Charcoal cooler for long shelf life

Farmers who grow crops such as vegetables and fruits face challenges of keeping them fresh as they head to the market. Unfavourable temperatures and unprotected storage areas increase post-harvest losses and reduce profits.

Against this backdrop, a joint research carried out by Uganda Christian University and Makerere University has yielded a charcoal-walled evaporative cooler to help farmers curb post-harvest losses and increase shelf life for vegetables and fruits. This was in partnership with Coalition for Health Agriculture and Income Network Uganda (Chain), which is the implementing agency.

Evaporative cooler
Charcoal is used because it has a porous structure that can hold water, is affordable and easily available in many places.

The cooler is a room with charcoal-laden walls. It has a wooden frame, which supports the walls and roof. The frame is covered with wire mesh separated by about 10cm with the interior being filled with charcoal.

The charcoal is on all four sides, filled in the space and leaving a gap of 15cm to 20 cm to the roof.

This space is left open to allow air circulation. The charcoal remains moist, and as warm dry air passes through, the water on the charcoal evaporates and cools the air. This keeps the room very cool.

This cooler provides a low-cost way to preserve the produce using readily available materials.

A 100-litre tank, a pump for constant water supply, charcoal, plastic or coated net, wooden poles, ventilator and tiled shelter to keep off the heat are the materials needed to complete the charcoal cooler.

The average measurements for the room are 2.5m in width, 1.5m in length and 3m high. A room this size can store leafy vegetables for up to five days, milk for four days, and vegetables/fruits such as tomatoes for up to 14 days.

Location
The site on which the cooler is to be built should be considered carefully because air movement is very important.

Evaporative coolers rely on air movement in order to be effective, thus it should not be placed where there is little or no wind.
It also requires a lot of water in order for the cooler to be operational, thus a good source of water should be close to the site.

A shade would be ideal as it would reduce the use of water as the walls will need less water and will reduce temperatures faster.
The charcoal cooler, which was tested for storing leafy vegetables and fruits, was been found to preserve them between four to six days.

Advantages of the cooler

Farmers can store their produce in the cooler for up to three days so they can harvest more before going to market or wait for buyers to pick them up. With fresher and longer-lasting produce, farmers are able to get good prices for their produce, which enhances their incomes.

The availability of constant water allows the farmer to recycle it and use it in irrigation of the crops or reuse it to cool the store.
It can reduce post-harvest losses by up to 80 per cent depending on the type of vegetable, especially those that perish within hours.

It is a low cost facility easy to construct at farm level by an individual farmer or a cooperative society. It can cost about Shs2m depending on the size.

Dr Apollo Kasharu of Chain Uganda, the implementing agency, says time has come to transfer the technology from the university research to implementation stage.

“We have started with Namulonge Horticulture Farmers Association in Wakiso District with 100 members and the next beneficiaries will be the farmers of Jinja District,” he says.