Coffee Roasting Finally Gets an Overdue Green Makeover

Antonio Durbe and Daniele Tummei, two engineers from Rome, watch on as fresh coffee beans inside a steel basket begin to turn a deep nutty brown. They are just outside the city in a small clearing bordered by low trees. A couple of meters away, a wall of mirrors angle sunlight directly onto the rotating beans. After about 20 minutes on this hot day, the beans are fully toasted.

This isn’t how coffee beans are traditionally roasted. Normally, currents of hot combustion gases are applied to toast batches of beans rotating in a drum. This generates a stream of greenhouse gas emissions that end up in the atmosphere and contribute to climate change. A 2017 study by the Journal of Sustainable Energy & Environment found that roasting one kilogram of green beans produced 1.67 kg of carbon dioxide. Europe is home to the largest coffee roasting industries and Germany, which is the largest coffee roaster, produced 572 thousand tonnes of roasted coffee in 2019. That equates to roughly 1 million tonnes of carbon dioxide. “Now, we are all very conscious that carbon dioxide emissions are contributing to the warming of our planet, and roasting coffee is a big emitter,” Durbe told The Daily Beast. “There is little innovation in this sector. Coffee is roasted in the same way as hundreds of years ago.”

Durbe and Tummei’s new roasting plant is a bid to change all of that. Called Purosole, it uses a collection of mirrors to focus the rays of the sun onto a rotating basket of beans. This produces intense heat that is sufficient for the toasting process. The mirrors automatically follow the movement of the sun (“like sunflowers,” says Durbe), and their motors are also powered by small photovoltaic cells. Powered solely by the sun, Purosole can reach 250 degrees Celsius and toast 50 kg of beans in an hour. The whole roasting process produces, in the words of Durbe, “not even a gram of carbon dioxide.”

Durbe and Tummei already have clients interested in buying their plant, both in Italy and in countries like France and the U.S. Though they do not see their system as a viable technology for large-scale, industrial coffee roasting, they believe it could be a brilliant solution for small to medium-sized coffee producers or businesses.

They may have a point. The last decade has seen the rise of so-called “micro roasters.” These companies roast small batches of beans and usually supply local cafés and businesses, or their own outlet. With their particular focus on artisanal and select brews, Purosole’s ethos is well matched.

And the requirements are fairly simple: a large plot of land and a sunny climate. Many requests have come from the southern Italian region of Calabria, for example, where there is plenty of land and sunny days. In July, for example, there is an average of 12.6 hours of sunshine a day.

Aside from being green, Durbe said the Purosole plant also produces a superior flavor of bean. “When you compare beans toasted with the traditional gas burners with our beans, the difference is clear,” he said. “The beans remain more crunchy, the toasting is much more uniform and the taste and scent are much better.”

Traditional plants immerse the beans in hot air, and so the exterior of the bean is exposed to temperatures of up to 600 degrees Celsius. With Purosole, instead, the temperature rises slowly to bring the beans gradually up to 250 degrees Celsius. Beans crack at these temperatures—a sign that they are ready. The high levels of fat in the coffee bean, which degenerate when in contact with extremely high temperatures, stay undamaged.

Despite these advantages, Durbe points out the obvious that the plant is completely dependent on the sun. “One passing cloud is enough to stop everything!” he said. As a result, it is a system for those interested in improving the quality of their coffee in an environmentally friendly way rather than those looking to produce a large and consistent supply.

A steady stream of heat is essential for coffee production. Maria Franco, a researcher at the Università degli Studi in Italy who is currently studying the carbon footprint of coffee in Peru, told The Daily Beast that, “For luxury products such as coffee we are always looking for consistency and bean quality. Sometimes using solar energy through a solar concentrator cannot guarantee consistency of the energy and consistency of the roasting process.” In order to develop a consistent and unique coffee blend, “you need to guarantee that amount of heat infinite times,” she said.

While Purosole is proving successful in significantly decreasing the emissions of coffee roasting, there are still many other stages of the whole coffee production process that contribute to its carbon footprint. While roasting accounts for up to 15 percent of the cradle-to-grave carbon footprint of coffee, the farming and processing of the beans are very emissions-heavy. A study carried out by the Natural Resources Institute Finland (LUKE) found that these two stages make up 68 percent of coffee’s climate impact. University of Tuscia food scientist Maruo Moresi has also found that the preparation (brewing) of coffee and the post-consumption phases of dishwashing and recycling account for 30 percent of coffee’s carbon footprint.

Still, while the Purosole system may not have an outsized impact on making coffee production more green, Durbe believes it opens the doors for a larger interest in harnessing the power of the sun for various applications—some of which he and his partners are already pursuing. “We are currently building a cooking system for a beach kiosk using the same methods of moving mirrors,” he said. The ability of the Purosole system to move its mirrors autonomously is especially novel, and Durbe thinks it is possible to use this design to guarantee a particularly even, consistent and rapid way of cooking. “In 20 minutes, we cooked a two-kilogram chicken,” he said.

Additionally, Franco sees potential for the Purosole system to bring opportunities to rural areas around the world. “There are still many places worldwide with no power supply,” she said. “To activate the economy and to generate energy in rural areas, Purosole could be successful.” A similar project is underway in rural Perù where there is little access to electricity. Here, said Franco, small coffee farmers are encouraged to toast their harvested green beans in the field with a solar powered roasting plant developed by the company Café Compadre. This is bringing vital income to underpaid workers who often have to sell their green beans at a loss.

Franco also agrees with Durbe and Tommei that diversifying their products could make them appropriate for boosting various agricultural practices, not just coffee production. “In Africa, I am aware that solar concentrators are being used to process fruits and cocoa,” she said.

For Durbe, Purosole is just the beginning of a variety of systems that can produce light or heat in an eco-friendly way. “These are the first steps to harnessing a resource which is permanently there,” he said.