Oxidizing means it breaks down due to being subject to the oxygen around it. Rust is oxidation of iron.
Originally Posted by kmodell
Some fats are very subject to oxidation (unsaturated and polyunsaturated in particular like the ones in almonds), and that is what makes them go rancid.
Flax seed when ground up oxidizes rather quickly, hence it should be stored in an air-tight container in the fridge once ground or if already ground, once opened.
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