The constant rate drying period during experimental fruit drying.

Clingstone peaches (63 mm. diameter) were pitted, peeled and subjected to a blanching treatment. Dehydration was performed as counter-flow simulations programmed from 58.0 degrees to 67.0 degrees C at wet bulb temperatures of 39.6 degrees, 45.0 degrees and 49.5 degrees C. Bon Chretien pears (count 8 8) were peeled, halved, cored and immersed in a 2% (m/v) aqueous sodium chl oride solution for two minutes. Dry bulb temperature was programmed from 48 .0 degrees to 60.0 degrees C. Wet bulb temperatures of 34.9 degrees and 39. 7 degrees C were used. Granny Smith apples (+/- 72 mm. diameter) were peele d and cored prior to cutting in rings (8 mm. to 9 mm. thick). The rings wer e subsequently dipped in sodium metabisulphite solution (3% m/v, 2 min.). C ounter-flow simulations were performed by programming dry bulb temperature from 58.0 degrees C to 74.0 degrees C. Dehydration was performed at two hum idity levels corresponding to 55.2 degrees, 50.3 degrees and 44.2 degrees C wet bulb temperature respectively. Constant rate drying was observed in all cases at the higher wet bulb tempe ratures for peaches (49.5 degrees C), pears (39.7 degrees C) and apples (55 .2 degrees C). Thus constant drying rates could be expected during commerci al counter-flow drying of fruit where air humidity is often maintained at e levated levels in the interests of economy. The occurrence of constant rate drying has implications with regard to enzymatic reactions in unsulphited products as well as loss of sulphite from the product during drying.