Forced Air Cooling of Packaged Strawberries

To avoid decay of strawberries, it is important to cool strawberries quickly after harvesting and to maintain refrigerated conditions during distribution. In recent years, one-pound clamshell containers with hinged lids have replaced many of the open-top pint containers. In addition, there is an increased retail demand for a standardized larger tray that fits into a five tray per layer pallet configuration. The strawberry industry is interested in package designs that maximize cooling rates. In this study, cooling rates for pallets of packaged strawberries were determined at commercial forced air cooling facilities. Eight different treatments were tested consisting of strawberries packaged in different clamshell container and tray designs. One packaging treatment had a six tray per layer pallet configuration, while the others were of a five-tray configuration. Five layers of fruit were used for each treatment. Cooling rates were determined by calculating both the 7/8th cooling time and the cooling coefficient. Air temperature was found to vary significantly during cooling, which impacted the 7/8th cooling time calculation. Therefore, the cooling coefficient, using the measured air temperatures at each time step, was found to be a better and more objective method. Cooling rates were significantly faster for the sixtray configuration than for the five-tray configuration. These results can be used to help design better strawberry cooling tests and strawberry containers for faster cooling rates. If the air temperature cannot be held constant during cooling, the cooling coefficient based on instantaneous air temperature may be a better means of comparison than the traditional 7/8th cooling time.