S23 - Session O2 - Water vapour condensation periods on fruit surfaces during CA storage of apples

Authors: Ulrike Praeger *, Manfred Linke, Daniel A. Neuwald, Martin Geyer

Temperature and humidity fluctuations occur in apple storage rooms with every cooling cycle due to the operation of the refrigeration system with direct evaporative air coolers. As a result, the temperature on fruit surfaces can temporarily fall below the dew point, causing condensation. Moisture on the fruit surface can influence the mass transfer, however, the extent and impact on fruit quality during long-term storage is unknown. The aim of this study was to examine the recurrent condensation that forms on apple surfaces and the duration of condensation in relation to the operation of the refrigeration system. In an apple CA storage room (50 t), the condensation periods were determined in different cooling cycles. Cooling and re-warming phases without disruption were compared with cooling cycles superimposed by defrost processes. For this purpose, the duration of the active condensation and subsequent evaporation phase was qualitatively determined on the surface and in the fruit bulk of a bin in the supply air area of the room. Active condensation occurred only during rewarming of the fruit surface, while during the cooling phase, the fruits still were wet due to the subsequent evaporation phase. During short cooling cycles with defrosting in the cooling phase ( < 1 h), the fruit surfaces were covered with condensate all the time. During longer cycles without disruption by the defrost process ( > 2 h), moisture on fruit surfaces occurred about 30 % of the time. Thus, the fruit in the supply area of the room had wet surfaces over more than one-third of the storage time. The influence of the fruit position, refrigeration and fan operation and the defrost processes are discussed. Additional measurements of fruit mass loss and air velocity in bins at different positions suggest that similar mass loss throughout the store was caused by a compensating effect of condensation in the supply air area of the room.