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Ugandan student researches best drying technique for quality peanuts

By Alex Merritt

University of Georgia, Peanut & Mycotoxin Innovation Lab

John Yawe took a big step moving from his home country of Uganda to pursue a master’s degree in Zambia. With more than 2000 kilometers separating the two countries’ capitals, the differences in culture and language would have deterred many people.

But for Yawe, who graduated late last year from the University of Zambia with a MSc. in Agricultural Engineering, a master’s degree meant more than expanding his horizons or getting a better job. It meant that he could advocate for smallholder farmers, who produce 80% of the food grown in Uganda.

“Getting my master’s would put me in position to advocate and participate in developing a comprehensive food production policy in Uganda,” said Yawe. “The Agricultural Engineering master’s program would enhance my knowledge in research of post-harvest handling and processing at the same time broaden my capacity to develop easily adaptable, accessible, affordable technologies for Ugandan farmers.”


Ugandan agricultural engineer John Yawe (seen here in Lilongwe, Malawi) completed a master's degree from the University of Zambia, where he researched the most effective technique for drying groundnuts. Proper drying and storage are key to discouraging aflatoxin contamination. (Photo by Allison Floyd)

Proper post-harvest handling and processing of crops is key to the economic security of smallholder farmers. In Uganda, improper post-harvest handling means around 32% of food is wasted, much of it due to mold. Some naturally occurring fungi that grow on improperly stored crops can produce aflatoxin, a contaminant that has been linked to liver cancer, as well as stunting in children.

Peanuts – or groundnuts as they are known in Africa – are susceptible to aflatoxin contamination, as is maize, which is also a staple in much of sub-Saharan Africa. In Zambia, groundnuts are the second-most grown crop after maize and are valued for their taste and versatility, as well as their high protein and oil content.

“Groundnuts have a wide range of uses in the daily life of African peasant farmers,” Yawe said. “Despite their unique importance, production and utilization of groundnuts in the smallholder setting is hampered by, among others, infection by fungi and subsequent aflatoxin contamination.”


With support from the Peanut & Mycotoxin Innovation Lab, Yawe researched the efficacy of commonly used drying and storage systems for both in-shell and raw kernel groundnuts. Proper drying and storage of groundnuts translates into lowered aflatoxin contamination further along the value chain.

“Although there are several management strategies that may reduce aflatoxin contamination of groundnuts, drying is considered a key post-harvest operation in the intervention as all activities along the value chain depend on it,” Yawe said.


Yawe-farmer-interviewsJohn Yawe listens as a farmer explains how she dries groundnuts. To complete a master's degree in agricultural engineering from the University of Zambia, Yawe studied the most effective methods of drying peanuts for storage.

He began by surveying 101 smallholder farmers and six focus groups in the Chongwe District of Zambia to determine farmers’ post-harvest attitudes, knowledge, and practices.

The survey showed that 45% of farmers dry groundnuts on the bare ground, and 78% store their dried groundnuts in polypropylene sacks on raised platforms.

Only 17% of the farmers were aware of aflatoxin and how it can harm health. With limited capital, aflatoxin awareness, and available technology, none of the farmers used recommended practices (such as drying on a tarp) to decrease post-harvest loss.

Yawe then experimented with the most common drying methods – papyrus mats, black polythene, wooden drying racks, corrugated iron sheets, compacted ground, and concrete slabs – with groundnuts stacked into layers 1-4 cm deep. As expected, results from the experiments indicated that drying rates increased as layer depth increased. There was no difference in the moisture content of in-shell and raw kernel groundnuts after the drying was completed.


Yawe-drying-tablesUgandan ag engineer John Yawe tested different drying methods for peanuts and at different depths to see what works best.

Of the drying methods he tested, Yawe found that concrete slabs and papyrus mats with groundnuts stacked approximately 4 cm high were the most effective at drying groundnuts and reducing aflatoxin contamination, while the least effective was black polythene with groundnuts stacked approximately 1 cm high. During the experimental time frame, none of the methods brought down the moisture content to the less than 10% moisture content level considered safe for groundnut storage.


“Farmers used poor stripping, drying and storage methods conducive for fungi growth, hence high levels of aflatoxins,” Yawe said. To address these problems, it would be important to develop technologies which are suited for local conditions.

Drawing on what he’s learned from his master’s research, Yawe would make a few adjustments if he were to do it again.

“I would increase the size of the drying areas, as well as the range of depths to 6 cm. I would carry out the experiment on-farm in different agro-ecological zones, and I would develop mathematic models for layer characteristics,” Yawe said.

Yawe’s experience has taught him a lot about what it takes to achieve useful findings.

“I learned that for one to come up with meaningful research results that can impact the community, understanding the theory of change is important. Being a researcher requires having wide knowledge on the topic of research, as well as social and management skills. A researcher also needs a competent and hardworking team to come up with credible data,” Yawe said.

His research left him with more questions about post-harvest drying and storage.

“Before the drying depth and surfaces are promoted, further experiments should be carried out on other varieties of groundnuts,” he said.

With any luck, in the future Yawe will be able to answer questions like this himself.

“Presented with an opportunity, I intend to enhance my capacity to investigate similar challenges through a study or work opportunity anywhere in the world,” he says. Yawe is searching for scholarships in the hopes of pursing a Ph.D.

-Published April 30, 2017