Rheological properties of beds of raisins

The rheological properties of beds of Sun-dried Sultana and Corinth raisins equilibrated to various moisture levels were investigated. Raisin beds of fixed bulk density at various configurations were compressed in a cylindrical rest cell, and the apparent modulus and the two constants of an empirical model were estimated from the linearized stress/strain and relaxation curves. Beds of black Corinth raisins were more elastic than Sultana (seedless) raisins at moistures lower than 18%, bur both types of raisins showed similar rheological behavior at higher moistures. The unrelaxed stress of all beds, after 10 min of relaxation, was about 25% of the initial stress. Beds of randomly mixed raisins of different moisture content appeared to be more elastic when the proportion of the moist raisins was increased. The apparent modulus of columns of raisins decreased as the number of raisins per column and the number of adjoining rows were increased.