Dehydration is an important method of preservation of fruits and vegetables. Rapid, on farm drying of these commodities offers many advantages. Most fruits and vegetables contain between 80 and 95 per cent water. Drying thus results in considerable weight and volume reduction with the consequent saving in cost of transport.

Scientists at the Centre for Application of Science and Technology to Rural Areas (ASTRA) at the Indian Institute of Science in Bangalore with financial and manpower help from Karnataka Sate Council for Science and Technology have successfully developed and field tested at fifteen locations a fuel efficient biomas burning Tray drier. Some of these driers were used successfully for drying cardamom and processed cocoa beans. ASTRA drier is a batch tray drier consisting of a cabinet for housing odd number of trays, an efficient stove for burning the biomass fuel, products for conveying the gases through various positions in the drier and ports at the bottom portion to suck in the drying air which flows up the drier in an ordered fashion over the flue ducts and tray by natural convection. Experiments carried out indicate that the drier can successfully used for dehydrating fruits, vegetables and medicinal plants. The materials dried include grape, banana, mango slices, and juice, jackfruit, coconut (for making half and full copra and dry grated coconut), tomato, potato, cabbage, carrot, onion, garlic, greens (fenugreek, curry leaves, coriander, mint), mushroom, leaves of medicinal plants. The moisture evaporated with 1 kg of fuelwood in the latest version is about 2 kg for banana, 3.5 kg for tomato and potato and 4 kg for onions.

There is also potential for application of ASTRA driers in the silk reeling industry for drying and stifling cocoons and for drying the pupa which remain after the completion of reeling. The concepts used in the development of fuel efficient ASTRA drier have been also successfully utilized in flue curing Virginia tobacco where the requirement of fuelwood for obtaining 1 kilogram of cured tobacco has been brought down to 3 kg from 6-12 kg.

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