Fats and Oils: Effects of Heat

Fats and oils are not much changed by heating to moderate temperatures; they do not become ‘cooked’ in the same way as proteins or carbohydrates. (Butter is changed by heating because it includes water, which boils away, and protein, which cooks.) If an oil is heated excessively it begins to break down; a sign of this is that it gives off smoke. Soya oil, one of the most heatproof oils, has a ‘smoke point’ of 256 °C (492 °F). It does not actually catch fire until it reaches about 350 °C (662 °F). If flour particles fall off food which is being deep fried and float in the oil, they lower the smoke point considerably.