The ice cream mixture starts off as a liquid. It's actually called an emulsion - this means it's a combination of liquids that don't usually mix together without separating. As it mixes and freezes in the ice cream maker, the fat particles in the cream spread through a mixture of water, sugar and ice crystals. The mixer also forms air bubbles within the ice cream, which makes it a foam! As the mixture freezes, the molecules get closer together, giving it a solid structure. Once you take it out of the freezer, the molecules heat up and move further apart to form a liquid, a process we call melting.