Frying oils withstand high heat because they have high smoke points, while cold-pressed oils are made to be used without heating, in their raw form, because of their lower smoke points. This difference comes from how the oil is processed and how well its compounds tolerate heat.
What Does the Smoke Point Determine?
The smoke point is the temperature at which an oil starts to smoke and deteriorate; when heated above this point, the oil leaves a bitter taste and can produce harmful compounds while releasing heavy smoke and odor in the kitchen. Frying oils such as refined sunflower and canola oils have smoke points above 200°C / 392°F, which makes them suitable for frying and high-heat cooking. Unprocessed oils such as cold-pressed olive and flaxseed oils have much lower smoke points, generally in the 160–190°C / 320–375°F range. When heated, these oils reach their smoke points sooner and their delicate aromas deteriorate; that is why they are reserved for salad dressing, hummus, or drizzling over a cooked dish at serving time.
Why Is Cold-Pressed Oil Unsuitable for Frying?
Cold pressing is designed to preserve the oil’s aroma compounds and nutrients; the oil is pressed without being exposed to heat. Using this oil for frying both damages these delicate compounds with heat and wastes money, because cold-pressed oils are generally considerably more expensive than refined oils.
Which Oil Should You Use for Which Recipe?
Choose a refined oil with a high smoke point for processes such as frying, sautéing, and roasting at high heat; for salad dressing, appetizers, and sautés exposed to little heat, let the aroma of cold-pressed oil stand out. You can also combine the two types: cook the food in frying oil and drizzle a few drops of cold-pressed olive oil over it at serving time so the strengths of the two oils can be used together.
Can You Reuse Frying Oil More Than Once?
Oil used for frying can be reused a few more times, but its smoke point drops a little each time; oil that has turned cloudy, foams, or smells burnt can no longer be safely reused. Cold-pressed oils are already not made for reheating, so they are completely outside this discussion—their shelf life is measured in a few months after opening, when stored in a cool, dark place.
Why Do Package Color and Bottle Material Matter?
Cold-pressed oils are usually sold in dark glass bottles because light damages the oil’s delicate compounds and shortens its shelf life. Oil sold in a clear plastic bottle may have been exposed to light on a store shelf for weeks, or even months; when possible, choose products in dark glass bottles and keep an opened bottle in a cupboard, in a cool place away from direct sunlight.