Solar Cooking
Last edited: 9 November 2021      

Coffee is one of the most popular drinks in the world and is one of the global economy’s most highly traded items, second only to petroleum. (Uncommon Grounds Specialty Coffee, 2006) Each year, about seven million tons of coffee beans are produced worldwide, contributing to the 400 million cups of coffee consumed by Americans everyday. (E-imports, 2007 and Gourmet Coffee Club, 1999)

Despite being a profitable export, coffee production is a very energetically costly process. After coffee beans are picked, they must be dried and then roasted to produce brown beans used to brew beverages. During a coffee bean’s journey from the plant to your cup, large amounts of fossil fuels must be burned for electricity, trees cut down for fuel, and natural gases expended to power coffee bean drying and roasting.

Coffee Drying[]

Before coffee beans are shipped, they must lose about 50% of their moisture content in order to maintain their quality. The coffee bean drying process has changed little from the introduction of coffee as an industrial agricultural product. (Coffee Research Institute, 2001-2006).

Beans are typically dried for 5-15 days on a cement or plastic patio exposed to the sun. After this initial period, the beans are transferred to a mechanical dryer for about six hours. The mechanical dryer is used to speed up the drying process in order to prevent coffee bean fermentation during this final and slowest part of the drying process. Dryers are generally powered by electricity or fuelwood. Mechanical dryers are not used in all countries but are often necessary in tropical, humid climates to prevent bean loss to mold and bacteria. (Coffee Research Institute, 2001-2006).

Industrial Solar Coffee Drying Systems[]

The process of drying coffee beans is one of the most expensive aspects of coffee production. Nearly 84% of the energy required for coffee production is used during the drying process. Coffee producers must use electricity generated by fossil fuels or wood fires to dry coffee beans before shipment. It has been estimated that for each cup of coffee we drink, there is a loss of three square centimeters of forest which has been used for fuel to dry coffee beans. The large-scale use of fuelwood for drying results in the destruction of over six thousand hectares of forest a year in Mesoamerica alone. Besides the negative environmental impacts of massive deforestation for fuelwood, the expenditure of fossil fuels, and the subsequent release of greenhouse gases into the atmosphere; the energy expended during mechanical coffee drying greatly raises the cost of coffee both for the producer and the consumer. (MDI, 2004-2005)

Concern for this massive energy expense has prompted organizations such as the Mesoamerican Development Institute (MDI), the Global Environment Facility (GEF), the Costa Rican Electrical Institute (ICE), and the Solar Trade Corporation (STC) to create and support technology for sustainable coffee production.

In 1999, with financial support from the World Bank and the Global Environment Facility, MDI created one of the first solar powered coffee dryer called the Solar/Biomass Coffee Drying System (also called Café Solar). (MDI, 2005) Café Solar uses reflective mirrors which transfer heat to rotating barrels containing coffee beans. As opposed to 5-15 days drying on the patio, coffee beans dried using the Café Solar spend only one day drying on the patio. Thus, besides being better for Mesoamerican forests, Café Solar decreases the likelihood that bacteria and mold will ruin portions of the beans since they do not spend as much time slowly drying on a patio. These solar-powered coffee dryers use only one-tenth the electricity as conventional coffee dryers and eliminate the need for fuelwood entirely. As a result, energy prices for coffee farmers decrease by about 90 percent. (MDI, 2004)

After creating Café Solar, MDI turned to its affiliated group, The Solar Trade Corporation, a Fair Trade organization founded in 1999. (World Resources Institute, 2006) STC manufactures and sells Café Solar to coffee farmers throughout Mesoamerica. With the help of STC and programs set up by GEF and the ICE, the solar-powered coffee drying system is being introduced and utilized by coffee farmers throughout Mesoamerica. (MDI, 2005)

Coffee Roasting[]

Coffee roasting is a process by which the chemical and physical properties of green coffee beans are changed to produce the roasted, brown coffee beans which we use to make coffee. As coffee beans absorb more and more heat, their color shifts from yellow, to light brown, to a dark, oily color. First, green coffee beans are dried in low-heat (about 188 degrees C) until they take on a light yellow color. As temperatures increase to 205° C, the beans expand to double in size and turn a light brown color. When the roaster reaches 220° C, the beans become a medium brown. The final step of the coffee roasting process is reached when temperatures rise to 225-230° C: the beans become a darker brown color with an oily sheen. This process can take anywhere from 5-30 minutes. (Coffee Research Institute 2001-2006)

Traditional coffee roasters are typically horizontal rotating drums which consist of a combustion chamber and a connected roasting oven. The combustion chamber is generally fueled by natural gas which circulates through the roasting oven to heat the beans. (Coffee Research Institute 2001-2006)

Although the combustion of natural gas results in the release of CO and CO2, natural gas is relatively clean-burning and emits low levels of potentially harmful byproducts into the atmosphere. ( , 2004) However the sharp rise in demand for natural gas has led to price spikes, increased drilling on public lands, and less environmentally-sustainable gas exploration/extraction practices. (NRDC, 2005)

Solar coffee roasters[]

In the past 15 years, numerous coffee companies have taken action to create more sustainable techniques that don’t require expendable resources; including the invention of solar-powered coffee bean roasters. In July of 2004, two brothers named Mike and David Hartkop began designing one of the first solar coffee roasters. This original roaster eventually evolved into what the brothers use today: a 12-foot-tall square covered with reflective materials which can swivel in a complete circle to follow the sun. The device reflects about 140 square feet of focused light onto the drum roaster (which contains the roasting beans). The outside of the drum can reach temperatures of 1,200° C and can roast about five pounds of coffee beans at one time. (, 2007)

Another experience of coffee roasting started in 2012 in Peru. The solar roaster has been developed by the Grupo de Apoyo al Sector Rural from University PUCP, Peru. It is designed for rural use in order to enable coffee growers to roast themselves their production. (Alors, on change, 2013/9)

Articles in the media[]

See also[]