Cooking oil is any type of oil used to cook a variety of foods, typically meat. In earlier times, the use of oils that had been obtained from animal fats was found to be faster as compared to roasting and stewing. This became the start of the common method of frying food. Nowadays, with the discovery of cholesterol, which is present in animal fats, different healthier varieties of cooking oils have been developed. These cooking oil varieties include canola, olive and corn oil, which are generally called vegetable oils.
Vegetable Oils versus Animal Oils
It is common knowledge that oils obtained from animal fats contain a high amount of cholesterol when compared to vegetable oils. The smoke point of vegetable oils is also higher than that of animal fats. The smoke point of an oil refers to the temperature where it begins to give off visible fumes, a sign of its decomposition. When oil decomposes, it creates acreolein, an intolerable-smelling compound.
Re-using Frying Oil and Smoke Points
When oil is re-used for deep-frying, its smoke point decreases irreversibly. For instance, when cooking oil is used for deep-frying the first time and the temperature reaches a little over 190 degrees Celsius (typical temperature for deep-frying), its smoke point will decrease. Thus, the second time it is used for deep-frying it will immediately decompose even before the ideal temperature for deep-frying has been reached. Therefore, if it cannot be helped but to re-use oil for deep-frying, it would be better to use one that has the highest smoke point. Currently, safflower oil has the highest smoking point at 265 degrees Celsius while lard (animal fat) has the lowest smoking points at 183 to 205 degrees Celsius.
As for animal fats, there are a number of factors that can reduce its smoke point. Among these factors include the presence of foreign substances (like batter), the presence of salt, the number of times that it has been used and if it has been exposed to light, high temperature or oxygen.
It is important to be familiar with the signs of cooking oil that has deteriorated so you know when it is best to stop using it. Deteriorated oil is considerably darker because food and oil molecules burn due to prolonged or high heating. Repeatedly using the oil makes it thicker. Deteriorated oil will give off smoke even before it reaches the optimum deep-frying temperature. When this happens, oil can not effectively deep-fry food. If the cooking oil already smells like the food you have cooked in it or if it has a rancid smell, then your cooking oil has already deteriorated and eating food cooked in may be harmful to your health.