As far as KFC, I think they just sweep up at night and use what they get in the next day's chicken...
McDonald's® Famous French Fries
French Fry Cutter
(or patience for cutting potatoes)
2 large Idaho russett potatoes
1/4 cup sugar
2 Tablespoons corn syrup
1½-2 cups hot water
6 cups Crisco® shortening
1/4 cup beef lard (or save the fat from previously cooked burgers)
Preparing your french fries
Peel the potatoes. In a large mixing bowl, combine sugar, corn syrup, and hot water. Make sure the sugar is dissolved. Using a french fry slicer, cut the peeled potatoes into shoestrings. The potatoes should be 1/4" x 1/4" in thickness, and about 4" to 6" long. (You can do this with a knife, but it is alot of work)
Place the shoestringed potatoes into the bowl of sugar-water, and refrigerate. Let them soak about 30 minutes.
While they're soaking, pack the shortening into the deep fryer. Crank up the temperature to "full". The shortening has to pre-heat for a very long time. It will eventually liquify. After it has liquified and is at least 375°, drain the potatoes and dump them into the fryer. (be careful, it will be ferocious)
After 1 to 1½ minutes, remove the potatoes and place them on a paper towel lined plate. Let them cool 8 to 10 minutes in the refrigerator.
While they're cooling, add the lard or beef drippings to the hot Crisco®. Again, crank the temperature to full. Stir in the lard as it melts into the oil. It will blend in.
After the deep fryer is reheated to 375°-400°, add the potatoes and deep fry again. This time for 5-7 minutes until golden brown. Remove and place in a large bowl.
Sprinkle generously with salt, then "toss" the fries to mix the salt evenly. ( I suggest about 1 teaspoon of salt, maybe slightly more)
Serve hot, serve immediately, and enjoy! Depending upon the size of the potatoes, this recipe make about 2 medium sized fries.
Note¹ If you want more fries, double the recipe---but DON'T double the cooking oil. Just cook them in shifts, adding about 1/4 cup more Crisco® and 1 tablespoon lard for the second batch.
Note² If cooking for a minute or so, removing, and returning the fries to the oil seems like a pain in the ass, that's because it is. But it is an important "blanching" step required for that great taste.
Note³ For an easier clone of McDonald's french fries, you can use the frozen, pre-cut Ore-Ida® shoestring potatoes. Just cook them in the same combo of Crisco® and lard, skipping the "blanching" process. Cook them while still frozen for 6-10 minutes (depending upon the amount) until golden brown. They're good, but not nearly as accurate in taste and texture as the fresh recipe.