Metastable states in a food extrusion cooker

Abstract

An extrusion cooking process for the manufacture of expanded wheat flour products was found to exhibit two states in which the system could come to equilibrium for the same settings of the independent process variables. Examination of the degree of fill in the sections of the screw and observations of the dependent process variables such as torque, pressures and mass temperatures enabled an explanation of the metastable states to be proposed related to moisture movement within the screw system. Certain design features of the screw system are proposed to eliminate this form of instability.