Ugandan Designs Food Dryer

By Vision Reporter

Added 24th September 2002 03:00 AM

We all need food and always look for methods of preserving it the best way we know.

By Raphael Okello
We all need food and always look for methods of preserving it the best way we know.
Otim, an engineer with radio Butebo, with his son Joseph Ochuli have achieved this. They have successfully designed a fruit dryer with a capacity of 56kg of sliced fruit.
He explains that a variety of fruits such as matooke, pawpaws and bananas can be dried in the Bunch Tray Fruit Dryer. “We came up with this idea because we wanted to preserve and improve food quality.
During wet seasons, a lot of fruits and other foods are wasted because people do not have adequate and reliable heat source to dry them,” Otim says.
The dryer has a drying chamber containing 20 meshed trays on which chips of sliced fresh fruits are loaded. More chambers can be assembled to increase capacity. He says the quality of the dried fruit is guaranteed when the fruit slices are cut in dimensions of 2mm.“Slices bigger than 2mm never dry inside or take longer to dry. Also fruit slices should not overlap,” he advises. The drying takes about 4.5 hours fuelled either by sawdust or firewood stuffed in the heat source.
The rectangular heat source supplies the heat exchanger with heat through a metallic pipe. The fan blows air into the heat exchanger where heat and smoke are separated. The smoke is let out through a chimney attached to the exchanger while the refined hot air is blown into the chamber box. “Without the fan, it would be much slower although not all dryers must have fans,” he says. They used a heat exchanger, a cylindrical jet-like feature, with a fairly exposed fan at the rear to let in the air from outside. Either electricity or battery may be used to power the fan. “The design of the heat exchanger is my own creation but I adopted the appearance of the jet air heat exchanger,” Otim explains. “Air is imperative in the drying process and the fan provides the required quantity and velocity to speed up the process,” he says. “Without it, the process becomes slower. However, not all dryers must have fans. He cites the example of solar dryers. There is a regulated heat temperature required to dry each type of fruit. This helps to maintain the recommended degree of critical moisture content below which bacteria may not be able to cause infection. Therefore temperature levels must keenly be observed. “If the standard heat required to dry a particular fruit is exceeded, the quality of the output becomes inferior,” he says.
“That is why food scientists set heat standards for specific fruits.” To take care of this intricate scientific principle, a thermostat is attached to the chamber box. “The thermometer and thermostat regulate heat supplied in the chamber box,” he says.
“Once temperatures sore beyond the required degree, the thermostat automatically stops heat supply into the chamber box by releasing the metal flap in the pipe so as to block heat passage and vice versa.”
This sequence is followed all through for four and a half hours when the drying should be completed. There is no heat loss. Otim’s dryer was commissioned by the Food Science and Technology Department of Makerere University.

Ugandan Designs Food Dryer

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