This paper proposes a direct and continuous method to measure convective heat flux (phi(c)) during batch deep-frying, based on signal reconstruction techniques applied to local oil temperature measurements. The method was applied on the assessment of convective heat transfer of 1.5 mm thick cassava slices, for various conditions of stirring and oil temperature (140-160 degreesC), and validated independently from mass balance results on slices. Finally, frequency information on the dynamic of convective heat transfer was used to propose a mechanistic interpretation of internal coupled heat and mass transfer identified within thin materials. Three regimes of coupling were identified during the first minute of frying and were respectively related to (i) an unstable superficial vaporization with phi(c) values higher than 100 kW m(-2), (ii) a regular internal vaporization with phi(c) values oscillating between 15 and 35 kWm(-2) controlled by liquid water transport from core, (iii) a decreasing vaporization rate subsequent to the rapid vanishing of the saturated region.