From On Food and Cooking:
Ice cream is a foam that is stabilized by freezing much of the liquid. When examined under a microscope, it reveals four phases....
Each phase makes its own contribution to the character of the ice cream. The liquid (kept liquid primarily by the dissolved sugar, which lowers the freezing point) prevents it from being a solid block of ice, while the substances it carries bring flavor, nutritional value, and, in the case of the proteins, body and foaming aid. The solid ice crystals stabilize the foam by trapping the other phases in their interstices, and the fat provides richness, smoothness, and body. The air cells, though nothing in themselves, perform the important service of interrupting the solid and liquid phases, and so making the whole mixture softer and lighter. Ice cream without air cells is very difficult to scoop and bite into.
He goes on to say that rapid cooling of the base with constant movement helps prevent the creation of large ice crystals and thus produces a smoother product. Commercial producers can freeze the product in a matter of minutes and shoot in compressed air to bypass the slow process of creating overrun that us home makers have to endure.
He gives these tips for the home ice cream maker:
1) For ultra-rich ice cream that is also that also has enough air to be scoopable, he suggests adding condensed milk, half and half, or dry milk to the base to increase protein without diluting the product. But beware, because these can also raise the lactose levels and result in lactose crystals and grittiness.
2) Bring the base down to 40 degrees before churning for a faster freezing and to avoid turning some of the fat to butter.
3) For hardening, place in multiple pre-chilled containers for faster freezing.
4) Ice cream should be stored between -10 and 0 degrees and well-covered (I always use a layer of plastic wrap pressed against the ice cream and then use a lidded container). Partial thawings and freezings result in an icy texture.
btw, earlier in the chapter he talks about stabilizers, such as gums. This has been of some interest to me primarily for sorbets which don't have the benefit of proteins and fats and must rely on sugar and alcohol for their texture. He notes, as I've learned, that such things can help as a replacement for sugar or fat, but can also result in a gooey texture and an off-taste. Compare the texture of Haagen Daz, which only has cream, milk, sugar, and eggs, to something with stabilizers, like some Cold Stone ice cream, and the difference in texture is immediately apparent. btw, my experience is that too much sugar results in the same thing, plus makes it burn-your-throat sweet.