NMRI studies of the free drainage of egg white and meringue mixture froths

The free drainage of egg white (EW) and EW/icing sugar froths is studied by measuring liquid hold-up (volume fraction) profiles by nuclear magnetic resonance imaging. The profiles are corrected for spin–spin and spin–lattice relaxation time constant effects to make the results as quantitative as possible. It is found that the addition of sodium dodecyl sulphate (SDS), which is commonly used in the baking industry to improve the ‘whipability’, actually enhances drainage rate because the bubble size is increased and the surface viscosity is diminished. The addition of SDS to EW/icing sugar mixture has no tangible effect upon drainage rate. EW has a bulk rheology that is most shear-thinning that prevents existing models of foam drainage, where the interstitial fluid is assumed to exhibit Newtonian rheology, from being implemented. A hindered bubble rise model is adopted to estimate the liquid drainage rate from EW froth.