This section is from the book "Twelve Lessons In Scientific Cookery", by Suzy Tracy. Also available from Amazon: Twelve Lessons in Scientific Cookery.
Frying is cooking in hot fat deep enough to entirely cover the articles to be cooked. When food is properly fried the fat is hot enough to instantly sear the outer surface and thus prevent it soaking into the food. All food to be fried should be thoroughly dried; if water should drop into the hot fat it would cause the fat to boil over, and there is danger of it taking fire and causing great trouble. Food that does not contain sufficient albumen to form a coating on the outside as soon as immersed into the hot fat should be rolled in crumbs, then in egg and again in crumbs to form a grease-proof covering. A frying basket, or a wire basket with a long handle, is very convenient for frying purposes. In many cook books we read, "heat the fat smoking hot." That depends entirely upon the kind of fat you are using; lard will smoke at a much lower temperature than oil. When fat smokes it loses some of its browning properties; never let fat heat without putting a small piece of raw potato into it. As soon as the potato begins to brown drop in a fresh piece of potato; if it browns in one minute the fat is hot enough to fry potatoes and dough mixtures. For such food as we roll in bread crumbs and egg the fat should be hot enough to brown a bit of bread in forty seconds.
The best fat for frying purposes is a mixture of suet and oil, as both these fats can be heated to a much higher temperature without smoking than lard, and are more healthful. Olive oil is the purest fat for frying, but is too expensive for general use.
For frying the same fat can be used several times if properly cared for. The most delicate croquettes can be fried in the same fat with fish and not be marred in flavor. When frying several different kinds of food at the same time, begin with potatoes, then dough mixtures and lastly articles rolled in crumbs.
When finished with the fat drop three or four slices of raw potato into it; cool slightly, and strain through a fine strainer or a strainer cloth.
Pare the potatoes and cut into strips one-half inch in thickness; let stand in cold water one hour; heat the fat hot enough to brown a thin slice of potato in one minute; wipe the potatoes; put into the frying basket and lower into the hot fat; do not put a large quantity of potatoes in at one time, as they will lower the temperature of the fat and the potatoes will be soggy and greasy. When the potatoes are nicely browned lift from the fat and shake free from grease; turn onto a piece of cheese cloth to absorb the fat; dust lightly with salt, and serve immediately. French fried potatoes should be crisp and mealy. If they stand they become soggy.
Pare the potatoes and slice very thin; let stand in cold water two or three hours; wipe dry; fry in fat hot enough to brown in one minute: when nicely browned remove the basket and shake well; turn chips onto cheese cloth or soft paper; dust well with salt.
 
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