For gel-like or solid food products which contain suspended particles, heating or cooling processes cannot always achieve convection heat transfer. The authors have established a basic measuring method for thermal diffusivity a, which is important for heat processing of this unsteady zone, by the Hot-wire method. With this measuring method, a calibration curve is drawn between tau(1/2) (the half time for Delta T required to achieve a quasi-steady condition) and the themal diffusivity a. Separately, a "Time-Temp. difference" curve is created using developmental measuring equipment for a sample with unknown thermal diffusivity a. This curve is used to calculate tau(1/2). From the above calibration curve, the thermal diffusivity a of the unknown sample can be obtained. The non-dimensional effective thermal diffusivity obtained by this method matchs closely with values obtained by previous researchers.