Research on microwave vacuum drying for instant Ersi

Instant Ersi is a popular and delicious snack in Yunnan, China. Microwave-vacuum drying (MVD) method of Ersi was studied, and compared with hot-air drying (HAD). The MVD under 1.5kW microwave power and at pressure of 65kPa can significantly reduce the drying time of Ersi by about 99% compared with HAD. Brightness of Ersi using MVD was slightly higher than that of HAD. The apparent size of dried Ersi in MVD was 0.5mm larger than by HAD. From scanning electron micrographs, the microwave-vacuum dried Ersi had more open structure and pores than the hot-air dried ones. Moreover, the maximum pore size (55.4μm) by MVD was about two times of that (24.5μm) of HAD. From rehydration test, the rehydration time of MVD was less than 3-4 min by HAD.