Overrun in Ice Cream
Incorporation of air into ice cream, termed the overrun, occurs
at this stage. Some overrun is necessary to produce desirable
body and texture. Two main types of air incorporation systems
are used in continuous freezers. In older systems, the pump
configuration resulted in a vacuum either at the pump itself or
on the mix line entering the pump. Air was then incorporated
through a spring-loaded, controllable needle valve. Newer types
of freezers use compressed air, which is injected into the mix.
This type of air handling system allows for air filtration
(0.65 mm micropore filter) prior to admission into the mix.
Following aeration, the water in the mix is partially frozen
as the mix and air combination passes through the barrel of the
heat exchanger. Ice forms on the inside wall of the heat
exchanger from the water in the mix, resulting in a freeze