Untreated fats and oils, both animal and vegetable, are likely to become rancid in storage. Oxidation is promoted by the catalytic action of certain metallic ions such as iron, nickel, manganese, cobalt, chromium, copper, and tin. Minute quantities of these metals are picked up from processing equipment. Adding citric acid to the oil sequesters these trace ions, thereby assisting antioxidants to prevent development of off flavors. Although the oil solubility of citric acid is limited, this can be overcome by first dissolving it in propylene glycol. The antioxidant can be dissolved in the same solvent so that the two can be added in combination.