Fresh 'n juicy

Friday 15 August 1997

A low-cost cooling chamber increases the shelf life of fresh fruits and vegetables and prevents weight loss

a low-cost cooling chamber that increases the shelf life of fresh fruits and vegetables has been developed by Susanta K Roy and his team at the Division of Fruits and Horticulture Technology at the Indian Agricultural Research Institute, New Delhi ( Science Reporter , Vol 34, No 6).

Even though India is the largest producer of fruits in the world and the second largest of vegetables - second only to China - 20 to 40 per cent of the produce is lost due lack of proper storage facilities. One reason is that farmers in rural India, do not have access to refrigeration .

This small zero-energy cool chamber that can be built anywhere near farms using locally available materials. The low-cost cool chamber works on the same principle which keeps water in earthen pots cool. According to this principle, when dry air comes in contact with or is blown across a wet surface, water evaporates and produces a cooling effect.To achieve this effect, the cool chamber has a wet, porous bed from where air passes through causing cooling by evaporation of water.

The cool chamber is a double-walled chamber of bricks, sand and bamboo which are kept wet. The evaporative cooling effect reduces the temperature inside the chamber by as much as 18 c and keeps the relative humidity above 90 per cent during peak summer. It has been tried out at Hisar in Haryana, Dapoli and Rahuri in Maharashtra, Kalyani in West Bengal, Solan in Himachal Pradesh, Sabour in Bihar, and in Hyderabad and Bangalore.

Encouraged by the results of the small cool chamber, Roy has developed a bigger version with a capacity of about six to eight tonnes. It has a double-layered brick wall with the cavity filled with river-bed sand. The bottom of the chamber is provided with four ducts coming from each wall and meeting at the centre. The floor of the chamber is made of wooden planks containing holes for entry of fresh air into the chamber. The roof of the chamber is made of concrete and has an exhaust fan at the centre for better ventilation. The walls of the chamber which are kept damp form an overhead tank. The duct at the base is also submerged in wet sand. As a result the hot air which enters the chamber and passes through the duct gets considerably cooled.

Roy's cool chamber is simple to construct and except for an exhaust fan and a light bulb it hardly requires any other electrical requirements. According to him the cost of the cool chamber can be brought down further by the use of alternative materials in the place of the wooden planks. However, the cool chamber requires a constant supply of water since the walls have to be kept wet. This could be a major drawback for areas facing chronic shortage of water.

The cool chamber works effectively in the dry northern plains where summer temperatures go as high as 45 c. Even under such conditions the temperature inside the cool chamber does not go beyond 28-29 c. However, it may not be as effective in the coastal areas where the relative humidity is high. Such cheap storage facilities would ensure that the highly perishable horticultural produce do not spoil and thus fetch a higher marker price.

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