Pasteurizing Mushrooms in Zimbabwe

In his Grow Further grant application, Dr. Prince Marowa, a senior lecturer at the University of Zimbabwe, reflects fondly on his childhood memories of picking wild mushrooms with friends and family in the Miombo region just north of the capital city of Harare.

“We all loved it,” he wrote. Now as an adult and academic researcher, Marowa is setting out to prove that gathering in the wild is not the only way for people in Zimbabwe and beyond to enjoy the nutritional and food security benefits of mushrooms.

Dr. Marowa came to our attention after submitting his research team’s grant application to Grow Further’s first call for proposals. After a thorough review, his vision for smallholder farm innovation ultimately made the top 20 list of finalists. We are getting closer to announcing our final grant recipients, but we’re not quite there yet. Nevertheless, we found this research plan compelling enough to share with our newsletter’s readers to earn it broader attention. Toward that end, Marowa kindly took our questions to better explain what he and his research partners have in mind.

In short, Marowa and his partners say they aim to develop methods for cultivating and then pasteurizing varieties of mushrooms in a bid to further expand food production at smallholder farms.

Gathering vs. growing

Today, people in Zimbabwe still acquire mushrooms mainly by gathering them, but Marowa is hopeful that he and his partners can overcome the hurdles preventing mushroom farming from taking root in his native country.

“Zimbabwe has the potential to be an ideal location for widespread mushroom cultivation due to its favorable climate and availability of agricultural waste resources,” Marowa explained in an interview. “The climatic conditions in Zimbabwe can support the growth of most artificially cultivated mushroom strains which are cool, medium, and high-temperature strains. However, several factors have hindered the development of this industry and led to a preference for wild mushroom collecting over artificial production.”

For instance, Marowa says many farmers are simply unaware that they can farm mushrooms in quantities large enough to make it worth the effort. They also typically don’t know how to do it; thus, farmers tend to stick with their traditional crops even when told that growing mushrooms is an option for the climate and soil conditions they are dealing with.

“Many farmers in the country are more familiar with traditional agricultural practices such as crop cultivation and livestock rearing,” Marowa explained. “As a result, they may not be aware of the potential profitability and sustainability of mushroom cultivation.”

A better method for preserving mushrooms

Once grown, farmers next need to find a way to preserve this food that tends to spoil rather quickly. Drying is the usual approach. Marowa is now proposing a different method: pasteurization, the process of heat-treating foods such as dairy products to eliminate pathogens or bacteria that cause food to spoil quickly.

“To those who are familiar with artificial mushroom cultivation, lack of effective pasteurization techniques and skills results in contamination,” Marowa noted, “and this normally leads to abandonment of the venture, forcing them to resort to picking wild mushrooms and going back to their traditional agricultural practices.”

In other words, in addition to teaching farmers how to grow mushrooms, Marowa and his team hope to instruct them in proper methods of pasteurization, thereby extending the shelf life of these products and showing Zimbabwe’s farmers a clear path to profitability. In their application, Marowa and his fellow researchers say they will focus on developing best practices for a pasteurization technique known as substrate pasteurization.

“Substrate pasteurization is a crucial process in mushroom production that involves heating the growing medium or substrate to eliminate harmful microorganisms—weed fungi—while preserving beneficial ones,” he said. “This technique is widely used in commercial mushroom cultivation to create a favorable environment for the growth of mushroom mycelium and prevent contamination.” The process involves “steam, hot water immersion, or hot air circulation”.

By “substrate” Marowa is referring to the medium within which mushrooms would be grown at farms or greenhouses. It “can consist of various organic materials such as straw, wood chips, sawdust, or agricultural waste,” he said. “These materials often contain naturally occurring microorganisms, including bacteria, fungi, and molds. While some of these microorganisms may be beneficial for mushroom growth, others can compete with or inhibit the growth of the desired mushroom species.”

“This technique is widely used in commercial mushroom cultivation to create a favorable environment for the growth of mushroom mycelium and prevent contamination”

It’s a delicate balance: applying pasteurization to kill the microorganisms that mushroom farmers don’t want while preserving the ones they do. Marowa says he hopes, through his research, to sort out the most environmentally friendly and sustainable substrate pasteurization methods best suited for smallholder mushroom agriculture. Once that is achieved, he envisions establishing “centers of excellence” to train a new generation of mushroom farmers. As production rises, communities’ reliance on mushroom picking should diminish over time, he says, and a new agricultural market may emerge.

Understanding the present to build a better future

First, Marowa says it’s important to thoroughly investigate where mushroom farming practices currently stand in Zimbabwe, to figure out why these foods are largely failing to entice more farmers to grow them.

“This should include identifying the types of mushrooms that are suitable for cultivation in the region, understanding the existing knowledge and practices among farmers, and assessing the market demand for mushrooms,” he said. After that comes “training programs that cater to farmers with varying levels of experience and knowledge.”

Establishing mushroom farming at a large scale, large enough to accrue real tangible benefits to thousands of farmers and consumers, is a lofty goal. Marowa believes all the pieces are in place to help them succeed: an ideal climate, a competent and effective agricultural extension service in Zimbabwe, and a media infrastructure that can help spread the word and educate farmers on how they can succeed by growing and pasteurizing mushrooms. The key, he told us, is to establish effective programs to disseminate both awareness and knowledge.

“These programs should cover all aspects of mushroom cultivation, including substrate preparation, spawn production, mushroom house construction, disease management, harvesting techniques, and post-harvest handling.”

— Grow Further

Photo credit: Women collecting mushrooms in Zambia. CDK Network, Creative Commons 2.0 Generic (CC BY 2.0).

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