ABSTRACT
There are two types of operating variables — independent and dependent. Understanding the character of the variables involved can assist greatly in the operation of or experimentation on extrusion systems. Some extrusion variables require standard laboratory analysis or measurements and descriptions of sizes and shapes of machine components. The need to characterize extrusion ingredients cannot be overemphasized. The ultimate character of the food extrudate is dependent upon the composition of the feed ingredients. Moisture is listed as a separate variable in addition to feed ingredients because it is often controlled separately in the extruder. In some food extruders, the screws and barrels are segmented or built up from a number of pieces attached to a shaft or one another, which gives a significant amount of variability in the geometrical configuration of the extruder. The dye injection procedures are the best available for getting an accurate estimate of residence time in the extruder.
