Process Optimisation and Minimal Processing of Foods

Step changes in air temperature(±20oC) or velocity (±0.8 and ±1.5m/s) were introduced in an air drying process, in relation to standard drying conditions of 70oC and 1.5m/s of air temperature and velocity, respectively. Compared to the standard, the variable conditions caused a clear difference of the moisture content of the dried material and the drying curves deviated significantly after the step change. Experiments carried out with constant and variable conditions showed a larger influence of air temperature than air flow velocity on the drying curves or on the time required to obtain specific levels of water content (35, 17 or 12%). The influence of constant or variable air velocity cannot be neglected, although its importance decreases with processing time.