AbstractBueche's theory of the mechanical degradation of polymers in shear is applied to try to account for the changes in flour proteins following high‐speed mixing of doughs. Because of the high viscosity of dough (∼ 108poise), shear strain rates on the order of 102sec−1, which are encountered in standard dough mixers, are sufficient to cause scission of covalent bonds. The limiting amount of protein, extractable after mixing, increased with mixing speed, in agreement with the predicted effect of strain rate on breakdown. Agents which crosslinked protein chains through strong covalent bonds increased the mixing stability of doughs, while those which crosslinked by formation of SS bonds greatly accelerated breakdown, reflecting the more labile nature of the SS bond. Some predictions about the rheclogical effectiveness of different SS bonds follow from the theory. Predicted changes in molecular weight distribution of protein following mixing are in agreement with experimental results obtained by ot