Research Body Develops Modern Solar Fruit Dryer

Thursday, January 26, 2006

A new highly effective solar dryer for reducing the massive post-harvest losses of fresh produce has been adopted by farmers in Wakiso district.

The dryer has been developed by Uganda Industrial Research Organisation with support from the German Technical Cooperation and the Ministry of Energy and Mineral Development.

Farmers in Wakiso are optimistic that their fruit production will increase after several years of making losses.

Uganda grows a variety of crops ranging from cereals, fruits, vegetables, legumes, beverages and oil seeds, which are ideal for foreign markets.

Unfortunately, most of the produce has low market value and makes heavy losses after harvest.

The losses are estimated at 10-20% in cereals and grain legumes and 25-30% in semi-perishable crops.

Such produce could have been processed to increase its shelf life, safety and market value, and sold on both the local and foreign market.

However, this could not happen because of the lack of a well-defined mechanism to solve the problem.

The rocket elbow solar dryer dries 11% of the water in fruit chips, limiting their rotting.

Unlike other dryers, it takes less time and consumes less energy.

It can be used to dry pineapples, bananas, pawpaws and other fruits and thus increase their shelf life.

“Uganda experiences some of the highest losses in the agricultural sector in Africa due to poor post-harvest handling technology.

About 30% of the produce is lost annually,” indicates the Uganda Science Journal which was released recently.

Moses Kiyimba, one of the farmers who have benefited from the dryer, says it uses both solar and wood energy.

He notes that due to variations in temperature, solar may not be enough for drying the produce during some seasons.

Kiyimba said the machine can dry a tonne of fresh fruits using only 40 kilogrammes of wood in about 12 hours.

It has about 15 square metres of drying area, with wooden trays where the fruits are put for drying.

“The dryer can be constructed using locally available materials. It’s a permanent structure that costs sh1.5m to construct. It is suitable for someone in the export business or a person who dries fruits on a regular basis,” Kiyimba said.

The dryer has an absorber for sunlight with a black surface filled with black paste. The absorber is covered with clear glass to let the sun heat the black paste. When the air is heated, it is sucked inside by a fan in the middle of the stove.

The air then moves over the heated pipes and reaches the fruit being dried before evaporating into a furnace at the top of the dried produce. The dryer heats to about 800 degrees centigrade.

The pipes are heated to enable the hot air reaching the fruits dry the chips faster.

The fan is always on to push the air to the heat exchanger with pipes that are heated by hot exhaust gases from the stove.

The dryer heats the fruits to refined export quality levels. Smoke does not mix with the fruits.

The researchers said they wanted to make air distribution inside the dryer even all the time.

Godfrey Lubwama is in charge of the dryer. Got in April 2005, it has excited most of the farmers engaged in fruit production.

He said the dryer has 24 trays with a carrying capacity of two kilogrammes of sliced pineapples and two bunches of bananas per tray. The fruits take three days in the dryer.

Source: New Vision (Kampala), Ronald Kalyango (link opens in a new window)