Shrinkage of apple disks during drying by warm air convection and freeze drying

Volumetric and thickness shrinkage evaluated by direct measurement and n-he ptane displacement were determined during convective and freeze drying of G olden delicious apples. For convective drying, the influence of blanching a nd diameter/thickness ratio of the apple disks used were analysed at differ ent levels of moisture content under constant conditions.- It was found tha t shrinkage of dried samples, both by convection and by freeze-drying, is a nisotropic to a level which depends on sample geometry (ratio diameter/thic kness) used. Blanching did not affect shrinkage results. Based on results obtained a new model to predict bulk density of materials during drying is proposed, showing a better fit to experimental data than p revious models reported in the literature. This model was further used to p redict changes in apple porosity during drying.