Influence of freezing conditions on ice crystallisation in ice cream

Abstract

Successful optimisation of the ice cream freezing process to deliver a product with small ice crystals, and therefore a smooth texture, requires an understanding of the mechanisms of ice crystallisation. The purpose of this work was to relate the processing variables available to the ice cream manufacturer to measured ice crystal size distributions, with a view to elucidating the dominant crystallisation mechanisms within a scraped surface ice cream freezer. It was found that ice crystallisation within the freezer is dominated by recrystallisation processes such as aggregation and dissolution/growth. These mechanisms appear to be more important than nucleation in determining the final crystal population. Crystal coarsening by recrystallisation in the freezer can be minimised by reducing product residence time. Increasing dasher speed causes an elevation in product temperature, through increased dissipation of frictional energy, which leads to dissolution of small crystals and enhanced crystal aggregation, giving larger crystal sizes in the exit stream.