When oil or butter starts smoking while frying, it's a sign that the cooking temperature is too high. This occurs due to the process of thermal decomposition. Every cooking oil and butter has a specific smoke point, which is the temperature at which it begins to break down and produce visible smoke.
The smoke point is different for each type of oil and fat, but generally, oils with higher levels of unsaturated fats have lower smoke points. When the oil or butter is heated beyond its smoke point, the following reactions take place:
Breaking down of fats: At high temperatures, the heat causes the fats in the oil or butter to break down into their constituent fatty acids. This results in the release of volatile compounds and free radicals.
Formation of acrolein: Acrolein is a pungent and irritating compound that is produced when glycerol (a component of fats) is broken down. It is one of the substances responsible for the visible smoke.
Polymerization: Polymerization is a process where the fatty acids recombine to form larger molecules. This leads to the formation of solid particles in the oil, contributing to the smoke.
Formation of other volatile compounds: Apart from acrolein, other volatile compounds like aldehydes and ketones are also generated, which contribute to the smoke and unpleasant odors.
When you notice the oil or butter smoking, it's essential to lower the heat immediately and remove the pan from the stove if necessary. Cooking at excessively high temperatures not only releases harmful compounds but also affects the taste and quality of the food. It can lead to a burnt and bitter flavor and reduce the nutritional value of the dish.
To avoid oil or butter from smoking while frying, it's best to use oils with high smoke points, such as peanut oil, canola oil, or refined safflower oil. Butter has a lower smoke point than most cooking oils, so if you prefer the flavor of butter, consider using clarified butter (ghee), which has a higher smoke point and is more suitable for high-temperature cooking. Additionally, using a cooking thermometer can help you monitor and maintain the correct frying temperature.