Improved extruders and methods for the extrusion cooking of comestible products such as human foods or animal feeds are provided wherein the products may be produced with very low specific mechanical energy (SME) inputs as compared with conventional processing. The methods preferably involve introduction of very high levels of steam into the extruder barrel (12) during processing, which concomitantly reduces necessary SME inputs required to achieve desired cook and expansion levels in the products. In accordance with the invention, fully-cooked pet foods can be fabricated with SME inputs of up to about 18 kWhr/T, whereas aquatic feeds can be fabricated with SME inputs of up to about 16 kWhr/T. In preferred forms, the extruder (10) includes specially configured, intermeshed extrusion screws (18, 20) and a plurality of obliquely oriented steam inlets (48, 50), and an upstream, dual-shaft preconditioner (90) is used having individual variable frequency drives (98, 100) which allow infinite variablility in the speed and rotational direction of the preconditioner shafts (94, 96).