Rank and Midmore (2006) classified the refining methods of stevioside into solvent partition extraction mainly methanol or water extraction and solvent partition extraction, incorporating mainly in situ precipitation with calcium hydroxide–carbon dioxide to remove impurities, similar to the purification process in the sugar industry. They also reported different methods of purification, such as adsorption, chromatography, ion-exchange, plasmid gel or adsorption by activated carbon.