The smoke point of oil is the temperature at which it stops shimmering and starts to smoke One also calls it burning point. It ranges from relatively low 325°F to very high 520°F for various cooking oils and fat.
If oil smokes, it commonly ruins the taste of foods with a bitter or burned note. That can even trigger smoke detectors. Before reaching the boiling point, cooking fat or oil already smokes much more early.
When Cooking Oil Starts to Smoke
Even if food seems perfectly good, it can have a burnnig taste.
When fat as lard, oil or butter smokes, that shows that it breaks into free fatty acids and glycerol. Like this it puts burning tastes in the food and release free radicals. They are unstable atoms that damage cells.
Smoke of oil signals oxidation, which means that it becomes bad.
Smoke point of fat and oils drops if they at least partially break into free fatty acids and glycerol. The glycerol part breaks down to acrolein, that causes the main smoke from heated fat and oils.
Choosing cooking oil, consider chiefly its smoke point. Each oil type has its chemistary. Some work for salads, others for a perfect steak.
Fry foods happen commonly in 350, 450°F, so best use oil with smoke point above 400°F.
Butter has low smoke point around 325°F and serves for light sautéing or fast searing. But long cook in high heat makes it burn. Add oil to butter in the pan does not help the smoke point.
Its milk particles burn at that temperature.
Polyunsaturated fat in oils as sunflower, corn and soy has many double links that easily break during warming. They commonly have high smoke points, which can cheat, because they are less stable in high heats. Smoke point is not the best measure of oil stability.
For oils with high smoke point, producers apply industrial processes as bleaching, screening and heating to remove impurities. Consequently you receive neutral taste oil with long shelf life and high smoke point. Avocado oil reaches 520°F in refined form, while unrefined version stays around 375°F. Oils as safflower and refined avocado oil work for high heat in the kitchen.
Ghee also works wellfor such cooking.