Fish products and Byproducts Technology

Unit 3- Salting and Drying

3.2.3.b.Solar Drying
Harnessing the solar radiation for solar powered driers has, of late, attracted considerable interest because of the absence of any energy cost and possibility of producing a dry fish in good hygienic condition even when the RH is high. Energy of the sun is collected and concentrated to produce elevated temperatures suitable for drying several commodities including fish. When the temperature of the air is raised, its RH will be reduced; in other terms its capacity to hold water will increase and hence, can absorb additional quantities of vapour.
Solar Tent Dryer
One of the simplest forms of driers to use solar energy for drying fish is the solar tent drier. This is working on the principle that a black surface absorbs sun’s energy for more effectively than any light colored surface. The air thus heated is allowed to pass through the fish and escape our through a vent in the top simultaneously admitting fresh air inside through a vent provided at the bottom of the tent. Polythene tent drier is used to serve this purpose.
In a solar tent drier, the air temperature is known to rise to the levels of 60oC or more in tropical climate. This will adversely affect the nutritional as well as physical properties of fish and is considered a disadvantage. However, compared to normal sun drying solar drying has the following advantages:

• no energy cost
• very low equipment cost
• shorter drying periods
• no contamination from dust, insects
• Produces hygienic product with low moisture content.

Solar Collector Dryer
Here the solar energy is first collected in the solar collector chamber. The heated air is then passed through the drying chamber, where the fresh fishes are kept for drying on plastic mesh/trays. The hot humid air will escape through the chimney. Clear polythene sheet covers upper side of dryer, where as the floor of the dryer is spread with black PVC sheet. The rack for fish spreading and drying is made up of black plastic mesh.
Solar cabinet dryer
This is a rectangular shaped dryer made up of plywood. The front side of the dryer is double walled. Inlet and outlet are provided for air to enter and escape from the chamber. A clear polythene sheet covers the upper portion of the drier. Two doors are present for loading and unloading the fish into the drier.