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.