STRAIN-HARDENING OF DOUGH AS A REQUIREMENT FOR GAS RETENTION

Mechanisms that can be responsible for the ability of wheat flour doughs to retain gas are discussed. It is concluded that the relevant types of physical instabilities are Ostwald ripening (disproportionation) and coalescence of gas cells. The extent of Ostwald ripening is probably primarily controlled by surface rheological properties; it certainly affects crumb structure, but it cannot explain the differences in gas retention among doughs from various cereals or various wheat cultivars. It is argued that surface forces only provide a stabilizing mechanism for dough films between gas cells, i. e., against coalescence, for films that are much thinner than the diameter of a starch granule. It is concluded that variation in the potential for gas retention among wheat flour doughs is largely due to variation in bulk rheological properties. We propose a new rheological criterion for the extensibility of dough films between gas cells (and thereby for gas retention) that is based on the strain hardening of the dough in biaxial extension exceeding a specific lower limit. The criterion is translated into measurable parameters. Preliminary experiments on doughs with poor and with satisfactory baking performance illustrate its potential importance.