Healthful oils are essential to our health, but they are more temperamental than the inferior oils you see on the supermarket shelves. Light, air, and heat can destroy them. Nature packages these oils in seeds, and left intact, these oils will sometimes keep for years without spoiling.
When we extract the oil from such seeds, we need to make sure the oil is shielded from the destructive elements before pressing and until the oil is opened. Special care needs to be taken in processing, packaging, and storing oils rich in essential fats to prevent the oil from turning rancid. Rancid oil has a scratchy, bitter, fishy, or paint-like taste, and may be accompanied by a characteristic unpleasant smell. When oil has turned rancid, dozens of by-products form, with toxic or unknown effects on our bodies’ functions. In fact, rancid oils, if consumed, have been associated with negative health effects such as arterial damage, inflammation, certain forms of cancer, and premature aging. It is, therefore, imperative that cooking oils are properly stored to minimize exposure to these negative factors.
Below are general guidelines to maximize shelf life and overall quality of your cooking fats and oils:
1) Choose fresh EFA-rich oils that have been pressed and packaged in the dark, in the absence of oxygen, and with minimal heat, and packaged in opaque bottles.
2) At home, once you have opened a bottle of good oil, it should be stored in the refrigerator to protect it from turning rancid. Refrigerated oils will generally turn cloudy when cold; however, simply remove the oil an hour or two prior to use and it will return to its original liquid state. If refrigeration is not possible, store all oils in a cool-cold, dry, dark place (not a warm pantry!).
3) Prior to opening, the oil is safe in a bottle on a shelf at room temperature; this is because during the packaging process, the oil was packaged in the absence of the destructive elements and then sealed tightly.
4) Be sure to keep your healthful oils away from the stove, and do not leave them on top of the fridge or microwave.
5) With regards to butter, store unused portions in the freezer as butter will maintain its quality only for approximately two weeks in the refrigerator.
6) Keep in mind that darker-colored oils will go rancid more quickly than lighter-colored oils. Unrefined oils will generally keep for three to six months once opened if properly stored in a cool, dark location.
7) Refined oils will keep twice as long as unrefined oils— generally six to twelve months once opened when stored in a cool, dark location.
8) Oils high in polyunsaturated fats have a shorter shelf life than oils high in monounsaturated or saturated fats.
9) Unopened cooking oils generally have a shelf life of one year if properly stored in a cool, dark, dry place.