A redox analysis technique built on reactions with iodine/iodide: strong reducing agents are titrated with iodine, while strong oxidizing agents liberate iodine from iodide. A standard thiosulfate solution titrates the liberated iodine, with starch solution as the indicator. Food laboratories routinely apply it to analyses such as peroxide values in fats and oils, where it quantifies the oxidation that drives rancidity. The sharp starch-iodine colour change makes endpoints easy to read. Careful standardization of the thiosulfate titrant keeps results accurate.