Extrusion processing with supercritical fluids

Abstract

A supercritical fluid such as CO.sub.2 is injected under pressure into a fully cooked dough in an extruder. The dough is prepared and after being preconditioning with water and steam, is supplied to an extruder/cooker where it is subjected to high cooking temperatures, which may be on the order of 120.degree. C. The cooked dough is conveyed through an optional steam vent section and is cooled to a temperature of usually less than 100.degree. C. to prevent puffing of the extruded product by the conversion of water to steam. Supercritical CO.sub.2 is injected into the cooked and cooled dough, and under the pressure conditions existing in the extruder, the CO.sub.2 dissolves into the water phase of the dough. Since the conditions within the extruder are either subcritical or near-critical, various flavors, colorants, or other materials soluble in and carried by the supercritical CO.sub.2 are deposited and mixed into the dough before exiting the extruder. The dissolved CO.sub.2 then expands the product after exiting the die at the outlet of the extruder, resulting in a product with many regularly-shaped, unconnected pores and a smooth outer skin. Part of the injected CO.sub.2 can be vented off before the die to control the expansion of the extrudate.

Dependencies are inferred from the claim text.