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Drying and disinfection of off-ground harvested almonds using step-down temperature hot air heating

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2021 ASABE Annual International Virtual Meeting  2100267.(doi:10.13031/aim.202100267)
Authors:   Chang Chen, Chao Liao, Ivan Wongso, Wenbin Wang, Ragab Khir Abd El Gebreil, Zhaokun Ning, Guangwei Huang, Franz Niederholzer, Luxin Wang, Zhongli Pan
Keywords:   Almonds, Off-ground harvest, Step-down temperature drying, Hot air, Disinfection, Quality assessment.

Abstract. The objective of this study was to develop a simultaneous drying and disinfection method for off-ground harvested almonds to improve drying energy efficiency and product safety. Drying experiments were conducted in a column dryer (0.57 m height) under constant temperature hot air heating (ambient, 40, 50 and 60°C) or step-down temperature heating conditions (preheating with 80°C and 90°C) with holding for 1, 2 and 3 h, and then finishing drying at 60°C at an air velocity of 1.0 m/s. The drying time ranged from 4 to 36 hours to dry almonds from their initial moisture content of 0.41 kg water/kg wet mass to a targeted 0.12 kg water/kg wet mass almond moisture. For quality, no cavity, significant color change, significant concealed damage and deterioration of oil quality were observed under all tested conditions. The specific energy consumption ranged from 14.3 to 22.0 MJ/kg under the test conditions. The step-down temperature hot air drying with holding achieved up to 0.8 log CFU/g reduction in the total bacterial counts of in-shell almonds. Drying in-shell almonds saved 75% drying time and 10% energy consumption compared to drying in-hull almonds under the same temperature with more uniform final moisture distribution. The findings suggested that off-ground harvested almonds should be sorted and de-hulled prior to drying, which could significantly improve the drying efficiency, moisture uniformity and throughput of the drying process.

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