A General Model for Expansion of Extruded Products

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Abstract
The expansions (cross‐sectional, longitudinal and volumetric) of corn extrudates made with a single‐screw extruder were studied. Longitudinal and Volumetric Expansion Indices were developed to characterize the product's specific length and volume. To explain the results, it was postulated that increased stored energy in the elastic starch melt occurring with higher shear strains favored radial expansion at the expense of longitudinal expansion. An inverse relationship between radial and longitudinal expansions was confirmed. A general expansion model involving dough moisture, melt temperature, and die and screw shear strains described all three expansions and characterized the thermally induced expansions with associated energies of activation.