This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The chief factors governing the amount of fat which will be absorbed by a food during frying are (1) the time of cooking, (2) the temperature of the cooking fat, (3) the total surface area of the food, and (4) the composition and nature of the food.
Time of cooking. In general, it can be stated that the longer the food is cooked the greater the fat absorption. There will be some exceptions to this. For instance, with some foods cooked at high temperatures, coagulated material or a hardened crust may prevent greater fat absorption with longer cooking. Other foods which contain a high percentage of fat like breaded pork chops may lose fat during cooking. This is also true of fried chicken, if the chicken has a high fat content.
Temperature of cooking fat. Usually there is less fat absorption at higher cooking temperatures. This is probably due to the quick formation of a crust or coagulated material at the high temperature. However, slight differences in cooking temperature, 30° to 40°C, cause little variation in fat absorption. Ordinarily food is cooked at moderate temperatures to thoroughly cook the food without excessive browning.
Surface area. The larger the surface for a given weight of material the greater the area over which fat may be absorbed. Cracks caused by handling or expansion in cooking, rolling thin rather than thick, roughened surfaces, due to little mixing or other causes, stretching and pulling the material out of shape in handling, all increase the surface area and thus tend to increase the fat absorption.
The composition and nature of the food. Some foods by their nature tend to absorb more or less fat than others. For example, fried eggs may absorb less fat than some foods. This is due to the smooth surface and to the coagulation of the egg proteins, which tends to prevent fat absorption. Large amounts of flour on the surface of chops may tend to increase the fat absorption, owing to the absorption of fat by the flour. Variations in composition of the food and variations in the proportion of ingredients used in foods cause wide variations in the amount of fat absorbed. A food like doughnuts, containing sugar, fat, liquid, eggs, flour, and baking powder, may show wide variations in the amount of fat absorbed, even when the length of time of cooking and the amount of surface area are kept as standardized as possible. Variations in the extent of mixing foods like doughnuts produce variations in the amount of fat absorbed during cooking because the characteristics of the dough are altered by mechanical treatment.