Fish Products and Byproducts Technology

Unit 3- Salting and Drying

3.2.3.a. Natural drying
Sun drying
Sun drying depends heavily on the natural weather conditions since the fish is dried by heat from the sun and the air current carries the water away. Here there is no control over the operations and many a time and losses cannot be substantiated. Hence it is necessary that the operations to be controlled to get a product, which has an extended shelf life, but at the time the texture, taste and flavour is maintained. It is here that artificial driers where processing parameters are controlled gain a lot of importance. Such products have advantages over sun-dried products since they have better keeping quality and longer shelf life.
Natural Drying
Sun drying can also be called as natural drying. In this type solar and wind energies are utilized as the energy source. Some of the essential requirements for production of high quality dried fish by natural drying in the tropics are:

• Sufficiently high air temperature in the range 35-40oC will be ideal. In many tropical countries temperature often becomes higher.
• Sufficiently low RH to permit drying fish to an a level not conducive for bacterial spoilage. RH above 70-75% will not help dry the fish to the desired level. Salted fish will tend absorb moisture from the surrounding air if the RH rises above 75%. In coastal regions the humidity will be often very high limiting the speed of drying.
• Use of raised platforms. Air movement at ground levels is comparatively slow. Better air movement can be ensured if the fish is kept raised by about one meter above the ground.
• Use of drying racks. Keeping the fish on racks kept above ground level will facilitate movement of air both under and over the fish, thus allowing drying from both upper and lower surfaces. Contamination of fish by dust or sand also will be minimized. Racks with sloping tops will allow for easy draining of any surplus water on fish surfaces in the beginning of drying.

Drying on the ground
In sun drying fish is conventionally dried on sand. This sort of drying gives a product, which is contaminated with sand, filth and other foreign matters. To reduce the contamination fish can be dried on coir mats, cement platforms, bamboo mats and jute sacks. Fish dried on cement platforms gets partially cooked due to the excessive heat. It also becomes necessary that the fish turned over often to ensure a uniform dried material.
Rack drying
The most hygienic method for sun drying fish is drying them on racks. Here the fish is dried on raised racks above the ground. This can be made by tying old webbings to poles made of locally available materials, which are fixed at specific distances from each other. This ensures circulation of air from both top and bottom and contamination of the product with sand or dust is almost completely avoided and a quality product is assured. Here the rack can be sloping type where there is a drain of the water, or it can be a multideck rack that consists of two layer, or more.