Scientists test protein upcycling by using maize (corn) leftovers to grow mushrooms, then using the more nutritious by-product to feed earthworms, which are a viable alternative protein source for humans and nonhuman animals.
By Nigel Chimbetete
With global protein demands rising and conventional agriculture reaching ecological limits, researchers are turning to unconventional yet promising solutions. A novel bioconversion pathway links maize stover, oyster mushroom cultivation, and earthworm farming to create a sustainable strategy to upcycle agricultural waste into high-quality edible protein. This innovation has implications for food security in resource-limited regions.
Falling protein production and booming mushroom farms
Traditional protein production systems are gradually falling out of favor and for good reasons. Concerns abound due to greenhouse gas emissions, land scarcity, dwindling water resources, and the alarming loss of biodiversity driven by the conversion of natural wildlife habitats into agricultural land. These issues have cast a shadow over conventional methods. Some regions are burdened by soaring population growth, limited arable land, and fragile economies. As a result, they struggle to meet the nutritional demand for human edible protein, leaving millions vulnerable to malnourishment.
The Western “mushroom boom” was inspired by the global “functional foods” trend dating back to the early 2000s. It saw a surge in mushroom usage, primarily due to biotechnology advances. Expanded mushroom applications include health supplements, plant-based diets, adaptogens, and coffee substitutes. Despite its growing success, the mushroom industry faces the continued increase of waste material, especially spent mushroom substrate. In large amounts, these waste materials could threaten the environment and public health due to nutrient leaching.
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Mushroom farmers and the waste stream
On March 19, 2024, Doug Bierend published an article in Civil Eats where he described walking up to Collar City Mushrooms. Their small-scale mushroom production based in Troy, New York, generates about 1,000 pounds of mushrooms per week. Doug writes, “Out back, baking in the winter sun between a shed and a yellow Volkswagen bus, sits a waist-high heap of what looks like dozens of giant Frosted Mini-Wheats, each roughly the size of a cinder block.”
What Doug describes is blocks of spent mushroom substrate. These lumps are the leftover material after mushrooms have grown and harvested. Typically, these mushroom substrates comprise a carbon source such as cellulose, nitrogen, soybean meal or wheat bran, minerals, and additional growth-promoting supplements with the percent composition tailored to the mushroom farmed.
“Right now, we have people picking it up almost as a favor for us because otherwise, what are we doing with it?” said Collar City Mushroom co-founder Avery Stempel.
“If you’re gonna [farm mushrooms], awesome, but account for this waste stream you’re producing and how you’re gonna get it off your property.” That’s the advice of Amanda Janney, founder of KM Mushrooms in California.
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Transforming mushroom waste for protein upcycling
Fast forward to the present day: A team of researchers from Wageningen University in the Netherlands and research partners in Germany have discovered a method that could transform this spent mushroom substrate into protein. Their work focuses on areas, especially sub-Saharan Africa, where protein consumption per capita remains critically low. The team saw the untapped potential and became the first researchers investigating the upcycling of protein from maize stover to mushroom substrate and, finally, to protein biomass. And where does the protein come from exactly? The answer has been wriggling under our toes the whole time—earthworms!
What is protein upcycling, and what on earth do worms have to do with it?
Upcycling fuses two global initiatives (sustainability and recycling) by turning waste products into new and higher-value-added products. This study explored an integrated bioconversion approach using three regionally abundant and underexploited resources: maize stover (post-harvest leaves and stalks of maize/corn), earthworms (E. fetida and E. eugeniae), and oyster mushroom substrate. This is the first study to compare earthworm biomass and protein quality when fed maize stover.
Maize is the most popular carbohydrate-dense food farmed in the sub-Saharan region. Maize stover is the leftover material that is recycled as soil enrichment and livestock feed. It can also be used as an oyster mushroom substrate.
Rich in essential amino acids, fatty acids, nutrients, and vitamins, earthworms have wriggled their way onto culinary plates across the globe, from New Zealand and China to Japan and Venezuela. To ensure their safety for both human and animal consumption, earthworms should be classified as “farmed animals” and raised on strictly regulated, pathogen-free substrates. In the EU and USA, for example, the regulatory bodies responsible for overseeing food production standards require a testing process of both the feed substrate and the final earthworm product. This thorough testing instills confidence in the safety of earthworms as a food source.
Nitty-gritty of earthworm farming
The process of converting earthworms into human food or animal feed follows a step-by-step approach. Once the substrate has been designated as safe, it is introduced to the earthworms for feeding. Once the earthworms reach the cultivation stage in their growth phase, they are harvested and undergo a thorough cleaning process. This is followed by a drying process, typically through oven drying or freeze drying. The dried product can then be stored as whole earthworms, often sold commercially as “jerky,” or milled into a fine meal. This meal can serve as a base ingredient for animal feed or be incorporated into human food products, such as protein bars, pasta, or baked goods.
Although traditionally used as fishing bait or soil enhancers, the protein-rich composition of earthworms, ranging from 51 percent to 71 percent on a dry matter basis, makes them a strong contender in the search for alternative protein for human consumption.
Scraps to surplus: Maximizing protein yields
In this study, for a total of 37 days, the two species of earthworms were fed either maize stover directly or spent oyster mushroom substrate made from maize stover. To determine the protein yields, the researchers tracked the growth of the nitrogen (a key chemical component in protein composition) content in the oyster mushrooms and earthworms. Since mushrooms require spawn (nitrogen-containing starter) to initiate growth, they adjusted the numbers to make a fair comparison. They scaled the numbers based on maize stover left on a typical Ugandan farm.
Finally, they tracked how efficiently nitrogen in the original waste product (maize stover) was converted into consumable protein-rich human food made of earthworms. The results showed up to 29kg of crude protein could be harnessed from consecutive farming of oyster mushrooms and earthworms compared to oyster mushroom farming alone. Moreover, they measured a 238 percent increase in protein yields compared to direct feeding of maize stover to earthworms.
Not only did the yields in this study show promising results, but the composition quality showed that they contained lysine and tryptophan, two essential amino acids that are commonly deficient in maize-based diets.
The limitations, drawbacks, and potential of protein upcycling from mushrooms and earthworms
Some drawbacks worth mentioning are the economic and logistical challenges of transportation and storage of maize stover. In addition, competing factors based on the other streams of maize stover usage, such as soil amendment and livestock feed, could impact the availability of mushroom substrate and, by domino effect, minimize the earthworm feed.
In contrast, the positives outweigh the negatives regarding protein upcycling. Cultivating earthworms fed by mushroom waste could yield 115 percent more protein than just mushroom farming alone. To further illustrate how this can affect your day-to-day livelihood, imagine that you are a farmer with limited farmland, less than 15 percent of an acre. If you planted maize, harvested it, and used the maize stover to grow mushrooms, you could use the leftover mushroom substrate for farming earthworms for human consumption. This source could meet up to 8.7 percent of your daily protein requirement. If you used that maize stover directly as earthworm feed, this would only fulfill 2.6 percent of your daily protein requirement. Therefore, this illustrates the multiplying effect of protein yields based on efficient and enhanced upcycling methods on every stage of waste product utilization.
Future outlook for earthworm farming
The economic benefit of combining oyster farming and earthworm farming could see the rise of small-scale farmers and producers. In Kampala, the average annual profit for an oyster mushroom farmer can range from $9.5k to $170k. Earthworm farmers in the same regions may experience over 200 percent ROI within 5 years.
This approach fits into the global goal of a more sustainable future. It has great potential to synergistically transform agricultural waste into alternative edible nutrition sources in regions facing malnourishment. Urgent solutions are needed not only to relieve current deficiencies but also to create sustainable pathways for long-term nutritional security in such regions.
This study was published in the peer-reviewed Journal of Environmental Management (JEM).
References
Bierend, D. (2024, March 19). Managing “brown gold”: The challenges—and opportunities—of spent substrate. Civil Eats. https://civileats.com/2024/03/19/managing-brown-gold-the-challenges-and-opportunities-of-spent-substrate/
Sonntag, E., Vidal, A., Aulrich, K., Grimm, D., Rahmann, G., van Groenigen, J. W., van Zanten, H., & Parodi, A. (2025). Earthworm farming for enhanced protein upcycling from spent mushroom substrate. Journal of Environmental Management, 385, 125325. https://doi.org/10.1016/j.jenvman.2025.125325
Tedesco, D. E. A., Conti, C., Lovarelli, D., Biazzi, E., & Bacenetti, J. (2019). Bioconversion of fruit and vegetable waste into earthworms as a new protein source: The environmental impact of earthworm meal production. Science of the Total Environment, 683, 690–698. https://doi.org/10.1016/j.scitotenv.2019.05.226
Featured image “20060131 earthworm dives” by schizoform on Flickr, licensed under CC by 2.0.
About the Author
Nigel Chimbetete has a PhD in Food Science, specializing in Nutritional Biochemistry and Food Product Development. He is passionate about all topics surrounding food biochemistry and food sustainability. Outside of the lab, Nigel enjoys spending time with his family, traveling, and playing five-a-side soccer with his local community. Connect with him through @ChimbesHealth on X and on Instagram @dr.chimbeshealth.
