Rehydration ratio is widely used as a quality evaluation method after drying. In fact, it is a complex process and indicates the chemical and physical changes caused by drying procedures (Feng & Tang, 1998; Lewicki, 1998). The rehydration ratio of carrots dried by microwave or halogen lamp–microwave combination oven was found to be significantly different from that of hot-air dried carrots (p⩽0.05) ( Fig. 7). This can be explained by the high internal pressure produced by microwave heating which can cause structure of carrot slices to expand and puff. It was previously shown that microwave dried carrot slices exhibited higher rehydration ratio than air dried ones ( Lin et al., 1998). A less dense structure had higher capacity to absorb water reconstituted. Lower rehydration values of hot-air dried carrots can be an evidence for product shrinkage caused by severe heating and for prolonged drying resulting in irreversible physical and chemical changes.