A Charcoal Cooler Increased the Shelf Life of My Vegetables from 4 Days to 20 Days

Many farmers who deal with fresh produce face post-harvest losses and reduced profits due to poor or lack of proper storage facilities for their produce before they reach the market or before they are sold. The impact might be even worse now that the Corona virus pandemic has disrupted the supply chain for a lot of farmers.

‘Necessity is for sure the mother of invention.’ Farmers need to come up with innovative ways of preserving their perishable farm produce to reduce losses.

Charcoal Cooler

With locally available materials such as charcoal, wire mesh, water pipes and a water tank, farmers can make an innovative, low-cost refrigerator to store their perishable produce such as fruits and vegetables.

It is a storage facility that is easy to construct at farm level by an individual farmer or by a cooperative society.

According to a farmer in Kirinyaga County, the charcoal cooler can keep fruits and vegetables fresh for more than a week. “My French beans’ shelf life has increased from 4 days to 20 days and kales’ from 3 days to 7 days, since I started storing them in a charcoal cooler. They stay fresh for all these days and do not shrink in weight,” said Monica.

The design

A charcoal cooler is basically a room with charcoal walls. The walls are constructed from a wooden frame covered with wire mesh separated by about 10 cm with the interior being filled with charcoal. The charcoal walls are on all four sides, filled up to the top 15 to 20 cm below the roof, with this space being left open so as to allow air circulation.

A network of perforated water pipes going round the top of the charcoal walls are fed with water from an overhead tank, where the water continuously drips, similar to a drip irrigation system, all the way to the bottom of the charcoal walls. Excess water dripping from the charcoal can be collected for reuse.

The roof should be made preferably with thatch or any other material that provides a cool shade.

The floor can simply be bare ground that is compacted, however a floor made of cement or bricks is more durable. Use of wooden pallets on the floor is advisable to keep the produce off the ground, reducing the likelihood of infection by soil borne diseases and molds in general.

How the cooler works

The cooler works based on the principle of a porous structure to which water is added and as air flows across the “wet wall” the air temperature is decreased due to the loss of heat through evaporation of water.

Charcoal is an ideal material for this kind of refrigerator because it has a very porous structure that can absorb and store water. As the warm, dry air flows through the moist charcoal, water evaporates and as a result, cools the air inside the room. Charcoal is also a bad conductor of heat, hence conventional entry of heat is limited in this case.

Temperatures inside the room can be lowered to as low as five degrees Celsius, depending on the relative humidity of the ambient air. Charcoal coolers work best in regions where the moisture content in the air is below 30 percent.

The lower temperatures in the cooler reduces the spoilage rate of fresh farm produce, allowing for more time to sell.

Site selection

Charcoal coolers rely on air movement in order to be effective, thus coolers should not be placed in locations which receive little or no wind. Ample supply of water is required to render the cooler operational and so the site should have a good source of water close by.