A range of technologies are used for food drying which include tray and tunnel dryers, spray, roller and freeze dryers. With the exception of tray dryers none of these are appropriate, in terms of cost and output, for use by small and medium enterprises.
While sun drying on trays or in solar dryers can be considered as tray drying the term is normally applied to small industrial systems with some form of air heater and a fan to pass air over the product being dried. While small tray dryers are available from Europe and the USA, where they are used in pilot plants and Universities, their cost makes them unaffordable and un-economic for producers in developing countries.
In the early 1980’s; the need for small, controllable, powered tray dryers capable of producing high quality products that could be constructed by engineers in developing countries to a great extent from locally available materials. The required basic development work was carried out and there are now tray dryers, based on the principles developed by some company, in some eight countries. The greatest up-take of the technology has been in Latin America where probably over 100 units are now operational. The key point to bear in mind when considering the local construction of such a dryer is to understand the basic principles involved and adapt them to local conditions such as the dimensions of local plywood sheet, common stock steel sizes, social conditions and fuel availability.