PURPOSE: To prevent the eluation and diffusion of a coloring matter from colored agar-agar, by preparing a colored agar-agar gel through the use of sodium caseinate and a lactone, followed by adsorbing the coloring matter dissolved in the agar-agar with casein.

CONSTITUTION: Agar-agar is blended with sodium caseinate, a lactone, preferably gluconodeltalactone, as an acid forming agent, and a proper amount of sugar to give a blend, to which water is added and stirred fully so that the blend is dissolved. A synthetic coloring matter is added to the resulting solution, which is heated to 90W 95°C under stirring and allowed to stand and cooled.