1. Fats and edible oil when allowed to stand for a longer time in iron or tin container becomes rancid.
2. The condition produced by oxidation of fats and oils in food marked by unpleasant smell and taste is called rancidity. When the oil is heated, it starts frothing and smells foul.
3. If the food is cooked in rancid oil, it gives an unpleasant smell and taste, making it unfit for consumption.
So, edible oil is not allowed to stand for a long time in an iron or tin container.