Browsing by Author "Diaferia, Francesco"
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- Physical properties of coffee related to the roasting processPublication . Diaferia, Francesco; Vieira, Érica Nascif Rufino; Gomes, Ana Maria PereiraRoasting is one of the most important processes regarding the final quality and physical properties of coffee. This work was done with the aim of analyzing the change in the physical properties of coffee during the roasting process. More specifically, the variations of the orthogonal axes, the circularity, the sphericity, the mass loss and the surface and volumetric expansions of the coffee beans subjected to the roasting process were analyzed. The Arabica coffee variety was classified in shape and size using a sieve. The samples were then stored in polyethylene bags in refrigeration chambers at 18 °C to maintain the initial characteristics before roasting. After that, roasting was carried out at the temperatures of either 220, 240, 260, 280 or 300 °C over a period of 600 seconds. Specifically, the rotary cylinder direct gas firing roaster, used at 45 rpm, was held for 10 min at one of the respective roasting temperatures (220, 240, 260, 280, 300 ºC) in each case. The air temperature was measured by a type k thermocouple positioned inside the cylinder and controlled manually with a gas step valve. Five air temperatures were set inside the cylinder. The surface temperature was measured by an infrared thermometer (Testo 830-T1). The experiment was performed with 3 repetitions for each temperature and each sample. Every 20 seconds, 10 grams of coffee beans were taken from the roaster and measurements were taken using a caliper rule, in order to obtain the dimensions of the beans. In general, the physical parameters analyzed were evidently affected by temperature, the impact being more significant at higher ones. Graphically, the differences in terms of distance between the thermal curves are shown on average starting from 400 seconds, to then stabilize at the end of the process. In general, the parameters of sphericity, circularity, mass loss, surface expansion and volumetric expansion show linear increases over time.