We studied the kinetics of drying apples of the apple-tree 'Jonagold' variety – broken up into rings of the diameter of 20 mm, and thickness, respectively: 3, 4, 5, 7 and 10 mm – in the temperature of 55 C, at the drying air flow velocity of 0,5 m s-1, and determined the thermometer temperature of wet drying air. The apple ring drying process was carried out in forced convection conditions, from the initial moisture content of 85%, until the examined raw material reaches the moisture content of 16%. Using study results, we defined, with assumed relative error not exceeding 5%, the duration of first drying period for particular thickness of apple rings, which was, respectively: τI (3 and 4 mm) = 2700 s, τI (5 mm) = 3600 s, τI (7 mm) = 5400 s, τI (10 mm) = 7200 s. On the basis of the performed variance analysis, we found a significant influence (on the significance level α = 0,05) of apple ring thickness on the duration of first drying period, and with the increase of apple ring thickness the duration of the first period of convection drying becomes longer.