It is shown that when in the spray freeze drying process stratified packed beds are employed where the smallest in size particles are located near the surface of the lower heating plate while the largest particles are occupying the upper part of the stratified packed bed whose outermost surface is in contact with the atmosphere of the drying chamber of the freeze dryer, the duration times of the primary and secondary drying stages can be substantially reduced when compared with those required by a spray freeze drying process which uses a single packed bed formed by particles all having the same particle size and the total amount of solids in the packed bed is the same as that in the stratified packed bed. (C) 2015 Elsevier Ltd. All rights reserved.