Small-scale farmers can increase shelf-life of fruits and vegetables for up to nine days by storing their produce in simple non-energy reliant cooling chambers.
A zero energy cool chamber does not demand any form of power to run, making it appropriate for off-the grid farmers.
The structure, which is build by locally available material, relies on the principle of evaporative cooling.
Materials required include bricks, river-bed sand, bamboo and water. Two parallel brick walls are constructed in form of a rectangle above the ground. Sand is filled into the cavity between the two walls.
A standard small-scale unit can be constructed with measurements of 165 cm by 115 cm floor. Erect a cavity of 67.5 cm high-leaving an inter-space of 7.5cm. Drench the river-bed-sand- filled cavity with water.
Make a cover lid of bamboo with straws of grass.
How it works
Evaporative cooling occurs when air, which is not saturated with water, passes over a wet place. This cools the sand-bed of the cooling chamber.
As water evaporates from the bed, it causes a cooling effect. Faster rates of evaporation lead to greater cooling.
Cooling in the produce happens because water consumes energy to change to gaseous state. This means energy that could have facilitated metabolism in the fruits or vegetables is used up.
Cooling chambers can reduce temperature to between 10 degree Celsius and 15 degrees Celsius. And humidity would be kept well above 90 per cent.
Low humidity air sucks a lot of water from the system. Increased humidity causes drop in temperatures due to low metabolism in the foods because of inactivity of enzymes.
Active enzymes cause more ripening and deterioration of the skin of fruits.
Tests have confirmed that freshly harvested fruits can remains strong-skinned for six days while ripe ones would be marketable for three more days.
Morning and evening watering of the structure is important to keep the moisture content constant. It works like a refrigerator.
A few farmers in Eastern regions are using this method to maintain freshness and firmness of mangoes.
Fruits ad vegetables have to be kept in perforated polythene bags. Further information is available on the On-Farm Storage Technology manual by the Amity University Uttar Pradesh.
Food and Agricultural Orgnisation says more than 40 per cent of farm fresh produce goes bad for being perishable.