Since microwave energy does not interact well with ice, thermal runaway might occur due to the localized melting in the frozen zone and this can be a problem during microwave assisted freeze drying. Also, in industrial applications plasma discharge/arcing might occur which result in the poor product quality and may also eventually lead to the
destruction of the food products. The chance of plasma occurring is related to the pressure in the chamber. To minimize the probability of arcing, it was suggested to operate at low microwave power during low
pressure operations. Also, cycling the pressure from low to moderate might also control the plasmadischarge. Thus the chamber pressure becomes a suitable control parameter to control and avoid plasma discharge. In general, microwave freeze drying is a complex control problem (Zhang et al., 2006).