Cooking oils are extracted from seeds, fruits, vegetables and nuts. The way that oil is extracted has a direct effect on how the oil tastes in your food and the amount of nutrients it has to offer. Using heat to extract the oil produces more of it, but heat can degrade the oil’s flavor and nutritional quality. Using low-heat methods produced higher quality oil, albeit in lesser quantities. Therein lies the dilemma what we will break down further.
Cold pressed oils are crushed in a mechanical press without heat and are prized for their rich flavors, but they can be challenging to cook with. While heat can be generated by the pressing process, most cold pressed oils maintain a temperature of less than 120 degrees Fahrenheit. This is because these oils, especially those with high levels of unsaturated fat, tend to degrade when heated. Cold press oils are better used for salad dressings and marinades and to add flavor and texture by drizzling them over finished dishes; and only for cooking at lower temperatures.
Expeller pressed oils are oils that are mechanically pressed and the temperature is allowed to go higher, resulting in a toasted or nutty flavor. Expeller-pressed oils are typically better suited for cooking because they are more temperature-tolerant, though the “smoke point” at which oils are over-heated varies from oil to oil.
Heat increases the amount of oil that can be extracted from the source. Cold and expeller pressed oils don’t render all of the oil. Some oils are extracted by adding chemical solvents to harvest more oil. The chemicals are then burned off at a higher temperature. The solvents are toxic and the process does what most food processing does–strip important nutrients and flavors from the food.
Unlike Europe, the United States does not require oil manufacturers to identify extraction methods. One easy way to identify refined oils is by the container. Because cold and expeller-pressed oils are heat-sensitive, they will be packaged in cans or dark glass bottles to protect the oils from heat generated by light. Refined oils are usually packaged in clear bottles because they are not affected by heat or light.
A Multi Oil Kitchen
The different heat tolerances of cooking oils are one of the reasons you want to have multiple types of oil in your kitchen. This ensures you’ll likely have the right oil for the right dish. Different oils are best for cooking at different temperatures. For example, avocado, safflower, sunflower and peanut oils have very high smoke points (500 deg F) and are well-suited for stir frying at high temperatures. Olive, coconut, grapeseed and sesame oils smoke at lower temperatures (300 deg F) and are better suited for sauteing. Flavorful oils like olive, walnut and flaxseed oils are recommended for dipping and for dressings.
Other factors can contribute to the suitability of oils for cooking. When oil is mixed with batter and/or salt, the method of storage and the length of time it is being heated can also impact cooking results.