Bubbles in breadmaking

The stability of failure in single dough bubble walls is related directly to the extensional strain hardening properties of the dough and that strain hardening plays an important role in the stabilisation of bubble walls during baking., according to recent studies carried out at the School of Food Biosciences at Reading University in the UK.

Baking is about bubbles: the size, distribution, growth and failure of these bubbles during proof and baking has a major impact on the final quality of the bread in terms of both appearance (texture) and final volume.

Scientists at the university are currently evaluating rheological methods to predict breadmaking performance using a modified bubble inflation technique, developed by UK company Stable Micro Systems Ltd.

The D/R Dough Inflation System measures the extensional rheological properties of dough and gluten in biaxial extension under conditions of deformation, strain rate and elevated temperatures relevant to breadmaking.

The latest version of the instrument (TA.XTPlus) has the option of continuously variable speed, allowing tests to be performed at constant strain rates and higher temperatures more relevant to proof and baking conditions.

Because dough is viscoelastic, its rheological properties vary with both strain and strain rate. Therefore it is necessary to separate out the effects of strain and strain rate by keeping one constant whilst varying the other. In the new dough inflation test strain is varied and measured as the bubble inflates, and by continuously changing the speed at which the bubble is inflated, strain rate is kept constant.

Researchers in Reading found that strain hardening measured at 50C and constant strain rate for a number of commercial flours of varying quality using the TA.XTPlus system is shown related to commercial breadmaking performance. Results showed that a strain hardening value of around 1.2 discriminates well between flours of poor to moderate quality and those considered to be good and excellent.