STRAIN-HARDENING AND DOUGH GAS CELL-WALL FAILURE IN BIAXIAL EXTENSION

Dough theological properties were measured in biaxial extension using a modified Chopin Alveograph under conditions close to those of baking expansion. The resulting stress-strain curves showed power-law strain hardening, indicating an increase in stiffness with increasing inflation. This strain hardening was shown to be critical in determining the limit of bubble expansion, both in the Alveograph and in baking. A criterion for gas cell-wall instability and failure has been derived, which takes into account the strain and strain-rate hardening Properties of dough during large extensional deformation. Differences in bubble stability were observed between different wheat cultivars at low rates of inflation close to those of baking expansion, but these differences disappeared at the higher rates normally associated with theological testing.