The way McDonalds makes its fries isn't a secret. They let Food Network film part of a documentary on fried food in one of their french fry factories, and showed the entire process from potato to frozen product ready to ship. It was basically cleaning and sizing (large potatoes cut in half), shot through pipes by water pressure with a grate on the end of the pipe that cuts the potato into fries, steamed to make the inside fluffy, then fried twice at two temperatures.