Final answer:
When making ice cream with the plastic bag method, shaking the bags for five minutes helps churn the ice cream while cooling it evenly.
Step-by-step explanation:
In order to make ice cream with a plastic bag method, the mixture is placed in one bag, surrounded by another bag half full of ice with salt added to lower the temperature of the ice/salt mixture.
Shaking the bag for five minutes churns the ice cream while cooling it evenly.
During this process, heat is transferred from the ice cream mixture to the ice, causing a phase change.