When making Ice Cream, why should the can containing the milk mixture be made of metal?

ice cream lid image

ilovejohnm

When making ice cream the milk mixture is placed inside a medium sized metal can with a lid. What does that do? Also, which takes longer, making ice cream in metal cans or plastic bags? and Why?

Answer
Metal gets colder than plastic and you have to et the ice cream mixture cold.

A plastic bag? You have to keep stirring the ice cream mixture so as to not have ice crystals form in the mixture.