Demystifying Oil

Buying cooking oil used to be an easy task. You walked into the grocery store, went down the baking aisle, and pulled a bottle from the shelf. There were no options; there was no confusion.

Today, entire aisles are devoted to cooking oil. Oil can come from just about anything, such as avocados, almonds, and soybeans. And to add to the confusion, you can get oil flavored with anything from chili peppers to rosemary to lemon.

How do you know which oil is best for your sizzling vegetable stir-fry, perfect pumpkin muffins, or savory balsamic salad dressing? Getting to know a little bit about oil will help you decide which oil is right for your cooking project.

Oil From Just About Anything

Oil can be made from a variety of sources, such as:

• Seeds: safflower, sesame, sunflower, seeds from canola plant
• Nuts: almond, walnut
• Grains: corn
• Beans: peanut, soy
• Fruits: avocado, olive, coconut

The first step in processing is to remove the oil from the seed, nut, grain, bean, or fruit. The extraction process can be chemical or mechanical. When done chemically, the oil source is soaked in a petroleum compound, usually hexane. The oil then requires further refining to remove this toxic solvent. This method is efficient, provides a high yield, and is more common than mechanical extraction.

Mechanical pressing, also called expeller-pressed, uses no chemicals. The oil is derived from its source by squeezing it in a mechanical press. The process can raise the temperature of the oil. Cold pressed means that no additional external heat is added during the processing. Oil purists believe that unrefined, cold pressed oil retains the most flavor, aroma, color, and nutrients.

Understanding Oil's Structure

In order to know which oil to choose, it is important to understand a little bit about the chemistry of oil. Oil is made up of fatty acids. A fatty acid is a chain of carbon atoms. Every carbon on the chain has places that hydrogen atoms can fill. If each carbon on the chain has all the available slots filled with hydrogen atoms, it is a saturated fatty acid (SFA).

If the fatty acid chain is not holding all the hydrogen that it can, it is considered unsaturated. When there is 1 point of unsaturation, the fatty acid is considered monounsaturated (MUFA). If there are 2 or more points of unsaturation, the fatty acid is polyunsaturated (PUFA). Specially modified margarine-like fatty acids are known as trans fats.

Saturated fats raise total blood cholesterol, as well as LDL (“bad”) cholesterol. However, they also may raise levels of HDL (“good”) cholesterol. In contrast, certain polyunsaturated fats may improve most or all aspects of cholesterol profile. Trans fats, on the other hand, worsen most aspects of cholesterol profile and should be avoided.

Properties of Oil

The more unsaturated an oil is, the more oxidation may occur. Oxidation causes rancidity, which produces an off-flavor in the oil. Rancidity can also produce a bad smell. So, if the oil doesn't smell right, don't use it.

Oil should be used within 6-12 months after opening. To help preserve the flavor and quality, store your unopened oil in a cool, dark cupboard. After the oil is opened, you can keep it in the refrigerator. Olive oil, however, will thicken in the refrigerator—so only keep it in there if you are using it infrequently.

Smoke Point Determines Use

If you are cooking with oil and it begins to smoke, you have reached its smoke point. At the smoke point, the oil begins to emit unpleasant odors and impart unsavory flavors to your meal. Watch out for the smoke point signs. Getting to it means you are getting close to the flash point, which is when the oil can erupt into flames.

Knowing the smoke point is important when determining which oil you are going to use. (See examples in the table below.) Oil with a low smoke point is good for salad dressings, wine sauces, and seasoning, while the higher smoke point oils should be used for sautéing, baking, or frying.

The following table lists the percentage of fatty acid and smoke point of different types of oils:

The Goodness of Oil

Oil contains essential fatty acids, which your body needs to survive but can't make and therefore must be obtained through food. Oil is a source of vitamin E as well. In addition, oil is crucial for absorbing and transporting the fat-soluble vitamins A, D, E, and K throughout the body.

No matter which oil you choose and no matter what you choose it for, remember to use it in moderation. And in accordance with the American Heart Association's recommendations, opt for an oil high in monounsaturated or polyunsaturated fatty acids.

Revision Information

• Reviewer: EBSCO Medical Review BoardMichael Woods, MD, FAAP
• Review Date: 01/2018
• Update Date: 01/30/2014