Development of a tensiometric model for surface energy characterization of raw coffee beans

The aim of this work is to investigate surface energy properties of various raw coffee bean species (tensiometric approach) and to develop a tensiometric marker based on contact angle measurements of Fomblin HC/25 drops, a perfluoropolyether phosphate (PFPE), to distinguish different species of raw coffee beans. To create measurable contact angles, raw coffee beans were pre-selected according to the endosperm surface morphology (smooth surface) and affixed to a specifically developed support. The tensiometric method was developed using contact angle method (CA) and calculation models such as Owens, Wendt and Kaelble. Results show the tensiometric properties of raw coffee beans expressed as surface free energy (SFE) and the capability of the marker to distinguish species. This work could create interesting prospects for quality control at the product source, storage conditions, and for industrial process evaluation of roasting and drying.