Abstract: An improved method of producing semi-refined kappa carrageenan is provided having processing steps including: (a) pre-rinsing carrageenan containing seaweed; (b) cooking the seaweed in a cooking tank containing an aqueous solution of KOH to cause desulfation at the 6-position of the galactose units of the carrageenan, to create recurring 3,6 anhydrous galactose polymers by dehydration and reorientation; (c) washing the seaweed in a neutralizing bath; (d) rinsing the seaweed in water; and, (e) drying and chopping the seaweed, the improvement being monitoring the reaction progress of the desulfation, dehydration and reorientation by continuously measuring oxidation-reduction potential of the aqueous KOH solution and, upon the occurrence of substantial reaction equilibrium of the reorientation, as indicated when the oxidation-reduction potential has reached a pre-determined constant value, stopping the reaction by removal of the seaweed from the aqueous KOH solution.