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

Antonio Durbe and Daniele Tummei, two engineers from Rome, watch as the fresh beans inside a steel basket begin to turn a deep brown. They were just outside the city in a small clearing surrounded by low trees. A few meters away, a wall of mirrors beamed sunlight directly onto the spinning beans. After about 20 minutes on this hot day, the beans were fully baked.

This is not the traditional way of roasting coffee beans. Typically, a hot gas stream is applied to toast batches of beans rotated in drums. This creates an eventual stream of greenhouse gas emissions in the atmosphere and contributes to climate change. A 2017 study by Sustainable Energy & Environment Magazine found that roasting one kilogram of green beans produces 1.67 kilograms of carbon dioxide. Europe is home to the largest coffee roasting industries and Germany, the largest coffee roasting country, produced 572 thousand tons of roasted coffee in 2019. This equates to about 1 million tons of carbon dioxide. Durbe told The Daily Beast: “We are all very aware now that carbon dioxide emissions are contributing to the warming of our planet, and coffee roasting is a big waste. “There is very little innovation in this area. Coffee is roasted in the same way it was hundreds of years ago.”

Durbe and Tummei’s new roastery is an attempt to change all that. Called Purosole, it uses a set of mirrors to focus the sun’s rays onto a rotating basket of beans. This creates a high enough temperature for the baking process. The mirrors automatically follow the movement of the sun (“like a sunflower,” says Durbe) and their motors are also powered by small photovoltaic cells. Powered only by the sun, Purosole can reach a temperature of 250 degrees Celsius and bake 50 kg of beans in an hour. In the words of Durbe, the entire roasting process produces “less than a gram of carbon dioxide.”

Purosole’s founders are enjoying a cup of coffee in front of their mirrored roasting system.

Polite Purosole

Durbe and Tummei already have customers interested in buying their plants, both in Italy and in countries like France and the US. solutions for small and medium coffee production or business establishments.

They may have a point. The past decade has seen the rise of so-called “micro-roasters”. These companies roast small batches of beans and often supply them to local cafes and businesses, or to their own shops. With a particular focus on craft and select beers, the Purosole ethos fits perfectly.

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

In addition to the green color, Durbe says the Purosole plant also produces the delicious flavor of the beans. “When you compare traditional gas-fired baked beans with ours, the difference is stark,” he said. “The beans are still crispier, baked more evenly, and much better in flavor and aroma.”


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

Polite Purosole

Traditional mills soak the beans in hot air, and so the outside of the beans is exposed to temperatures of up to 600 degrees Celsius. Instead, with Purosole, the temperature is increased slowly to bring the beans out gradually. up to 250 degrees Celsius. Beans crack at this temperature – a sign that they are ready. The high fat content in coffee beans, which are degraded when exposed to extreme heat, remains unadulterated.

Despite these advantages, Durbe points out that the plant is completely dependent on the sun. “A passing cloud is enough to stop everything!” he say. It is therefore a system for those who are more interested in enhancing the quality of their coffee in an eco-friendly way than those who want to produce a large and consistent supply.

A steady 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 like coffee, We are always looking for consistency and grain quality. Sometimes using solar energy through a solar concentrator cannot guarantee energy consistency and roasting consistency. ” To develop a consistent and unique blend, “you need to make sure that heat goes on indefinitely,” she says.

While Purosole is proving successful in significantly reducing emissions from coffee roasting, there are still many other stages of the entire coffee production process that contribute to its carbon footprint. While roasting accounts for 15% of coffee’s end-to-end carbon emissions, the farming and processing of coffee beans is very emissions-heavy. A study conducted by the Finnish Institute of Natural Resources (LUKE) found that these two stages account for 68% of coffee’s climate impact. Food scientist Maruo Moresi of the University of Tuscia has also found that coffee preparation (brewing) and the post-washing and recycling stages account for 30% of coffee’s carbon footprint.


Beans roasted through sunlight are collected.

Polite Purosole

However, while the Purosole system may not have too much of an impact on the production of greener coffee, Durbe believes it opens the door to greater interest in harnessing the power of the sun. Various applications — some of which he and his partners are pursuing. “We are currently building a cooking system for a beach kiosk using mirror motion methods,” he said. The Purosole system’s ability to automatically move the mirror is particularly novel, and Durbe thinks this design could be used to ensure exceptionally uniform, consistent and quick cooking. “In 20 minutes, we cooked a two-kilogram chicken,” he said.

In addition, Franco sees the potential of the Purosole system to bring opportunities to rural areas around the world. “There are still many places around the world without electricity,” she said. “To activate the economy and generate energy in rural areas, Purosole can be successful.” A similar project is underway in rural Perù, where there is little access to electricity. Here, says Franco, small coffee farmers are encouraged to roast their harvested beans in the field using a solar-powered roaster developed by Café Compadre. This is providing vital income for low-paid workers, who often have to sell their chickpeas at a loss.

Franco also agrees with Durbe and Tommei that diversifying their products could make them suitable for promoting different agricultural activities, not just coffee production. “In Africa, I know that solar concentrators are being used to process fruit and cocoa,” she said.

For Durbe, Purosole is just the beginning of a series of systems that can generate light or heat in an eco-friendly way. “These are the first steps to exploiting a permanent resource there,” he said. New coffee roasting system Purosole roasts beans with the sun to combat the coffee’s carbon footprint


Hung is a Interreviewed U.S. News Reporter based in London. His focus is on U.S. politics and the environment. He has covered climate change extensively, as well as healthcare and crime. Hung joined Interreviewed in 2023 from the Daily Express and previously worked for Chemist and Druggist and the Jewish Chronicle. He is a graduate of Cambridge University. Languages: English. You can get in touch with me by emailing:

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