drying of fish
TRANSCRIPT
Drying of Fish
Surendraraj
Drying-Introduction
Drying-Concentrated Food– less costly to produce, – processing equipment is limited, – storage area required is less and – distribution costs are minimum
Drying Vs Immobilization of waterPrinciple:Water removal and reduction in water activity
Water activity Vs Preservation
Theory of Drying– Evaporation– Movement of water
Food Material– adsorption layer-Bound water – diffusion layer –Less tightly– free layer –Free layer
Two phases of drying– Constant rate of drying– Falling rate of drying
Theory of DryingConstant Rate of Drying-Evaporation
Air velocityRelative humidityTemperatureSurface areaProduct Thinkness
Falling Rate of Drying-Diffusion-capillary flow of water-viscous flow of water vapour-thermal diffusion-surface diffusion in a porous medium.-gaseous diffusion-molecular diffusion in a soild medium
Factors:vapor pressure, moisture content, chemical potential Fat, Thickness, Water content
Water Activity• Water activity is the measure of water available in a food to
support microbial growth and chemical reactions• Moisture content is measure of total moisture always higher
as bound water, salt, sugar moisture not available for microbe• expressed as a fraction in the range 0-1 or usual 0-100%
percentage range used for relative humidity• Aw = P/Psat• Where P is the vapour pressure of water vapor in air that is in
equilibrium with the food sample, and Psat is the saturation vapor pressure of water at the same temperature.
Method of DryingNatural or drying
• Drying on the ground• Rack Drying• Scoffolding• Solar Tent Drying• Solar Collector Drying• Solar Cabinet Dryer
Artificial or dehydration
Heat by hot gas/Hot air dryer• Kilns• Cabinet dryer• Tunnel dryer• Multi deck• Fluidized bed dryer
Heat by solid surface/Contact Dryer
• Drum dryer• Vacuum dryer
Drying on ground
Drying on ground
Drying on Raised Platform
Drying on paddy straw
Drying on mat
Drying on mat
Drying on Mat
Drying on mat
Drying on Mat
Drying on tray
Drying on rack
Drying by hanging
Drying by hanging
Bombay Duck Drying/Scoffolding
Bombay duck drying
Bombay Duck Drying
Bombay Duck Drying
Drying on Rack
Solar Tent Dryer
Solar Tent Dryer
Solar Collector Dryer
Solar Cabinet Dryer
Method of DryingNatural or drying
• Drying on the ground• Rack Drying• Scoffolding• Solar Tent Drying• Solar Collector Drying• Solar Cabinet Dryer
Artificial or dehydration
Heat by hot gas/Hot air dryer• Kilns• Cabinet dryer• Tunnel dryer• Multi deck• Fluidized bed dryer
Heat by solid surface/Contact Dryer
• Drum dryer• Vacuum dryer
Cabinet Dryer
Tunnel Dryer• Long tunnels, 10-15 m long• Trolleys loaded with fish are moved• parallel flow drying tunnel-air towards the
outlet side cool and humid-product not dried• Counter flow drying tunnel-prolonged drying
schedules-lead to spoilage• Provide umidification and humidity control
Fluidized bed dryer
• The product is passed on a perforated conveyor bed
• Air is passed below, • Product is partially lifted and three
dimensional drying
Vacuum Dryer
• Hollow shelves, through which the heating medium is circulated in a chamber
• Vacuum will be drawn and drying will proceed under vacuum
• Expensive• Suitable for fatty fishes
Rotary Dryers
• Mainly for fish meal• Hot air from steam jacket supplied to drum• Types: Rotary drum dryer, direct rotary dryer,
indirect rotary dryer and Steam dryer
Drum Dryers
• Fluid Materials• Drum heated• Dried material scrapped off• Types: single drum dryer, double drum drier,
and twin drum dryer