This section is from the book "A Book Of Recipes For The Cooking School", by Carrie Alberta Lyford. Also available from Amazon: A book of recipes for the cooking school.
Many foods do not become covered with a crust when subjected to high heat in deep fat. Such foods must have some egg added to the mixture or be coated with a substance which forms a crust quickly. For this reason foods are dipped into bread crumbs and eggs, a method known as egging and crumbing.
Dried crumbs are prepared from crusts and from small pieces of hard bread dried in a very moderate oven until a light brown. Roll them on a pastry board, or put them through a meat grinder. Sift the crumbs. Keep dried crumbs in jars, tie pieces of muslin over jars and keep in a dry place. Use them to cover articles of food to be cooked in deep fat. For savory dishes it is well to season crumbs with salt and pepper.
1 Dip article into seasoned dried bread crumbs, flour, or corn meal, covering it entirely with crumbs.
2 Dip into egg which has been slightly beaten with 1 tablespoon water, milk, or oyster juice(for fried oysters).
3 Dip again into seasoned bread crumbs.
Reasons for steps in egging and crumbing for deep fat frying:
The article is dipped into bread crumbs
1 To make the surface dry.
2 To cause the egg to adhere. The article is dipped into egg
1 To cause a crust to form on the surface.
2 To prevent fat soaking in.
Water is added to the egg(l tablespoon to each egg)
1 To prevent its becoming dry and stringy.
2 To prevent cracking of the crust. The egg is beaten slightly
1 To mix it well and break up the membrane.
2 To avoid large bubbles in cooking, as they might crack and admit fat. The article is dipped in crumbs the second time
1 To make the surface drv so that the fat will not bubble so vigorously.
2 To improve appearance and flavor of the crust.