New Purosole coffee roasting system roasts beans in the sun to combat coffee’s carbon footprint

Antonio Durbe and Daniele Tummei, two engineers from Rome, watch fresh coffee beans inside a steel basket begin to take on a deep nutty color. They are just outside of town in a small clearing lined with low trees. A few meters away, a wall of mirrors directs sunlight directly onto the spinning grains. After about 20 minutes on this hot day, the beans are fully toasted.

This is not how coffee beans are traditionally roasted. Normally, streams of hot combustion gases are applied to roast 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 Journal of Sustainable Energy and the 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 572,000 tons of roasted coffee in 2019. This equates to around 1 million tons of carbon dioxide. “Now we are all very aware that carbon dioxide emissions are contributing to the warming of our planet, and coffee roasting is a big emitter,” Durbe told The Daily Beast. “There is little innovation in this sector. Coffee is roasted the same way it was hundreds of years ago.

Durbe and Tummei’s new roasting plant is an attempt to change all that. Called Purosole, it uses a collection of mirrors to focus the sun’s rays onto a rotating basket of beans. This produces intense heat sufficient for the grilling 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 only by the sun, Purosole can reach 250 degrees Celsius and roast 50 kg of beans in one hour. The entire roasting process produces, in Durbe’s words, “not even a gram of carbon dioxide”.

The founders of Purosole enjoying a cup of coffee in front of their mirror roasting system.

Courtesy of Purosole

Durbe and Tummei already have customers interested in buying their plant, both in Italy and in countries like France and the United States. Although they don’t see their system as a viable technology for large-scale industrial roasting, they think it could be a brilliant solution for small and medium-sized coffee growers or businesses.

They may be right. The last decade has seen the rise of so-called “micro-roasters”. These companies roast small batches of beans and usually supply local cafes and businesses, or their own outlet. With their particular emphasis on craft and selected beers, Purosole’s philosophy is well matched.

And the requirements are quite simple: a large plot and a sunny climate. Many requests came from the region of southern Italy, Calabria, for example, where there is a lot of land and sunny days. In July, for example, there are an average of 12.6 hours of sunshine per day.

In addition to being green, Durbe said the Purosole plant also produces a superior bean flavor. “When you compare beans roasted with traditional gas burners with our beans, the difference is clear,” he said. “The beans stay crisper, the roast is much more even, and the taste and smell are much better.”

These mirrors direct sunlight to a focal point where the coffee beans are naturally roasted.

Courtesy of Purosole

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

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

A constant flow 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 the consistency and quality of grains. Sometimes the use of solar energy through a solar concentrator cannot guarantee the consistency of energy and the consistency of the roasting process. In order to develop a consistent, unique coffee blend, “you have to guarantee that amount of heat endlessly,” she said.

Although Purosole succeeds in significantly reducing emissions from coffee roasting, there are still many other steps in the entire coffee production process that contribute to its carbon footprint. While roasting accounts for up to 15% of coffee’s cradle-to-grave carbon footprint, growing and processing the beans is highly polluting. A study by the Natural Resources Institute Finland (LUKE) found that these two steps account for 68% of coffee’s climate impact. University of Tuscia food scientist Maruo Moresi also found that the preparation (brewing) of coffee and the post-consumer phases of dishwashing and recycling account for 30% of coffee’s carbon footprint.

Sun-roasted beans are collected.

Courtesy of Purosole

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

Additionally, Franco sees the potential of the Purosole system to bring opportunities to rural areas around the world. “There are still many places in the world without power,” she said. “To activate the economy and produce energy in rural areas, Purosole could succeed.” A similar project is underway in rural Peru where access to electricity is limited. Here, Franco said, small-scale coffee farmers are encouraged to roast their field-harvested green beans with a solar-powered roasting plant developed by the Café Compadre company. This provides vital income for 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 suitable for boosting various agricultural practices, not just coffee production. “In Africa, I know solar concentrators are used to process fruit and cocoa,” she said.

For Durbe, Purosole is just the start of a variety of systems that can produce light or heat in an environmentally friendly way. “These are the first steps to exploiting a resource that is there all the time,” he said.