Many of us love fried foods. Just scan the many menus of popular fast food restaurants as proof. For those who advocate a healthy lifestyle, frying does not need to be banned from the kitchen repertoire, but it does beg the question “How can frying foods in our own home be elevated to a cooking process that will be associated with wellness and longevity”?
Olive oil is a superior health food when compared to the commonly used vegetable oils for frying, but all oils are dynamic in nature. They are constantly changing their chemical constituents – both during storage and the cooking process. With properly stored olive oil, such as in a fusti topped with inert gas, those changes can remain undetectable to human taste for quite a while. After a bottle has been opened, however, loss of flavor and healthy components happens over a matter of weeks.
The process of frying is different because heat accelerates chemical changes. All oils will smoke when heated to a specific temperature (smoke point) and olive oil is no different. In particular, the smoke point of oil varies with its quality. High quality extra virgin olive oils (with low free fatty acids) have a high smoke point. They are an excellent choice, albeit an expensive one. Mass produced, low quality olive oils have a much lower smoke point.
It is estimated that extra virgin olive oil smokes roughly between 400 and 365ºF (204 and 185ºC) depending on its free fatty acid content. Here is what the International Olive Oil Council (IOOC) has to say about frying food with olive oil:
When heated, olive oil is the most stable fat, which means it stands up well to high frying temperatures. Its high smoke point (410ºF or 210ºC) is well above the ideal temperature for frying food (356ºF or 180ºC). The digestibility of olive oil is not affected when it is heated, even when it is re-used several times for frying.
Regardless of which type of oil is used, cooks should avoid heating above the oils’ smoke point. As long as the oil does not reach its smoke point, no harmful by-products are created. The flavors and the healthy qualities of the oil are degraded, however.
Extra virgin olive oil is the most beneficial oil because of the high quantities of monounsaturated fats and polyphenols. There are three key areas of chemical change that occur when oil is heated. First, oleic acid, the monounsaturated fatty acid that is a key to olive oil’s antioxidant qualities because of its more stable chemical makeup (which makes it more difficult for oxygen radicals to interact with it), is diminished when heated beyond 200-250 degrees F°. Second, studies have shown that exposure to heat as low as 320 degrees F° can substantially damage the phenols in olive oil. Third, valuable amounts of Vitamin E are lost during a cooking process that involves high heat.
But while it is clear that chemical changes are exaggerated when an oil is heated, the breakdown of an oil is not necessarily a completely detrimental process. As cooking oil begins to breakdown with heat, the products produced are able to flow past the water barrier on the food and produce surface browning and complete cooking. Old time cooks added a small amount of previously used oil (partially broken down chemicals) to the new oil for better frying. Without any breakdown, meats or vegetables will not produce a pleasing brown surface or a center that is thoroughly cooked. The oil may lose some of its beneficial quality, but olive oil imparts a special flavor to the foods being prepared which simple vegetable oils can’t match. It becomes a trade-off for flavor that may occasionally be worth it.
Bottom line, olive oil is a superior health choice over commonly used vegetable oils. Not only is olive oil an excellent choice for light to medium frying, but it is unsurpassed to drizzle over a salad, use in marinades or in sauces that are mildly heated. In our kitchen, the advantage of using olive oil for healthy living surpasses the use of the vegetable oils for slow and medium heat frying.
For those who are curious about oils and the frying process in general please read Russ Parsons' excellent first chapter in “How To Read a French Fry”.