This section is from the book "Mrs. Allen's Cook Book", by Mrs. Ida C. Bailey Allen. See also: The Conscious Cook: Delicious Meatless Recipes That Will Change the Way You Eat.
In order to prevent "soaking fat" all foods cooked in deep fat should contain, or else be coated with, some albuminous substance, such as egg or milk. As heat has the power of hardening albumen at once (as in the frying of eggs) a coating is immediately formed through which the fat cannot penetrate, if it is of the right temperature.
In making croquettes it is customary to prepare the mixture, form it into any shape desired, roll it in crumbs or flour, then in egg whites and water (1/4 cupful of water mixed with an egg white will cover six croquettes) and again in crumbs or flour. (A half tablespoonful of gelatine, softened and dissolved in a half cupful of boiling water, may be substituted for the egg.) With egg, dry, sifted bread crumbs are used, while flour or meal is combined with milk as either will absorb the excess liquid. Either combination forms a delicious thin crust, through which the juices of meat, for instance, cannot escape, any more than the fat can enter. Care must be taken absolutely to cover every part of the croquette with the coatings, or the fat will enter at the exposed part and cause the croquette to burst.