Effect of dasher design and processing conditions on residence time distribution of ice cream produced with a continuous scraped surface freezer

Abstract

The dasher assembly in scraped surface freezers (SSFs) plays a crucial role in the manufacture of ice cream by providing mixing during processing, removing ice from the heat exchange surface as it forms, creating fat structures, and incorporating air. Even so, very little is understood about how the design of dashers impacts frozen dessert development in SSFs. In this study, the effect of dasher design and processing parameters on the residence time distribution (RTD) of ice cream made in a continuous SSF was investigated. Processing parameters investigated included dasher speed, overrun, and throughput rate, while five dasher designs of varying geometries and volume displacements within the freezing cylinder were employed. Dye pulse injection studies were used to determine RTD properties while monitoring processing conditions including draw temperature, overrun, and amperage drawn on the dasher motor. Mean residence time was primarily driven by throughput rate, followed by dasher assembly, and then overrun. Reduced mean residence time was associated with higher throughput rates, higher dasher displacements, and lower overrun. Dasher rotational speed did not have a significant effect on mean residence time. There were two-way interaction effects between dasher design and dasher rotational speed, overrun, as well as throughput rate on residence time parameters (mean and/or variance). This study provides insight into the importance of dasher assembly design on the residence time and flow properties of a three-phase system in an SSF.