Apparatus and methods for food production including a food preconditioner (228) operable to heat and partially pre-cook food ingredients, and a twin screw extruder (20) operable to further cook the preconditioned ingredients to create final food products. The extruder (20) includes a pair of hollow core extrusion screws (50, 52, 124, 126, 190) having elongated hollow core shafts (54, 128, 130, 192) equipped with helical fighting (56, 132, 134, 194) along the lengths thereof. The fighting (132, 134, 194) is also of hollow construction which communicates with the hollow core shafts (54, 128, 130, 192). The flighting (56, 132, 134, 194) also includes forward, reverse pitch sections (64, 162, 216). The extrusion screws (50, 52, 124, 126, 190) are designed to impart high levels of thermal energy into materials being processed in the extruders (20), without adding additional moisture.