A solar-powered drying system that combines greenhouse design with active air circulation could offer coffee producers a more reliable and lower-emission way to process beans after harvest, according to research in the International Journal of Exergy. The conclusion comes from a smooth blend of laboratory modelling and field trials.
Drying is a critical step in coffee production. Freshly harvested coffee beans typically contain more than 50% moisture. That level must be reduced to about 10% to mould growth and spoilage. Beans that are unevenly dried produce poorer-quality coffee if any coffee at all.
The system looked at the benefits of drying beans in a greenhouse-type structure that traps solar radiation. Such greenhouses can get hotter than conventional drying areas, leading to faster evaporation from the beans. The use of solar-powered fans is needed to move air through the drying chamber, reducing humidity and giving even drying, the researchers suggest.
Trials of this approach demonstrated that beans could be dried from about 50% moisture to close to the requisite 10% in just four days. This meets industry standards for safe storage and transport, the report explains. Key to success is consistent temperature control. Too hot and the flavour compounds in the beans can degrade. If the system is not hot enough then slow moisture loss leads to spoilage.
The study showed that a drying temperature of 52.5 Celsius is optimal, just right for consistent moisture removal without flavour compound compromise. Energy and exergy measures of the process showed an efficiency of 33% and 40%, respectively. The energy efficiency is less representative than the exergy measure. Exergy shows how much useful work is done in the process rather than dissipated as waste heat. A higher exergy efficiency means the system is making better use of the available resources. This is an important consideration in renewable energy applications and environmental audits.
Ayala Gonzáles, J.R., Marcelo-Aldana, D. and La Madrid Olivares, R. (2026) ‘Performance evaluation of a solar greenhouse dryer for coffee drying in the Peruvian high Andes: an energy, exergy, economic, and environmental approach’, Int. J. Exergy, Vol. 49, No. 4, pp.318–333.
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