Fermentation method transforms unripe fruits into specialty coffees
Normally discarded, green beans from the Arara cultivar were subjected to airless fermentation and produced high-quality beverages in blind tests. Researchers see potential for the product to be valued in domestic and foreign markets
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Luiza Braga appreciates the aroma of Arara coffee beans during drying after anaerobic fermentation. The method improved the quality of immature beans
view moreCredit: Da Semente à Xícara Group/archive
In the selection of specialty coffees, those that score above 80 points in blind tests are free of physical and sensory defects. Greenish-colored beans are known to give the drink an astringent taste, which is described as harsh, pungent, and dry. These beans are therefore discarded, along with broken, black, burnt, pitted, or undersized beans.
However, in a study published in the journal Food and Bioprocess Technology, researchers from the Federal University of Uberlândia (UFU) in Patos de Minas (state of Minas Gerais, Brazil) conducted a series of fermentations with ripe and unripe fruits of the Arara cultivar of Arabica coffee (Coffea arabica). As a result, they obtained beverages comparable to and even superior to those prepared with beans from only ripe fruits, following all the protocols of the Specialty Coffee Association (SCA), an international organization that sets standards for specialty coffees.
In blind cup tests, which evaluate coffee based on its sensory attributes, professional tasters (known as Q-graders) gave beverages containing a percentage of unripe fruit beans scores above 80, which defines specialty coffee.
The researchers achieved these results using self-induced anaerobic fermentation (SIAF), in which the fruits are placed in bioreactors – 200-liter polystyrene barrels that are hermetically sealed – for up to 96 hours after harvesting. No oxygen enters the bioreactors, and carbon dioxide is released through a valve. The microorganisms naturally present in coffee fruits then carry out a series of biochemical processes that result in a distinctive coffee flavor. In some experiments, inoculants – specific microorganisms previously isolated for this purpose – were added to this type of fermentation.
“With this work, we saw that using SIAF at different fermentation times, with temperature and pH control and with or without the addition of inoculum, can not only minimize the deleterious effects of immature beans on the beverage but also make it superior, adding value to the product while still on the farm,” says Luiza Braga, first author of the study, conducted as part of her master’s degree in the Graduate Program in Food Engineering at the Faculty of Chemical Engineering (FEQ-UFU) in Patos de Minas.
The work is part of a project supported by FAPESP through an agreement with the Ministry of Science, Technology, and Innovation (MCTI), in a partnership between UFU and the Federal University of Lavras. Additional funding for the study was provided by the Minas Gerais State Research Support Foundation (FAPEMIG), the Coordination for the Improvement of Higher Education Personnel (CAPES, an agency that belongs to the Ministry of Education), the National Council for Scientific and Technological Development (CNPq), and the Brazilian Innovation Agency (FINEP). The latter two agencies are linked to the MCTI.
“Anaerobic fermentation, carried out immediately after harvesting and before drying, is not a traditional process. However, coffee growers and experts have been seeking knowledge about the process because of the gain in flavor and aroma it brings to the drink, which can then fetch higher prices than those usually found on the market,” says Líbia Diniz Santos, a professor at FEQ-UFU and coordinator of the study.
The authors of the study are members of the research group named Da Semente à Xícara (which translates as “from seed to cup”), created in 2019 to bring together researchers, students, postgraduates, and technicians from FEQ, the Institute of Genetics and Biochemistry, and the faculties of Electrical and Computer Engineering, all on the Patos de Minas campus of UFU. The group even has its own brand of specialty coffee, Porandu, which means “to research” or “to investigate” in Tupi.
Analysis
The Arara cultivar was launched in 2012 by the Procafé Foundation after 15 years of research in search of a disease-resistant coffee adapted to the diverse climatic conditions of Brazil’s Cerrado savanna biome. The drink is valued for its citrus notes and robust body, making it attractive to both the domestic and export markets.
The authors of the study used an artificial intelligence tool developed by the research group and noted that 70% of the fruits used in the experiments, which were harvested at Fazenda Chuá in Patos de Minas, were immature.
Despite using green beans in the beverages tasted by the panelists, the authors emphasize that the other SCA criteria were strictly followed. Thus, broken and small beans were discarded during preparation. Consequently, green beans represented 13% to 30% of the total beverage. “We believe that if there had been 70% green beans in the beverage, even if fermented, this would have been noticeable in the final product,” Santos points out.
A total of 32 treatments were tested, including different fermentation times ranging from 24 to 96 hours with and without temperature control. The combinations also included the presence or absence of inoculum, as well as submerged fermentation with 30% of the bioreactor filled with water or fermentation in a solid state without water.
The group developed an electronic device that monitors the pH and temperature and transmits the data from sensors inside the bioreactor to an external monitor. This eliminates the need to open the barrel and interfere with the experiment in order to collect information.
“When we controlled the external temperature at 27 °C, we observed that the scores were higher, even higher than those of preparations containing only ripe beans. With this, we can demonstrate that anaerobic fermentation, especially in a solid state, adds sensory attributes that elevate the coffee to the special category,” Braga explains.
The group now intends to understand which compound or compounds generated in the fermented green bean provide the sensory attributes that give the coffee its special qualities. Future work will also explore the effect of anaerobic fermentation on other coffee varieties.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
Journal
Food and Bioprocess Technology
Article Title
Transforming Challenges into Quality: The Power of Controlled Fermentation in Immature Arara Coffee Beans
Would you like that coffee with iron?
New microparticles containing iron or iodine could be used to fortify food and beverages, to help fight malnutrition.
Massachusetts Institute of Technology
Around the world, about 2 billion people suffer from iron deficiency, which can lead to anemia, impaired brain development in children, and increased infant mortality.
To combat that problem, MIT researchers have come up with a new way to fortify foods and beverages with iron, using small crystalline particles. These particles, known as metal-organic frameworks, could be sprinkled on food, added to staple foods such as bread, or incorporated into drinks like coffee and tea.
“We’re creating a solution that can be seamlessly added to staple foods across different regions,” says Ana Jaklenec, a principal investigator at MIT’s Koch Institute for Integrative Cancer Research. “What’s considered a staple in Senegal isn’t the same as in India or the U.S., so our goal was to develop something that doesn’t react with the food itself. That way, we don’t have to reformulate for every context — it can be incorporated into a wide range of foods and beverages without compromise.”
The particles designed in this study can also carry iodine, another critical nutrient. The particles could also be adapted to carry important minerals such as zinc, calcium, or magnesium.
“We are very excited about this new approach and what we believe is a novel application of metal-organic frameworks to potentially advance nutrition, particularly in the developing world,” says Robert Langer, the David H. Koch Institute Professor at MIT and a member of the Koch Institute.
Jaklenec and Langer are the senior authors of the study, which will appear in the journal Matter. MIT postdoc Xin Yang and Linzixuan (Rhoda) Zhang PhD ’24 are the lead authors of the paper.
Iron stabilization
Food fortification can be a successful way to combat nutrient deficiencies, but this approach is often challenging because many nutrients are fragile and break down during storage or cooking. When iron is added to foods, it can react with other molecules in the food, giving the food a metallic taste.
In previous work, Jaklenec’s lab has shown that encapsulating nutrients in polymers can protect them from breaking down or reacting with other molecules. In a small clinical trial, the researchers found that women who ate bread fortified with encapsulated iron were able to absorb the iron from the food.
However, one drawback to this approach is that the polymer adds a lot of bulk to the material, limiting the amount of iron or other nutrients that end up in the food.
“Encapsulating iron in polymers significantly improves its stability and reactivity, making it easier to add to food,” Jaklenec says. “But to be effective, it requires a substantial amount of polymer. That limits how much iron you can deliver in a typical serving, making it difficult to meet daily nutritional targets through fortified foods alone.”
To overcome that challenge, Yang came up with a new idea: Instead of encapsulating iron in a polymer, they could use iron itself as a building block for a crystalline particle known as a metal-organic framework, or MOF (pronounced “moff”).
MOFs consist of metal atoms joined by organic molecules called ligands to create a rigid, cage-like structure. Depending on the combination of metals and ligands chosen, they can be used for a wide variety of applications.
“We thought maybe we could synthesize a metal-organic framework with food-grade ligands and food-grade micronutrients,” Yang says. “Metal-organic frameworks have very high porosity, so they can load a lot of cargo. That’s why we thought we could leverage this platform to make a new metal-organic framework that could be used in the food industry.”
In this case, the researchers designed a MOF consisting of iron bound to a ligand called fumaric acid, which is often used as a food additive to enhance flavor or help preserve food.
This structure prevents iron from reacting with polyphenols — compounds commonly found in foods such as whole grains and nuts, as well as coffee and tea. When iron does react with those compounds, it forms a metal polyphenol complex that cannot be absorbed by the body.
The MOFs’ structure also allows them to remain stable until they reach an acidic environment, such as the stomach, where they break down and release their iron payload.
Double-fortified salts
The researchers also decided to include iodine in their MOF particle, which they call NuMOF. Iodized salt has been very successful at preventing iodine deficiency, and many efforts are now underway to create “double-fortified salts” that would also contain iron.
Delivering these nutrients together has proven difficult because iron and iodine can react with each other, making each one less likely to be absorbed by the body. In this study, the MIT team showed that once they formed their iron-containing MOF particles, they could load them with iodine, in a way that the iron and iodine do not react with each other.
In tests of the particles’ stability, the researchers found that the NuMOFs could withstand long-term storage, high heat and humidity, and boiling water.
Throughout these tests, the particles maintained their structure. When the researchers then fed the particles to mice, they found that both iron and iodine became available in the bloodstream within several hours of the NuMOF consumption.
The researchers are now working on launching a company that is developing coffee and other beverages fortified with iron and iodine. They also hope to continue working toward a double-fortified salt that could be consumed on its own or incorporated into staple food products.
The research was partially supported by J-WAFS Fellowships for Water and Food Solutions.
Other authors of the paper include Fangzheng Chen, Wenhao Gao, Zhiling Zheng, Tian Wang, Erika Yan Wang, Behnaz Eshaghi, and Sydney MacDonald.
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Written by Anne Trafton, MIT News
Journal
Matter
Article Title
Ferrous Nutritional Metal Organic Framework (NuMOF) as Food Fortificant
Article Publication Date
13-Aug-2025
