The fact is that vinegar which is usually made from fermented fruit juice also contains acetic acid which is the main reason for the smell of vinegar. As the aspirin breaks down into acetic acid and salicylic acid, the acetic acid in it causes the smell to be like that of vinegar. The aspirin starts to smell like vinegar in quick time when it breaks down into acetic acid. The common causes of the drug breaking down quickly are when it is stored in a place that is not cool and dry.