Apple quality preservation with the use of intermittent drying process

Abstract

During the fruit drying, the processes of heat transfer and mass transfer occur simultaneously in the dried product. To preserve the fresh fruit quality or even to improve some of its nutrition characteristics, discontinuous heat input is used in the proposed intermittent drying process. The pause, in the heat supply, provides enough time for moisture diffusion within the material. Existing food drying theory can not be sufficient for specifying the intermittent drying regime. In the industrial environment, in which this research is conducted, true intermittent drying process is searched through tests at relevant drying conditions. Intermittent drying process is studied by tempering apple rings during air drying. The investigation was performed using a three-level industrial type dryer. Multi-thermal zone convective drying process is applied, with different intermittent regimes, on three identical continuous flow dryers. The influence of air state (temperatures 35-85oC, velocities 2-5 m/s) and drying intensity (5-10 h per cycle) on dried product quality is evaluated through field work tests at three simultaneously operating plants. Correct drying conditions are reached.