Dew point undershoot mechanisms driving surface condensation in commercial apple cold storage

Monitoring and controlling surface condensation on fruit is a crucial factor to maintain quality and reduce postharvest losses during cold storage. High air humidity can cause liquid water to condensate on the surface of fruits, stimulating the growth of spoilage organisms and contributing to fruit losses. At the same time, short condensation intervals can be beneficial for preventing moisture loss and limit weight loss of the fruit. According to psychometrics, condensation forms whenever the fruit surface temperature falls below the dew point of the surrounding air, a condition defined as the dew point undershot (DPU). Because direct measurement of condensation is challenging; we applied an indirect approach by continuously comparing fruit surface temperature with the calculated air dew point from ambient air temperature and relative humidity sensors. Condensation forms during DPU events and remains on the fruit surface until all condensed water is evaporated. Using this method in a commercial 50 t apple cold room, five distinct mechanisms that triggered DPU and subsequent condensation, were experimentally verified. These conditions include door openings, loading of warm fruit, defrost cycles, ventilation-driven air mixing and slightly cooler bins in the bottom tier. Condensation risk was mostly observed in the highest tier, in the door-side bins and occasionally interior stacks. These insights will provide the necessary basis for targeted monitoring and operational strategies to minimize condensation-related decay while maintaining high humidity to reduce weight loss. • Condensation was monitored in 50 t apple cold storage room. • Using dew point and fruit surface temperature to predict condensation. • Five different types of dew point undershoots were identified experimentally. • Condensation mostly occurs in door side and top bins, but also deeper in the stack. • Adjusting setpoints and ventilation times reduces condensation risk.