The slow cooking give confit meat its texture and the storage time allows further reactions and dissolutions to take place. The traditional reason solid fats have been used for a confit is for preservation: once the fat cools it "seals" the meat. Today we can refrigerate, so many restaurants now make their confit with liquid oils.
Myhrvold has demonstrated that he can reproduce the duck confit by using a steam and air mixture to cook the duck leg and then flavor its surface with oil.
There are several processes competing when we heat meat to cook it:
- The collagen needs to melt and gelatinize. There are different types of collagen, each denaturing in different temperature ranges. As the meat is heated, collagen starts to shrink at about 40°C/ 104°F and by 80°C/176°F all of it is gelatinized. Different animals have different types of collagens and the right temperature could be anything between 60°C/140°F and 80°.
- The elastin, which exists in smaller quantities than collagen, will shrink with temperature and make the meat tougher.
- As the many molecules contract, they squeeze water from the meat, making it feel tougher.
So if you are going to develop a recipe, you will have to experiment. As a guide, the more collagen, the higher temperatures you will need. The amount of collagen goes up with the age of the animal and how much weight (stress) the muscle needs to support.
The reason confits are made by immersing the meat in oil may be that the oil makes it harder for the meat to loose its water, but I speculate.
Cooking for Geeks is one of the few places I found discussing the science of confit. Maybe Myhrvold's slim tome will have a section on it.