A method of preparing particles of a substance, for example selected from a flavour, fragrance, pigment, dye, biologically active compound or a plastics material, comprises contacting the substance or a formulation (which may include the substance in conjunction with a second solvent) with a first solvent which comprises a C1-C4 hydrofluorocarbon, especially tetrafluoroethane, and subjecting the resultant mixture to a separation process, for example, by allowing the mixture to be sprayed as a mist (14) from a high pressure environment in a first vessel (2) to a low pressure environment in a second vessel (8), thereby to cause separation of at least some of the substance from the first solvent and the formation of fine particles (20) of the substance.