Microstructural evolution of ice cream after start-up in a continuous scraped surface freezer

Abstract

A continuous scraped surface freezer was used to freeze ice cream, with samples taken over time to monitor the development of ice crystals, air cells, and fat destabilization. Microscopy methods were employed to determine the size of ice crystals and air cells, while fat destabilization was measured via laser diffraction. Processing conditions including overrun, draw temperature, and the percentage of power drawn by the dasher motor, were monitored for comparison to microstructural development. The residence time distribution, or the range of times that ice cream spent in the freezer, was measured by pulsed dye injection, with mean residence time about 4.8 ± 0.2 min. Once the freezer was started, all system elements were stabilized within approximately 2–2.5 mean residence times, with some stabilizing within one mean residence time. Ice crystallization is likely a key driver of microstructure development, as ice formation results in increased product viscosity and shear forces, which promote air incorporation and fat destabilization. This study contributes to the understanding of microstructure formation of frozen desserts in continuous scraped surface freezers, particularly during start-up operations, where it is important to minimize waste.