A specialty type of refrigeration system found in some food service businesses is the soft-serve ice cream freezer. These systems are designed to inject an ice cream mix with the correct amount of air, and freeze the mixture to its specific consistency or temperature.
The basic system consists of a hopper, mix feed system, beater, and freezing cylinder. The hopper is a refrigerated holding tank for the ice cream mix. It’s designed to maintain the mix at a safe storage temperature. Connected to the hopper is the mix injector. As needed, the mix will be injected into the freezing cylinder. Air, called “overrun,” must be added to the mix. This is essential to the consistency of the product. Most machines have an adjustment on the mix feed system to adjust the amount of overrun. Some machines have a fixed overrun, set at the factory, for the particular mix being handled.
As the mixture (ice cream mix and air) enters the freezing cylinder, it freezes to the walls of the cylinder, and the beater (sometimes referred to as an auger) scrapes the frozen mixture off the walls. This process continues until all the ice cream mix in the cylinder is at the proper consistency.
The beater assembly has three functions: scrape the frozen product from the cylinder, whip the product, and eject the product.
The beater blades must be kept in good condition and not be damaged during cleaning. Some machines use a beater assembly with removable plastic blades. Care must be taken when removing and replacing these beater blades during cleaning. These blades “wear in” and should not be interchanged.
There are several different refrigeration designs a manufacturer can use for its soft-serve machines. Some machines will use one refrigeration system to refrigerate both the hopper(s) and the freezing cylinder(s), while others will use a separate refrigeration system for the hopper(s) and the freezing cylinder(s).
The evaporator design slightly varies between the various machine manufacturers. Some manufacturers use a cylinder within a cylinder in which the refrigerant is fed from the metering device into the space between the two cylinders. Others use a cylinder wrapped with copper tubing. In this design, the refrigerant is fed from the metering device into the copper tubing wrapped around the cylinder.
There are several different methods a manufacturer can use to determine when the ice cream mix is at the proper consistency and ready to be dispensed. Some machines monitor the temperature of the ice cream mix. When the mix is at the correct temperature, the beater assembly and the refrigeration system are cycled off. Monitoring the low-side pressure of the refrigeration system also can be used to determine when the ice cream mix is at the right consistency; a pressure control is used to cycle the beater assembly and refrigeration system at a specific pressure.
Another method used by manufacturers is to directly monitor the consistency of the product. As a product begins to freeze, it requires greater force for the beater or auger to move through the ice cream mixture. This additional force, called torque, is measured by the control system so as the product begins to freeze and thicken, the refrigerant cycle can be terminated. This can be determined by either mechanical means, such as a split clutch assembly or by monitoring the amperage draw of the beater motor.
The draw rate, which is the amount of ice cream that can be removed from the freeze cylinder over a specific time, is limited by the machine’s individual capacities. If the designed draw rate is exceeded by the user, the product will be too soft to stand up and, therefore, be unsatisfactory.
Maintaining and servicing these systems is not difficult, but it does require specific knowledge of the machine’s design and operation. Most technicians servicing these systems will have attended one or more training sessions to become well-versed in their required service procedures.
Publication date: 6/1/2015