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 shownthat the drying rate decrease gradually and there is no obvi-ous constant drying rate period. From beginning to about 16 hof 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.), thedrying rate becomes more slowly, and this period takes upthe most drying time of AFD process. As a result, a higher airtemperature should be adopted after the moisture content isbelow 40% (w.b.) in order to reduce the drying time of AFD pro-cess. However, considerable freezing point depression wouldtake place at this moisture content level, easily resulting in icethawing. 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.