Fats and oils consist of triglycerides, three fatty acids attached to a glycerol backbone. The fatty acids attached to the backbone may be saturated; that is, there are only single bonds between all the carbon atoms on the chain, or unsaturated. Unsaturated fatty acids have one or more double bonds between the carbons.
The degree of unsaturation affects the physical characteristics of the oil and, hence, its functionality. The greater the degree of saturation, the harder the fat will be. The hydrogenation process allows oil processors to modify edible oils selectively. Hydrogenated oils can be fully saturated or partially saturated.