Physical and Experimental Studies of Coffee Drying Process With Thermal, Solar and Infrared Sources

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Addis Ababa University


Coffee drying experiment by thermal, by solar and infra radiator sources was done to determine the most appropriate and effective method. By using thermal the experiment has been done at three different temperature (50oC,60oC, and 70oC), it took 10h, 7h and 5h respectively. In solar drier it took about 24h. And by infra radiator the experiment is done at three drying voltages, 100V, 120V and 150V. It takes 9.5h, 7h and 3h respectively. The infra radiator is the most efficient out of all. A total of seven thin layer models were used for modeling. Statistical parameters such as the chi-square, root mean square error and coefficient of correlation (R) were used to assess the goodness of fitting. The best model describing the thin layer drying characteristic was chosen as the one with the highest R values, the lowest χ2 and SSE values. In all the drying experiments as compared to other thin layer models the Midilli Kucuk model was able to satisfy these criteria and chosen. The Midilli Kucuk model was found to be the best fitted model to describe the drying curves in all the experiments performed. If there is any change in some coffee chemicals that affect the quality of coffee dried in the experiment, the high-performance liquid chromatography was applied for the simultaneous determination of four coffee alkaloids in the aqueous extracts of the beans. the alkaloid of the coffee dried in the experiment analyzed and compared with coffee dried by the farmer at the pulping station. The concentration of caffeine higher in sample from Gimbi than from Sidama and trigonelline in samples from Sidama is higher than in Gimbi. The differences in concentration are due to origin of the coffee. No variation of alkaloids due to drying process was observed.



Caffeine, Drying, Heat and Mass Transfer, Mathematical Modeling, Moisture Content, Moisture Ratio