3.1. Effects of air temperature on AFD processThe drying curves are given in Fig. 2. The effect of dryingtemperature is best shown for the measurements of samples,where the difference in drying time is 8 h, comparing dryingat −10 and −5◦C down to final moisture content. It is shown that the drying rate decrease gradually and there is no obvious constant drying rate period. From beginning to about 16 h of the procedure, material temperature rises relatively slowly,and this implies the most water is removed in this period.After the moisture content is reduced below 40% (w.b.), the drying rate becomes more slowly, and this period takes up the most drying time of AFD process. As a result, a higher air temperature should be adopted after the moisture content is below 40% (w.b.) in order to reduce the drying time of AFD process. However, considerable freezing point depression would take place at this moisture content level, easily resulting in ice thawing. Therefore it is difficult to establish an efficient dryingstrategy based on the freeze point of material. In fact, whenthe porous structure of product is formed, little ice thawingwould not lead to obvious quality deterioration. This is why achanged temperature program should be used to reduce thedrying time meanwhile promising a good quality.