THERMAL BEHAVIOUR OF DIFFERENT TYPES OF COMMERCIAL COFFEE AND RESULTING COFFEE GROUNDS IN INERT ATMOSPHERE. THE INFLUENCE OF COMPOSITION (ARABICA AND ROBUSTA)

This paper aims at analysing the thermal behaviour of six types of commercial coffee and the coffee grounds resulting from their use in a professional DeLonghi coffee machine. The influence of composition (Arabica and Robusta) on the thermal behaviour was thus highlighted for the first time. The obtained results indicate that the degradation occurs in three or four stages, based on the composition. The first stage consists in water removal, which can be found in a percentage of 1 up to 5%. The thermal decomposition of the samples starts at temperatures higher than 230 °C, in the case of both different coffee types and coffee grounds. By comparatively analysing the temperature values at which the degradation starts, it can be noticed that in all the cases there is an increase in the thermal stability of the coffee grounds with approximately 20 degrees, compared to the coffee types they come from. For coffee grounds originating from coffee that contains 35% Arabica and 65% Robusta, the degradation mechanisms change at temperatures higher than 320 °C, as confirmed by the occurrence of an additional degradation stage, compared to the case of other samples. The obtained DSC curves emphasized the presence of two melting peaks and one crystallization peak, which, according to the specialty literature, indicates the presence of coffee oil.