Cooking Oil Smoke Points

Smoke point is the temperature at which a fat begins to visibly break down rather than simply heat up. Heat splits the fat molecule into free fatty acids and glycerol; the glycerol portion then decomposes further into acrolein, the pungent, irritating compound that makes up the bulk of the visible smoke. Once an oil starts producing acrolein, its flavor degrades and it's no longer suited to the cooking task at hand.

An oil's existing free fatty acid content, not just its fat type, strongly affects how soon this happens -- oils already carrying more free fatty acids smoke at lower temperatures because they need less additional heat to reach the breakdown point.

Refining is the main reason smoke point varies so much between oils that come from similar source material. Unrefined, cold-pressed oils like extra virgin olive oil retain plant particulates, proteins, and free fatty acids that burn off at relatively low temperatures, which is why EVOO's smoke point sits well below many refined oils.

Refining processes -- filtering, bleaching, and deodorizing -- strip out those compounds, which is why a refined oil made from the same source generally tolerates higher heat than its unrefined counterpart. Ghee follows the same logic in reverse: it starts as butter but has its milk solids removed, and removing those solids is precisely what raises its smoke point well above that of whole butter.