Working System of Vinegar: The chemical structure of ethanoic acid in vinegar neutralize the active site of microorganism. The Pka value of Ethanoic acid is 4.75. So it creates acid medium which is not favorable of microorganism. In fact, enzyme producing from microorganism are responsible for food rottening. The lone pair electron present in nitrogen of protein chain is act as an active side for catalysis. But the proton (H+) presence in ethanoic acid neutralize the active side and that is why food remain unattached by microorganism.