This study investigates the effect of agitation speed on the freezing process of ice cream using a batch freezer. The temporal change in apparent viscosity during freezing is measured by the Metzner-Otto method. It was found that the apparent viscosity of ice cream after freezing decreased with an increase in the agitation speed. In addition, the number of bubbles incorporated into the ice cream also increased with the increase in the agitation speed. The bubbles were broken down into smaller bubbles by the higher shear force, that is, the higher agitation speed. Furthermore, a narrower distribution of the bubble size was obtained at higher agitation speeds. This indicated that the rheological properties and the microstructure of ice cream can be controlled by the agitation operation. Practical applications This study clarified the effect of agitation speed on ice cream properties such as the apparent viscosity, the overrun and the size distribution of contained bubbles. Especially, the apparent viscosity is important for both industries and consumers. The Metzner-Otto method was used to directly measure the temporal change in the apparent viscosity during freezing. This temporal change has not been investigated so far. It was found that the apparent viscosity decreased with the increase in the agitation speed. In other words, the rheological properties can be controlled by the agitation operation. In industries, the continuous freezer is more preferable than the batch freezer used in this study. Nevertheless, the knowledge would be quite useful for the development of industrial processes of ice cream.