Storage of Fats and Rancidity

Although saturated fats resist rancidity better than unsaturated fats, it is best to protect both from this inevitable deterioration process. Fats such as butter and margarine are best stored in the refrigerator. Butter will keep for months in the freezer, but margarines do not freeze as well because their emulsions may separate. Shortenings and most oils should be kept tightly covered in a dark spot on the cupboard shelf; however, they will keep longer if refrigerated. Olive oil has a shorter shelf life than most vegetable oils and should be refrigerated fairly soon after opening.

Rancidity of Fats

Rancidity is the chemical deterioration of fats, which occurs when the triglyceride molecule and/or the fatty acids attached to the glycerol molecule are broken down into smaller units that yield off-flavors and odors. The longer a fat is stored, the greater the possibility of its becoming rancid. Fats and oils used in cooking can also become rancid as they are exposed to oxygen, heat, or light. For this reason, they should be checked frequently for rancidity, since using a rancid fat or oil to make cakes, cookies, or other baked goods will adversely affect their flavor. Rancid fat will also ruin the flavor of sauteed or fried foods and cause problems during heating because of its lower smoke point.