Roasting coffee with the rays of the sun

Engineers have created an environmentally friendly way to roast coffee beans without electricity or gas.

The created system is a sunlight coffee roaster, that needs a piece of land about the size of half a tennis court and sunny weather to roast up to 50 kilograms of coffee an hour.

Sunrays are concentrated by a set of mirrors on a coffee roaster and even the few electrical parts are powered by a small solar panel. Sensors controlled by a computer allow the mirrors to follow the sun throughout the day and focus its light on a rotating steel basket that contains the fresh coffee beans. The basket reaches peak temperatures of about 240-250º C, depending on the sun's brightness, and can roast the beans in 20 min.

The process isn't only environmentally friendly and economically convenient. It also better preserves the coffee's aroma, giving it a richer flavour. Unlike conventional hot air ovens, which are typically gas-powered, the concentrated sunlight roasts the coffee without heating the air around it by penetrating the grains in a more uniform way and without burning the exterior.

In a sunny day, a plant with 40 mirrors is capable of roasting up to 30,000 kilograms of coffee a year, saving about 60,000 kilowatt-hours of electricity.