Basic properties of Fats and Oils
Fats and oils are lipids and are important in designing a well-balanced meal plan. The effect of heat on fats and oils is of great importance to culinary science and again can be explained if the properties and chemistry of fats are understood. Included are melting points, smoke points, deterioration, and use as a cooking medium. Most fats do not have sharply defined melting points but they soften over a range of 10 degree to 20 degree F. The reason is the presence of a number of different triglycerides in a given fat. As the temperature rises, different ones melt. The length and degree of unsaturation in the fatty acid components greatly determine the melting point. It is this response of fats to temperature that facilitates the spreading of melting butter on toast and basting with melting fats.
Fats and oils have much higher boiling than does water because of their large molecular size. Fats are nonpolar so they do not form hydrogen bonds. They do, however, form weaker bonds all along their large molecule. It takes relatively high temperature to break all of them and convert the liquid to a gas. The smoke point is defined as the point when visible gaseous products are produced from fat breakdown. This point seems to depend on the initial amount of free fatty aids in the oil or fat. The amount of free fatty acids is generally much lower in vegetable oil or than animal fats. Other material in fats, such as carbohydrates, proteins and emulsifiers, will lower the smoke points. As the fat or oil is used, the smoke pointy lowers due to breakdown of the fats and the build up of other materials. Caution must be taken when smoke appears because it is a warning that the ignition point is nearing.
Other factors that can deteriorate fats and oils are absorption of odors and rancidity. When using fats and oils as a cooking medium, smoke point, absorbed odors, and rancidity all must be observed closely or one risks a fire or the transmission of off flavors and odors to the foods. Foods are cooked in fats by sautéing and deep-fat frying. Liquid fats and oils are better heat conductors than air, and foods heated in fats are not only cooked but also browned due to caramelization and the sugar protein reaction. Texture is important as these fried foods must be crisp.
Basic properties of Fats and Oils
