Simple technology to dry your farm produce

A crop scientist explains how the machine operates. PHOTO | GEORGE KATONGOLE

The weather has become extremely erratic, making it harder for farmers to know when to plant, harvest and more importantly, dry their produce as they have done over the years.

It is currently raining heavily in some parts of the country at a time when farmers, in particular those growing maize, should be harvesting their produce.

The unpredictable weather makes the traditional drying of various farm produce under the sun harder.

Luckily, there is a new technology to help you dry your produce for a longer shelf-life.

Refractance window drying
Having transformed a former storage facility at Kabanyolo, a team of food scientists and engineers led by Prof John Muyonga are confident they have an efficient Refractance Window Drying (RWD) technology that can transform dry fruit processing.

The highly adaptive drier, can be used to process fruits such as mango, banana and pineapples, vegetables, as well as commercial production of scrambled egg mix, avocado powder, high carotenoid-containing algae, herbal extracts and human nutrition supplements.

According to the Food and Agriculture Organisation (FAO), food waste remains an elephant in the room for food processors, with about half of crops lost due to poor harvesting and handling techniques.

In Uganda, about 30 per cent of crops are lost every year after harvest, with fruits and grains most affected because of the few food processing centres, according to the Ministry of Agriculture.

Challenged with offering a solution to the substantial losses and improving market access with value-added products, due to the growing demand of nutritious products, the scientists explored options of using the RWD system as an option.

Refractance window drying is a practice that has gained a lot of attention in food processing in recent years, owing to the numerous benefits.

Besides its ability to handle a diverse liquid product, it can be used effectively to transform fruits, vegetables, herbs and other related products into value added powders and concentrates.

There are various methods of drying in Uganda but the most commonly used is solar which is considered to be slower as it takes at least two or three days depending on the weather.

According to Prof Muyonga, this drying method is normally inconsistent on colour and yet it leads to loss of vitamins and flavours.
Novel technology
The Makerere University School of Food Technology, Nutrition & Bio-Engineering (SFTNB) had a watershed moment in 2018 partnering with other universities in the region to develop models of RWD dryers that can be used to produce quality dried products.

This was found effective as RWD systems are simple and relatively inexpensive when compared with freeze drying, which usually needs large installations to be economical.

In RWD systems, thermal energy is transferred from hot water to a film of fruits slices or juice spread thinly on a polyethylene membrane.

The resultant infrared waves cause rapid drying in the material placed on the membrane leading to a short drying period of about 45 minutes to one hour for layers not exceeding 44mm. The use of hot water as the heat transfer medium and at temperatures just below boiling is a design feature that is unique to this drying method.

The RWD method has become attractive for applications in the food industry, especially because the dried products are of high quality and the equipment is relatively inexpensive.

The cost of Refractance Window drying equipment is approximately one third to one half that of a freeze dryer to dry a similar amount of product, while the energy costs to operate RW dryers are less than half of freeze dryers.

The retention of food quality in a drying process rather than mere extension of shelf life has gained prominence because of consumers demand for more health-promoting foods.

Since 2019, the researchers have experimented with dry pineapples, jackfruit, mango and passion fruits.

The scientists have already developed a laboratory scale RWD dryer, a batch dryer which can use biomass and electricity and a continuous dryer powered by electricity.
By using the RWD technology, Prof Muyonga says they are able to make dry slices which can be eaten as healthy snacks. The dried fruit pieces can also be used as ingredients in other foods especially cakes and yoghurt.

“We have also produced powders that can be used in preparing fruit-based drinks or as an ingredient for example, in flavoured yoghurt.”

The researchers have trained more than 20 farmers and agro-processors in the use of the technology and are working towards establishing a platform to facilitate community use of the technology.