It would not stay pure once u opened it, provided the fact that it is properly sealed right after used.

You should keep in mind that ethanol is hygroscopic and reacts with water naturally breaking the bonds.

So best option is to store in dry and under less humidity and don't leave it uncapped.

Thank you very much for our reply Supongsenla Ao

Ethanol will indeed absorb water (although I doubt any "bonds will be broken"), but will not explain the smell. Many times another alcohol is added, e.g. methanol or isopropanol, to prevent people from drinking the ethanol, take a good look at the label on the bottle and see if this is the case

Thank you for your reply Yoram Gerchman . I went through the label on the bottle, and it appears 0.01% of methanol was on the contents.