In India, about 30 per cent of coconut production goes for producing copra for oil extraction while the remaining is used for edible oil, tender coconut and for producing other value-added products.

Though only 30 per cent of the coconut goes for oil extraction, the farm level price of coconut is purely based on the oil price, resulting in unstable revenue to the coconut farmers.

The conventional method of copra drying is by spreading the split coconuts on open surface for sun-drying. This takes 6-8 days for drying and quality deterioration due to deposition of dirt, dust and microbial contamination of wet kernel is unavoidable.

Artificial method

During monsoon, drying by artificial method is the only solution for copra making. The direct-type kiln dryers are not desirable, as the copra becomes inferior in quality due to the smoking and improper drying.

The production of copra using the solar tunnel dryer is an improved and effective method, which addresses the drawbacks associated with open sun drying and kiln-drying.

A community model solar tunnel dryer of size 4m x 10m with 3m height at the center was designed and constructed at Negamam village in Coimbatore district.

A semi-circular roof portion of the dryer was covered with 200 micron UV stabilized polyethylene film. Exhaust fans, one each at front and rear end were fixed. Three exhaust vents with adjustable butterfly valves have been provided at the top of the roof for the flow of moist air by natural convection.

Three-tier metallic racks for keeping the coconut in layers during drying are provided inside the dryer.

The unit has the capacity of drying 5,000 nuts in one batch. The temperature inside the solar tunnel dryer was found to be 20-25ºC more than the ambient temperature.

The quality of copra obtained from solar tunnel dryer was superior as compared to the copra produced from open sun drying. The dryer can also be used for drying of any other commodities like chilli, spices, groundnut, sago, coir pith etc.

Dr. V. V. Sreenarayanan S. Ayyappan

& N. Muthukannan

Dr. Mahalingam College of Engineering & Technology, Pollachi, Tamil Nadu