Disclosed in this application are a method for producing a food material containing cysteinylglycine at a high content, which comprises the step of (a) maintaining a starting food material containing glutathione in a ratio of 1% by weight or more based on the solid content at a temperature of 50 to 120.degree. C. and a pH of 1 to 7 in the presence of water, or (b) treating the food material with a .gamma.-glutamylpeptide hydrolase at a temperature of 15 to 70.degree. C. and a pH of 3 to 9 in the presence of water, whereby a food material rich in cysteinylglycine is allowed to result, as well as a method for producing a food flavor (or savor) enhancer, which comprises the steps of (a) adding a sugar to cysteinylglycine or a food material containing cysteinylglycine in a ratio of 0.5% by weight or more based on the solid content, and (b) heating the resulting mixture at a temperature of 70 to 180.degree. C. for a period of 10 to 180 minutes in the presence of water, whereby a natural food material containing crysteinylglycine at a high content, and therefore, a food savor enhancer rich in cysteinylglycine, can be easily provided.