2.2. Experimental set-up
The schematic of the experimental microwave drying set-up is given in Fig. 1. The microwave oven was operated by a control terminal which could control both microwave power level and emission time. The dimensions of the microwave cavity (M945, LG Samsung) were 327 · 370 · 207 mm. In order to weigh the samples without taking them out of the oven, a weighing sys- tem was integrated to the oven. A digital balance (GF-600, A & D, Japan) which has a sensitivity of 0.01 g and a plastic disc was mounted to the bottom of the microwave oven. The disc was rotated at 5 rpm on a ball bearing shaft driven by an elec- trical motor. The presence of the rotating disc was necessary to obtain homogeneous drying and to decrease the level of the reflected microwaves onto the magnetrons. The oven has ventilation holes on the top as well as on the bottom. Air