Mechanisms of Ice Crystallization in Ice Cream Production

Abstract

The smoothness and perceived quality of an ice cream depends in large part on the small size of ice crystals in the product. Understanding the mechanisms responsible for producing the disc-shaped crystals found in ice cream will greatly aid manufacturers in predicting how processing and formulation changes will affect their product. Because ice cream mix is opaque, it has not yet been possible to observe ice crystallization in ice cream in situ. Studies to date, therefore, have used analogues or have related observed effects to a hypothesized mechanism. Still, some elements of the crystallization mechanism are well accepted. Because of the large supercooling at the freezer wall, ice nucleates there before being swept into the bulk of the freezer. In the bulk, heat and mass transfer cause some crystals to melt and others to grow. By the time the ice cream reaches the freezer exit, the ice crystals have become small, rounded discs.

Online ice crystal size measurements during sorbet freezing by means of the focused beam reflectance measurement (FBRM) technology. Influence of operating conditions

“…During the initial freezing step, the mix is pumped through a scraped surface heat exchanger (SSHE) or freezer. The evaporation of the refrigerant fluid in the jacket of the freezer cools down the temperature of the mix below its freezing point, and causes formation of an ice layer at the wall of the freezer barrel (Cook and Hartel, 2010). Subsequently, the scraper blades of the rotating dasher remove the ice layer from the freezer wall.…”

Effect of freezing temperature and warming rate on dendrite break-up when freezing ice cream mix

“…When making ice cream in a small benchtop ice cream freezer with an open top (Cook, 2010), the slush layer was observed to be scraped off the wall as a continuous ribbon of slush was broken apart by the dasher and mixed in with the bulk of the ice cream. In this case, the ribbon of slush was a few millimeters thick, whereas in a commercial freezer, one might expect a thinner layer.…”

“…After hardening, the crystal size may range from 1 to 150 mm with an average of about 35 mm (Cook & Hartel, 2010). While the ice crystals in finished ice cream appear as discs, it is questionable as to whether discs are the original crystal shape formed in the freezer.…”

Multi-analytical approach for monitoring the freezing process of a milkshake based product

“…Water freezing into ice and incorporation of air are two complex steps that drastically affect the quality of frozen dairy desserts (Donhowe et al, 1991). During freezing in a scraped surface, the freezing process is very complicated phenomenon, as reported by Cook and Hartel (2010). The main parameters which affect the crystal nucleation and crystal growth are compositional and processing factors (Flores and Goff, 1999).…”