Q. Why is it recommended that oil be stored in an airtight container?

Answer

For long-term oil storage an airtight container is preferable because: oil oxidizes in the presence of air. It's possible that this will cause the oil to get rancid and smell bad. Therefore to keep the oil from deteriorating due to air exposure it is best to store it in an airtight container. The odor and flavor of edible oil will alter if it is left out in the air for too long turning rancid. When edible oil is left out in the open for an extended period of time it oxidizes in the presence of oxygen and takes on a rancid flavor and aroma.