Linoleic acid and Alpha-linolenic acid are Essential Fatty Acids (EFAs) that are essential to our health. They are also very temperamental. Light, air, and heat destroy them. Nature packages these oils in seeds that keep out light, air, and heat. In nature’s package, these oils will sometimes keep for years without spoiling.
When we extract the oil from such seeds, we need to make sure that light, air, and heat are kept from the oil from before pressing until the oil is consumed. Special care needs to be taken in processing, packaging, and storing oils rich in EFAs. To set such conditions is expensive, and the necessary care is not usually taken.
Light, the greatest enemy of EFAs, produces free radicals in oils, and speeds up the reaction of oils with oxygen from the air by 1000 times, resulting in rancid oil. Light can induce cross-linking of fatty acid molecules into dimers and polymers that are rubber-like substances. Light-induced free radical chain reactions can break EFAs down into many different kinds of products, including aldehydes, ketones, and other toxic and non-toxic components. Light destroys the vital biological properties of the EFAs.
Oxygen, even in the absence of light, breaks down EFAs. The result is what we know as rancid oil, which has a scratchy, bitter, fishy, or painty taste, or a characteristic unpleasant smell, like a parking lot in August heat. Dozens of breakdown products form, with toxic or unknown effects on our body’s functions.
Heat, used in deodorizing, hydrogenation (to make margarines and shortenings), and commercial frying and deep-frying used to make consumer items, destroys EFAs by twisting their molecules from a natural cis- shape to an unnatural trans- shape. Frying and deep-frying in the home also twist the molecules.
Fresh EFA-rich oils should be pressed and packaged in the dark, in the absence of oxygen, and with minimal heat, then stored in opaque containers to prevent contact with light and oxygen. They should be shelf-dated. If they are frozen solid (which does not damage them), oils remain unspoiled for a long time. They should be shipped directly by manufacturer to retailer or consumer without stops along the way, to reach consumers quickly.
You can learn more about EFA’s in my book Fats That Heal Fats That Kill.