The bioavailability of a pharmaceutical depends on the crystal structure of a polymorphic active ingredient or excipient. By changing the process parameters of the PGSS (particles from Gas Saturated Solutions) process i.e. thermodynamic conditions of the solidification process it is possible to vary the crystal modification of polymorphic products. In a series of PGSS experiments microparticles of the polymorphic excipient tristearin as well as of mixtures of tristearin and the emulsifier sorbitan monolaurate were successfully produced. Pre-expansion pressure was varied between 6 and 22 MPa. The effects of process dependent parameters on the crystallization were investigated via scanning electron microscopy, differential scanning calorimetry and X-ray powder diffraction. Metastable alpha-forms of tristearin were found immediately after the processing for all experiments. Further it was found that it is possible to shift the conversion rate of polymorphic transitions in the product either by varying the process parameters or by adding the emulsifier.