Abstract
<b>Highlights</b> <list list-type=bullet><list-item> The SMER<i><sub>hp</sub></i> and SMER<i><sub>ws</sub></i> values for this heat pump drying system were 0.960 and 0.719 kg kWh<sup>-1</sup>, respectively. </list-item><list-item> A non-heating period in the heat pump dryer working cycle may affect the asynchronous negative drying rates of coffee in different layers in the drying chamber. </list-item><list-item> Results indicated that ambient air conditions might affect drying behavior in an open-loop batch-type heat pump dryer. </list-item></list> <b>Abstract</b>. Coffee is an important commercial crop in the world due to its popular flavor and aroma. The critical step in coffee processing is drying, which determines the coffee quality and market value. The most popular coffee drying techniques at present, sun drying and mechanical drying, have inherent disadvantages. In contrast, heat pump drying has been observed to offer higher energy efficiency and produce higher-quality output. Therefore, the objective of this research was to investigate the drying characteristics of coffee in a batch-type heat pump dryer. A total of 370 kg (0.72 m3) of fresh coffee at 70.01% ±1.26% (w.b.) moisture content was dried in an open-loop batch-type heat pump dryer. Samples were collected from six different horizontal layers in the drying chamber and two vertical sampling points. The average moisture content of three replicates was recorded. Wet basis and dry basis moisture content, drying rate, moisture ratio, color, temperature, and relative humidity of the ambient air and outflow air were measured and recorded. The SMERhp and SMERws values for this heat pump drying system were 0.960 and 0.719 kg kWh-1, respectively. The ÎE value for coffee at 10.11% ±0.42% (w.b.) moisture content was 31.65. These results indicate that the ambient air conditions may affect drying behavior in an open-loop batch-type heat pump dryer. Further studies are needed to identify the impact on aroma and flavor when processing coffee in a heat pump drying system to rationalize the advantages of using heat pump drying for coffee.
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