0 to 20 u00b0 c and particularly preferably about 10 u00b0 c when crystal precipitation is completed before and or after the filtrate is heat treated the concentrating operation may be performed and the conditions of the concentrating operation are not specifically limited as long as heat deterioration of methionine does not occur and various conditions can be basically employed in view of energy efficiency and corrosion of concentrating facility the temperature of the concentrating operation is preferably from about 50 to 160 u00b0 c and more preferably from about 50 to 140 u00b0 c the concentrating operation and the heat treating operation can also be carried out at the same time and in that case the concentrating operation is performed under the conditions of the heat treating operation it is not preferable in view of energy efficiency and others to perform the concentrating operation under comparatively severe conditions of the heat treating operation it becomes possible to remove impurities and coloring components which are present in the circulating system out of the system while effectively recovering methionine and potassium bicarbonate in the filtrate by treating the partially purged filtrate as described above in the present invention as the material of an.