Answer to Question 1
Overrun is the volume of frozen dessert obtained in excess of the volume of the mix, and is due to both expansion of water as it crystallizes and to the air incorporated into the mix. Overrun is of interest because of its relationship to yield and because of its influence on mouthfeel and texture.
Answer to Question 2
An ice and rock salt mixture is used to remove the heat from the ingredients in the canister so the ingredients start to freeze. A metal container enhances the efficiency in transferring heat out of the canister and promotion of crystal formation.
