Ice cream has been made essentially the same way since Nancy Johnson invented the hand-cranked freezer in 1846. A schematic of a typical commercial ice cream barrel freezer 10 is shown in FIG. 1. In a typical procedure, a scraper-dasher assembly having several scrapers 12 and a dasher 14 is rotated on its axis inside a refrigerated pipe 15. In the process, ice cream precursor (for example, cream) is passed through an annular space 16 between the dasher 14 and the refrigerated pipe 15. Air is injected into the barrel freezer so that it is incorporated into the cream. The cream freezes on the wall 18 of the pipe to form the ice cream, and is scraped off the walls by the scrapers 12. The size of the ice crystals and the consistency of the ice cream is influenced by the speed of the scrapers and the clearance between the scrapers and the walls. Since small crystals are desirable (for a higher quality creamy ice cream) the clearances between the blades and the walls are necessarily small. This, combined with the large forces on the dasher, can make the system somewhat expensive.
In addition, the crystals that have been scraped off the walls of the refrigerated pipe can grow under some conditions within the mixture in the volume of the annulus (for example, due to poor temperature control), and this effect can reduce the quality of the ice cream exiting the barrel freezer. The ice cream exits the barrel freezer, typically with the consistency of soft-serve ice cream, where about 50% of the water in the ice cream is in a frozen state. Subsequently, the ice cream is cooled, for example by passing it through a blast freezer to reduce the temperature of the mixture to, e.g., below about −25° C., to arrest the crystal growth process within the ice cream. In this process, the ice cream is generally hardened.
There are also continuous-feed auger-driven heat exchangers that can be used to post-process and cool the ice cream (e.g., below −25° C.) after processing of the ice cream within the barrel freezer. These systems typically physically break down the ice crystals in the ice cream even further, resulting in a creamier (and more desirable) ice cream. Because of high shear forces typically required in these devices, and the increasing effective viscosity of the ice cream caused via this process, these systems typically consume substantial amounts of power, and are relatively complex and expensive to build and maintain.
The relative uniformity of ice cream production, since its invention, provides room for modifications or improvements in this process and in ice cream and other frozen foods, such as frozen desserts.