Rheological characterisation of cake batters generated by planetary mixing: Elastic versus viscous effects

Studies of cake batter rheology have focused on viscous behaviour. We demonstrate that elastic effects dominate at the shear rates used in commercial mixers. The development of batter structure was investigated for two flour types using two bench-scale planetary mixers with known shear rate profiles (Kenwood-KM250, maximum 100 s −1; Hobart-N50, 500 s −1). These wet foams (air volume fraction 0.39–0.45) showed shear-thinning behaviour at low shear rates (0.1–10 s −1), with apparent viscosity dependent on air volume fraction. Simple shear thinning behaviour ceased, for foams, above 10–20 s −1: for slurries (air volume fraction, 0.11–0.15) the limit approached 100 s −1. Elastic effects, predominantly arising from the bubble phase, therefore dominate cake batter behaviour at the shear rates experienced in commercial mixers. Filament thinning extensional rheometry confirmed the VE behaviour of batters. These results indicate that visco-elastic analyses are likely to be the most appropriate probe of microstructure in cake batters.