7. 5 (max) 1. 0 12. Fish maws (j) 8 - 1. 5 13. Dried Prawn 20 5 (max) 1. 0 14. Dried shark fins 10 - 1. 5 15. Dried white baits (Stolephorus spp. ) (k) 20 2. 5 (max) 7. 0 Mfb = moisture free basis

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