In Fig. 3 it is possible to observe howthe freezing begins at the lateral
of the sample and progresses towards the middle of the piece. Freezing
process produces a concentration of liquid phase decreasing the frozen
temperature. As a result, a gradient of water chemical potential appears
promoting a water flux from the middle to the lateral, which heats the
sample in the direction of the water flux. This water flux is promoted
by the production of ice and the consequent concentration of the liquid
phase. These phenomena decrease the water activity of the sample.