Handling Fats Finally, a word about oil storage and cooking. As oils age, they begin a natural process of breaking down. Over time, breakdown causes oil to turn rancid and flavor changes occur. But even before a detectable flavor change, oil breakdown results in free radical formation and some other chemicals suspected of initiating cancer form. This occurs more rapidly when oil, especially vegetable oil, has been exposed to oxygen or heat.
Antioxidants help neutralize free radicals, but proper handling of fats is also important.
Keep Oils Fresh Don't reuse an oil that has been heated. Start with fresh oil each time. Buy oil in smaller amounts, only what you need to last 2 to 3 months. Keep oils at a cool temperature, with the top securely tightened. Do not eat stale processed foods that have oils or fat as ingredients.