Pizza is an obvious candidate for 3D printing because it can be printed in distinct layers, so it only requires the print head to extrude one substance at a time. Contractor’s “pizza printer” is still at the conceptual stage, and he will begin building it within two weeks. It works by first “printing” a layer of dough, which is baked at the same time it’s printed, by a heated plate at the bottom of the printer. Then it lays down a tomato base, “which is also stored in a powdered form, and then mixed with water and oil,” says Contractor. Finally, the pizza is topped with the delicious-sounding “protein layer,” which could come from any source, including animals, milk or plants.