In my previous column (Cereal Foods World, July-August, 2006), I discussed the use of steam preconditioners in front of cooking extruders. In this column, I will discuss a related method of adding thermal energy to extruders—steam injection. Although widely practiced, it is not as widely used as steam preconditioners. Unlike preconditioning, virtually nothing has been written about steam injection. The only reference that I am aware of that discusses this in any detail is Robert Miller’s notes on heat transfer in the AACC International course on extrusion. Like preconditioning, steam injection offers the opportunity of significantly increased extruder capacity, and as far as I can tell, it gets around the problem of reduced heat transfer area per unit capacity that hampers the scale up of heat transfer through the extruder’s barrel.