Pure vegetable oils are common in cooking and baking. Their light, neutral flavor makes them highly versatile and the unsaturated fats in vegetable oil have been embraced for their potential health benefits. Unfortunately, unsaturated fats are more prone to spoiling and turning rancid than saturated fats are. A few simple tips can help prolong the life of your cooking oil, especially if it is to be saved and reused.
Preventing Rancidity in Fresh Oil
Store cooking oils out of direct light, especially direct sunlight. Light can break down the oil molecules, causing a deterioration in flavor and eventually distinctly rancid tones. This is why high grades of olive oil are commonly sold in cans or tinted bottles.
Find a cool place to store your cooking oils. It may be convenient to have them directly over the stove, but the heat from cooking will shorten their shelf life. A low cupboard near the stove is a better choice, because heat rises and a place near the floor is usually cooler.
Replace the cap on your oil bottle after every use, as oxygen will also break down oils over time. Don't shake or agitate the oil if you can help it, because this introduces extra oxygen. Narrow bottles are better for oil than wide bottles, because they expose a smaller surface area to the air.
Preventing Rancidity in Used Oil
Reduce your use of salt in fried foods, if you wish to reuse the oil a second time. Salt breaks down the chemical bonds in the oil molecules, and speeds deterioration.
Avoid using liquids or liquid seasonings in frying oil, because liquids also break down the oil molecules. Liquid seasonings also tend to contain salt, which increases the damage. Foods tend to release their natural juices into the cooking fat when they are approaching doneness, so avoid overcooking.
Filter used oil through several layers of cheesecloth or paper towel after use. Prop a funnel into the mouth of a glass jar or other storage container, and line the funnel with your filtering material. Pour the oil through the filter into the jar, while it is still warm. Date the jar and store it in a cool, dark place for reuse.
Never cook with oil that has turned rancid or developed off-odors. When polyunsaturated fats become rancid, they contain molecules called lipid hydroperoxides. These fat compounds have been identified as damaging to DNA.