Choosing which culinary oil to keep on hand in your refrigerator really depends upon how you intend to use it in cooking and baking. Are you going to drizzle it over a salad or pasta? To sauté a dish or bake at moderate heat? Does your recipe call for medium to high heat cooking? Or are you going to the oil for a stir-fry?
In essence, each of these four levels of heat, from no-heat to high heat, calls for a different type of oil due to a critical factor called “smoke point.” An oil’s smoke point is the maximum temperature it can be heated before it starts to smoke and discolor, both indications that the oil is being damaged by heat.
When oil begins to smoke, it releases carcinogens into the air and creates free radicals within the oil. These highly reactive molecules can cause cellular damage and over time could lead to disease. Even from a purely culinary standpoint, heating oil beyond its smoke point is a problem, as it will give rise to an off taste and acrid smell in the kitchen.
The temperature of an oil’s smoke point is highly affected by its fatty acid profile, which indicates the oil’s unique proportion of saturated fat, monounsaturated fat, and polyunsaturated fat. Culinary oils with a higher proportion of saturated fats are the most stable to heat, followed by those higher in monounsaturated fats. Oils higher in polyunsaturated fats are the most vulnerable.
However, the smoke point of an oil can also be highly affected by the level of refining an oil is subjected to in its production process after the oil is extracted from its seed, nut, bean, or grain.
Examples include flaxseed oil, extra virgin olive oil, and unrefined walnut and hazelnut oils.
These are largely left alone after extraction, and will typically have a lower smoke point than culinary oils that are refined to become more neutral in flavor, less cloudy, or less prone to oxidation.
Unrefined oils are highly valued for their full-bodied flavor, enticing aroma, deep color, and richer nutrient content. They're perfect for no-heat to low-heat applications.
Examples include canola oil, refined peanut oil, high oleic safflower oil, and refined sesame oil.
Refined oils are actually the better choice for cooking at medium to high temperatures. Ironically, removing the nutrients and phytonutrients from an oil makes it less vulnerable to oxidation, especially at higher temperatures. Even so, it is important to buy only refined oils from companies whose refining process is done without harmful chemicals.
A mini-guide to cooking oils
Cold-pressed nutrient-focused unrefined oils such as flaxseed, wheat germ, hazelnut, and wheat germ oil are very sensitive to heat and should never be used in cooking. Instead, use them as in salad dressing, as a condiment, in smoothies, or instead of butter on bread.
Use unrefined oils (flaxseed oil, extra virgin olive oil, unrefined walnut and hazelnut oils) when preparing dishes that need only low to moderate heat (temperatures below 320°F) such as steaming, light sautéing, and drizzling over cooked vegetables or grains. They’re also suitable for salad dressings and most sauces, and can be used in baking when the oven temperature doesn’t exceed 350°F, as the internal temperature of cookies, cakes, and breads will remain below 320°F.
Use refined oils when oiling baking pans, since they can heat up to higher temperatures than are advisable for unrefined oils.
For cooking at medium to high heat (350°F -425°F) such as stir-frying, sautéing with high heat, popping popcorn, grilling, and high-temperature baking, use only refined oils.
Avoid oils produced with GMO crops
Finally, to avoid oils that may be produced from GMO crops currently allowed for agricultural production in North America, if buying canola, corn, or soy oils, or when perusing products that contain cottonseed oil, be sure to only buy certified organic or look for the Non-GMO Project Verified label.