Pulsed microwave-vacuum drying of food materials

Microwave drying of food materials has been investigated over several years as a potential means for reducing the total drying time. However, some qua lity loss almost always accompanied when foods were dried completely using microwaves due to nonuniform temperature and moisture distribution. Some st rategies used to improve dried product quality include combination of micro wave and conventional hot air drying, pulsed or intermittent drying, and mi crowave-vacuum drying. Combination of pulsing and vacuum drying is a useful technique to maximize energy use efficiency and product quality especially for temperature sensitive products such as fruits. Some results of pulsed, microwave-vacuum drying of cranberries are presented. Pulsed drying is mor e energy efficient than continuous drying. In pulsed drying, the longer the pulsing ratio (i.e. longer power-off time in relation to power-on time) wa s more energy efficient. The quality of pulse-dried product was also genera lly better than that of continuous-dried product. The cycle power-on time a nd pulsing ratio should be carefully selected to obtain maximize the benefi ts of pulsed, microwave vacuum drying.