PPT Slide
The dissolved sugar, by getting in the way of the molecules that bond together to form ice crystals, lowers the freezing point of the cream/milk. At the new, lower, freezing temperature, the water molecules are removed from the solution as they crystallize. This leaves the remaining solution greater in sugar concentration� thus depressing its freezing point even farther.
It should be clear from this trend that the liquid phase of ice cream will never completely freeze. The lower the temp., the less liquid� the harder the ice cream� the more concentrated� and the lower its new freezing point. (Soft ice cream�-6 Centigrade�50% water; Hard ice cream�-18 Centigrade�20% water)
Salt reduced the freezing point of water, When salt is added to ice, heat is absorbed by the ice to melt. The surrounding liquid gets colder�as it is the environment that provides (gives up) the heat energy.
Kneading/churning provides tiny pockets of air and prevents large crystals from forming in the ice cream.