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India is the second largest producer of Onion in the world, next to China, accounting for 16 % of area and 12 % of production of the world. Onion, the most widely consumed vegetable, is used for flavouring and seasoning the foods. As onion is a perishable crop, it can not be stored in normal conditions for a long time. Presently, about 40 % of the onion production is estimated to be lost in the post harvest stages in India. Therefore, in order to overcome these losses, the dehydration of onion is to be employed as one of the major processing operations which reduces the volume and thereby, transportation cost and increase the shelf life.

Further, it was observed that the existing onion dehydration plants were facing problems regarding quality of dehydrated onion especially colour, taste, texture, etc. Also, the drying time was high. Keeping the above views in mind, the research work on dehydration of onion was undertaken. Freshly harvested Talaja local, white cultivar of onion, was taken for the studies. Its physical and thermal properties were determined. A laboratory scale thin layer dryer was developed for conducting the experiments on dehydration. The effects of independent variables, namely, the drying air temperature, velocity of air and thickness of onion slice on the drying time, sensory quality, rehydration characteristics and bacterial counts were studied. The experiments were conducted according to the Central Composite Rotatable Design.

Based on the research findings, it could be recommended that the dehydration of onion (cultivar - Talaja local white ) should be carried out at 76 C drying temperature and 27 m/min velocity of air, keeping 3 mm thickness of slice to get good quality of dehydrated flakes with the lowest value of drying time (58 min).