Abstract: The present invention is a system and method for reducing the size of a hygroscopic material while simultaneously drying the material at a relatively low temperature to a predetermined value during the reduction process. The present invention utilizes a preconditioning make-up air system to significantly dehumidify the make-up air to values in the range of 0.02 grains per pound of dry air while limiting the temperature of the make-up air exiting the preconditioning make-up air system to below a predetermined critical value. While not limited in its application to any one particular hygroscopic material, the present invention is particularly adapted to uses where the product is a temperature-sensitive, water adsorbing material such as sodium sesquicarbonate or trona ore.