Effect of temperature variation on ice cream recrystallization during freezer defrost cycles

Ice cream quality is influenced by temperature fluctuations during storage which cause ice crystal growth or recrystallization. Minimum temperature fluctuations occur during normal freezer on-off operation. However, large temperature variation may occur during the freezer defrost process which aims to melt accumulated ice on the freezer cooling coil. In this work, an experimental study was conducted to measure the temperature fluctuations inside two walk-in freezers of different sizes during normal and defrost operating conditions. Numerical simulations were carried out to examine the ice cream response to the temperature fluctuations inside the freezers using transient heat transfer model with variable boundary conditions. The data showed that the defrost timing and the maximum elevated temperature during the defrost process are strongly related to the freezer size and refrigeration unit specifications. Based on the ice cream response to the freezer temperature fluctuation and times of exposure, ice recrystallization rate and frozen water content are discussed and linked to the deterioration of the ice cream quality for two different ice cream formulations.